28. Fragment Operations
Fragments produced by rasterization go through a number of operations to determine whether or how values produced by fragment shading are written to the framebuffer.
The following fragment operations adhere to rasterization order, and are typically performed in this order:
The coverage mask generated by
rasterization describes the initial coverage of each sample covered by the
fragment.
Fragment operations will update the coverage mask to add or subtract
coverage where appropriate.
If a fragment operation results in all bits of the coverage mask being 0,
the fragment is discarded, and no further operations are performed.
Fragments can also be programmatically discarded in a fragment shader by
executing one of
-
OpTerminateInvocation -
OpDemoteToHelperInvocationEXT -
OpKill.
When one of the fragment operations in this chapter is described as “replacing” a fragment shader output, that output is replaced unconditionally, even if no fragment shader previously wrote to that output.
If the fragment shader declares the
PostDepthCoverage execution mode, the sample mask
test is instead performed after the depth test.
If the fragment shader declares the
EarlyFragmentTests execution mode, fragment shading
and multisample coverage operations should instead be
performed after sample counting.
If the fragment shader declares the
EarlyAndLateFragmentTestsAMD execution mode, and does not declare the
StencilRefReplacingEXT or
DepthReplacing execution mode, fragment shading and
multisample coverage operations are instead be performed
after sample counting.
For a pipeline with the following properties:
-
the fragment shader either specifies
EarlyAndLateFragmentTestsAMDor does not write to storage resources; -
the fragment shader specifies the
StencilRefReplacingEXTexecution mode; -
either
-
the fragment shader specifies the
StencilRefUnchangedFrontAMDexecution mode; -
the fragment shader specifies the
StencilRefGreaterFrontAMDexecution mode and the pipeline uses a VkPipelineDepthStencilStateCreateInfo::front.compareOpofVK_COMPARE_OP_GREATERorVK_COMPARE_OP_GREATER_OR_EQUAL; or -
the fragment shader specifies the
StencilRefLessFrontAMDexecution mode and the pipeline uses a VkPipelineDepthStencilStateCreateInfo::front.compareOpofVK_COMPARE_OP_LESSorVK_COMPARE_OP_LESS_OR_EQUAL; and
-
-
either
-
the fragment shader specifies the
StencilRefUnchangedBackAMDexecution mode; -
the fragment shader specifies the
StencilRefGreaterBackAMDexecution mode and the pipeline uses a VkPipelineDepthStencilStateCreateInfo::back.compareOpofVK_COMPARE_OP_GREATERorVK_COMPARE_OP_GREATER_OR_EQUAL; or -
the fragment shader specifies the
StencilRefLessBackAMDexecution mode and the pipeline uses a VkPipelineDepthStencilStateCreateInfo::back.compareOpofVK_COMPARE_OP_LESSorVK_COMPARE_OP_LESS_OR_EQUAL
-
an additional stencil test may be performed before
fragment shading, using the stencil reference value
specified by
VkPipelineDepthStencilStateCreateInfo::front.reference or
VkPipelineDepthStencilStateCreateInfo::back.reference.
For a pipeline with the following properties:
-
the fragment shader either specifies
EarlyAndLateFragmentTestsAMDor does not write to storage resources; -
the fragment shader specifies the
DepthReplacingexecution mode; and -
either
-
the fragment shader specifies the
DepthUnchangedexecution mode; -
the fragment shader specifies the
DepthGreaterexecution mode and the pipeline uses a VkPipelineDepthStencilStateCreateInfo::depthCompareOpofVK_COMPARE_OP_GREATERorVK_COMPARE_OP_GREATER_OR_EQUAL; or -
the fragment shader specifies the
DepthLessexecution mode and the pipeline uses a VkPipelineDepthStencilStateCreateInfo::depthCompareOpofVK_COMPARE_OP_LESSorVK_COMPARE_OP_LESS_OR_EQUAL
-
the implementation may perform depth bounds test before fragment shading and perform an additional depth test immediately after that using the interpolated depth value generated by rasterization.
Once all fragment operations have completed, fragment shader outputs for covered color attachment samples pass through framebuffer operations.
28.1. Discard Rectangles Test
The discard rectangle test compares the framebuffer coordinates (xf,yf) of each sample covered by a fragment against a set of discard rectangles.
Each discard rectangle is defined by a VkRect2D. These values are either set by the VkPipelineDiscardRectangleStateCreateInfoEXT structure during pipeline creation, or dynamically by the vkCmdSetDiscardRectangleEXT command.
A given sample is considered inside a discard rectangle if the xf is
in the range [VkRect2D::offset.x, VkRect2D::offset.x +
VkRect2D::extent.x), and yf is in the range
[VkRect2D::offset.y, VkRect2D::offset.y +
VkRect2D::extent.y).
If the test is set to be inclusive, samples that are not inside any of the
discard rectangles will have their coverage set to 0.
If the test is set to be exclusive, samples that are inside any of the
discard rectangles will have their coverage set to 0.
If no discard rectangles are specified, the coverage mask is unmodified by this operation.
The VkPipelineDiscardRectangleStateCreateInfoEXT structure is defined
as:
// Provided by VK_EXT_discard_rectangles
typedef struct VkPipelineDiscardRectangleStateCreateInfoEXT {
VkStructureType sType;
const void* pNext;
VkPipelineDiscardRectangleStateCreateFlagsEXT flags;
VkDiscardRectangleModeEXT discardRectangleMode;
uint32_t discardRectangleCount;
const VkRect2D* pDiscardRectangles;
} VkPipelineDiscardRectangleStateCreateInfoEXT;-
sTypeis the type of this structure. -
pNextisNULLor a pointer to a structure extending this structure. -
flagsis reserved for future use. -
discardRectangleModeis a VkDiscardRectangleModeEXT value determining whether the discard rectangle test is inclusive or exclusive. -
discardRectangleCountis the number of discard rectangles to use. -
pDiscardRectanglesis a pointer to an array of VkRect2D structures defining discard rectangles.
If the VK_DYNAMIC_STATE_DISCARD_RECTANGLE_EXT dynamic state is enabled
for a pipeline, the pDiscardRectangles member is ignored.
When this structure is included in the pNext chain of
VkGraphicsPipelineCreateInfo, it defines parameters of the discard
rectangle test.
If this structure is not included in the pNext chain, it is equivalent
to specifying this structure with a discardRectangleCount of 0.
// Provided by VK_EXT_discard_rectangles
typedef VkFlags VkPipelineDiscardRectangleStateCreateFlagsEXT;VkPipelineDiscardRectangleStateCreateFlagsEXT is a bitmask type for
setting a mask, but is currently reserved for future use.
VkDiscardRectangleModeEXT values are:
// Provided by VK_EXT_discard_rectangles
typedef enum VkDiscardRectangleModeEXT {
VK_DISCARD_RECTANGLE_MODE_INCLUSIVE_EXT = 0,
VK_DISCARD_RECTANGLE_MODE_EXCLUSIVE_EXT = 1,
} VkDiscardRectangleModeEXT;-
VK_DISCARD_RECTANGLE_MODE_INCLUSIVE_EXTspecifies that the discard rectangle test is inclusive. -
VK_DISCARD_RECTANGLE_MODE_EXCLUSIVE_EXTspecifies that the discard rectangle test is exclusive.
To dynamically set the discard rectangles, call:
// Provided by VK_EXT_discard_rectangles
void vkCmdSetDiscardRectangleEXT(
VkCommandBuffer commandBuffer,
uint32_t firstDiscardRectangle,
uint32_t discardRectangleCount,
const VkRect2D* pDiscardRectangles);-
commandBufferis the command buffer into which the command will be recorded. -
firstDiscardRectangleis the index of the first discard rectangle whose state is updated by the command. -
discardRectangleCountis the number of discard rectangles whose state are updated by the command. -
pDiscardRectanglesis a pointer to an array of VkRect2D structures specifying discard rectangles.
The discard rectangle taken from element i of pDiscardRectangles
replace the current state for the discard rectangle at index
firstDiscardRectangle + i, for i in [0,
discardRectangleCount).
This command sets the discard rectangles for subsequent drawing commands
when the graphics pipeline is created with
VK_DYNAMIC_STATE_DISCARD_RECTANGLE_EXT set in
VkPipelineDynamicStateCreateInfo::pDynamicStates.
Otherwise, this state is specified by the
VkPipelineDiscardRectangleStateCreateInfoEXT::pDiscardRectangles
values used to create the currently active pipeline.
28.2. Scissor Test
The scissor test compares the framebuffer coordinates (xf,yf) of
each sample covered by a fragment against a scissor rectangle at the index
equal to the fragment’s ViewportIndex.
Each scissor rectangle is defined by a VkRect2D. These values are either set by the VkPipelineViewportStateCreateInfo structure during pipeline creation, or dynamically by the vkCmdSetScissor command.
A given sample is considered inside a scissor rectangle if xf is in
the range [VkRect2D::offset.x, VkRect2D::offset.x +
VkRect2D::extent.x), and yf is in the range
[VkRect2D::offset.y, VkRect2D::offset.y +
VkRect2D::extent.y).
Samples with coordinates outside the scissor rectangle at the corresponding
ViewportIndex will have their coverage set to 0.
If a render pass transform is enabled, the (offset.x and
offset.y) and (extent.width and extent.height) values are
transformed as described in render
pass transform before participating in the scissor test.
To dynamically set the scissor rectangles, call:
// Provided by VK_VERSION_1_0
void vkCmdSetScissor(
VkCommandBuffer commandBuffer,
uint32_t firstScissor,
uint32_t scissorCount,
const VkRect2D* pScissors);-
commandBufferis the command buffer into which the command will be recorded. -
firstScissoris the index of the first scissor whose state is updated by the command. -
scissorCountis the number of scissors whose rectangles are updated by the command. -
pScissorsis a pointer to an array of VkRect2D structures defining scissor rectangles.
The scissor rectangles taken from element i of pScissors replace
the current state for the scissor index firstScissor + i,
for i in [0, scissorCount).
This command sets the scissor rectangles for subsequent drawing commands
when the graphics pipeline is created with VK_DYNAMIC_STATE_SCISSOR
set in VkPipelineDynamicStateCreateInfo::pDynamicStates.
Otherwise, this state is specified by the
VkPipelineViewportStateCreateInfo::pScissors values used to
create the currently active pipeline.
28.3. Exclusive Scissor Test
The exclusive scissor test compares the framebuffer coordinates
(xf,yf) of each sample covered by a fragment against an exclusive
scissor rectangle at the index equal to the fragment’s
ViewportIndex.
Each exclusive scissor rectangle is defined by a VkRect2D. These values are either set by the VkPipelineViewportExclusiveScissorStateCreateInfoNV structure during pipeline creation, or dynamically by the vkCmdSetExclusiveScissorNV command.
A given sample is considered inside an exclusive scissor rectangle if
xf is in the range [VkRect2D::offset.x,
VkRect2D::offset.x + VkRect2D::extent.x), and yf
is in the range [VkRect2D::offset.y, VkRect2D::offset.y
+ VkRect2D::extent.y).
Samples with coordinates inside the exclusive scissor rectangle at the
corresponding ViewportIndex will have their coverage set to 0.
If no exclusive scissor rectangles are specified, the coverage mask is unmodified by this operation.
The VkPipelineViewportExclusiveScissorStateCreateInfoNV structure is
defined as:
// Provided by VK_NV_scissor_exclusive
typedef struct VkPipelineViewportExclusiveScissorStateCreateInfoNV {
VkStructureType sType;
const void* pNext;
uint32_t exclusiveScissorCount;
const VkRect2D* pExclusiveScissors;
} VkPipelineViewportExclusiveScissorStateCreateInfoNV;-
sTypeis the type of this structure. -
pNextisNULLor a pointer to a structure extending this structure. -
exclusiveScissorCountis the number of exclusive scissor rectangles. -
pExclusiveScissorsis a pointer to an array of VkRect2D structures defining exclusive scissor rectangles.
If the VK_DYNAMIC_STATE_EXCLUSIVE_SCISSOR_NV dynamic state is enabled
for a pipeline, the pExclusiveScissors member is ignored.
When this structure is included in the pNext chain of
VkGraphicsPipelineCreateInfo, it defines parameters of the exclusive
scissor test.
If this structure is not included in the pNext chain, it is equivalent
to specifying this structure with a exclusiveScissorCount of 0.
To dynamically set the exclusive scissor rectangles, call:
// Provided by VK_NV_scissor_exclusive
void vkCmdSetExclusiveScissorNV(
VkCommandBuffer commandBuffer,
uint32_t firstExclusiveScissor,
uint32_t exclusiveScissorCount,
const VkRect2D* pExclusiveScissors);-
commandBufferis the command buffer into which the command will be recorded. -
firstExclusiveScissoris the index of the first exclusive scissor rectangle whose state is updated by the command. -
exclusiveScissorCountis the number of exclusive scissor rectangles updated by the command. -
pExclusiveScissorsis a pointer to an array of VkRect2D structures defining exclusive scissor rectangles.
The scissor rectangles taken from element i of
pExclusiveScissors replace the current state for the scissor index
firstExclusiveScissor + i, for i in [0,
exclusiveScissorCount).
This command sets the exclusive scissor rectangles for subsequent drawing
commands when the graphics pipeline is created with
VK_DYNAMIC_STATE_EXCLUSIVE_SCISSOR_NV set in
VkPipelineDynamicStateCreateInfo::pDynamicStates.
Otherwise, this state is specified by the
VkPipelineViewportExclusiveScissorStateCreateInfoNV::pExclusiveScissors
values used to create the currently active pipeline.
28.4. Sample Mask Test
The sample mask test compares the coverage mask for a fragment with the sample mask defined by
VkPipelineMultisampleStateCreateInfo::pSampleMask.
Each bit of the coverage mask is associated with a sample index as described
in the rasterization chapter.
If the bit in VkPipelineMultisampleStateCreateInfo::pSampleMask
which is associated with that same sample index is set to 0, the coverage
mask bit is set to 0.
28.5. Fragment Shading
Fragment shaders are invoked for each fragment, or as helper invocations.
Most operations in the fragment shader are not performed in rasterization order, with exceptions called out in the following sections.
For fragment shaders invoked by fragments, the following rules apply:
-
A fragment shader must not be executed if a fragment operation that executes before fragment shading discards the fragment.
-
A fragment shader may not be executed if:
-
An implementation determines that another fragment shader, invoked by a subsequent primitive in primitive order, overwrites all results computed by the shader (including writes to storage resources).
-
Any other fragment operation discards the fragment, and the shader does not write to any storage resources.
-
-
Otherwise, at least one fragment shader must be executed.
-
If sample shading is enabled and multiple invocations per fragment are required, additional invocations must be executed as specified.
-
If a shading rate image is used and multiple invocations per fragment are required, additional invocations must be executed as specified.
-
Each covered sample must be included in at least one fragment shader invocation.
-
|
Note
Multiple fragment shader invocations may be executed for the same fragment for any number of implementation-dependent reasons. When there is more than one fragment shader invocation per fragment, the association of samples to invocations is implementation-dependent. Stores and atomics performed by these additional invocations have the normal effect. For example, if the subpass includes multiple views in its view mask, a fragment shader may be invoked separately for each view. Similarly, if the render pass has a fragment density map attachment, more
than one fragment shader invocation may be invoked for each covered sample.
Such additional invocations are only produced if
|
28.5.1. Sample Mask
Reading from the SampleMask built-in in the Input storage class will return the
coverage mask for the current fragment as calculated by fragment operations
that executed prior to fragment shading.
If sample shading is enabled, fragment shaders
will only see values of 1 for samples being shaded - other bits will be
0.
Each bit of the coverage mask is associated with a sample index as described
in the rasterization chapter.
If the bit in SampleMask which is associated with that same sample
index is set to 0, that coverage mask bit is set to 0.
Values written to the SampleMask built-in in the Output storage class will be used by
the multisample coverage operation, with the same encoding
as the input built-in.
28.5.2. Depth Replacement
Writing to the FragDepth
built-in will replace the fragment’s calculated depth values for each sample
in the input SampleMask.
Depth testing performed after the fragment shader for
this fragment will use this new value as zf.
28.5.3. Stencil Reference Replacement
Writing to the
FragStencilRefEXT built-in
will replace the fragment’s stencil reference value for each sample in the
input SampleMask.
Stencil testing performed after the fragment shader for
this fragment will use this new value as sr.
28.5.4. Interlocked Operations
OpBeginInvocationInterlockEXT and OpEndInvocationInterlockEXT
define a section of a fragment shader which imposes additional ordering
constraints on operations performed within them.
These operations are defined as interlocked operations.
How interlocked operations are ordered against other fragment shader
invocations depends on the specified execution modes.
If the ShadingRateInterlockOrderedEXT execution mode is specified, any
interlocked operations in a fragment shader must happen before interlocked
operations in fragment shader invocations that execute later in
rasterization order and cover at least one sample in
the same fragment area, and must happen after interlocked operations in a
fragment shader that executes earlier in rasterization
order and cover at least one sample in the same fragment area.
If the ShadingRateInterlockUnorderedEXT execution mode is specified,
any interlocked operations in a fragment shader must happen before or after
interlocked operations in fragment shader invocations that execute earlier
or later in rasterization order and cover at least one
sample in the same fragment area.
If the PixelInterlockOrderedEXT execution mode is specified, any
interlocked operations in a fragment shader must happen before interlocked
operations in fragment shader invocations that execute later in
rasterization order and cover at least one sample in
the same pixel, and must happen after interlocked operations in a fragment
shader that executes earlier in rasterization order and
cover at least one sample in the same pixel.
If the PixelInterlockUnorderedEXT execution mode is specified, any
interlocked operations in a fragment shader must happen before or after
interlocked operations in fragment shader invocations that execute earlier
or later in rasterization order and cover at least one
sample in the same pixel.
If the SampleInterlockOrderedEXT execution mode is specified, any
interlocked operations in a fragment shader must happen before interlocked
operations in fragment shader invocations that execute later in
rasterization order and cover at least one of the same
samples, and must happen after interlocked operations in a fragment shader
that executes earlier in rasterization order and cover
at least one of the same samples.
If the SampleInterlockUnorderedEXT execution mode is specified, any
interlocked operations in a fragment shader must happen before or after
interlocked operations in fragment shader invocations that execute earlier
or later in rasterization order and cover at least one
of the same samples.
28.6. Multisample Coverage
If a fragment shader is active and its entry point’s interface includes a
built-in output variable decorated with SampleMask,
but not OverrideCoverageNV,
the coverage mask is ANDed with the bits of the SampleMask
built-in to generate a new coverage mask.
If the SampleMask built-in is also decorated with
OverrideCoverageNV, the coverage mask is replaced with the mask bits
set in the shader.
If sample shading is enabled, bits written to
SampleMask corresponding to samples that are not being shaded by the
fragment shader invocation are ignored.
If no fragment shader is active, or if the active fragment shader does not
include SampleMask in its interface, the coverage mask is not modified.
Next, the fragment alpha value and coverage mask are modified based on the
line coverage factor if the lineRasterizationMode member of the
VkPipelineRasterizationStateCreateInfo structure is
VK_LINE_RASTERIZATION_MODE_RECTANGULAR_SMOOTH_EXT, and the
alphaToCoverageEnable and alphaToOneEnable members of the
VkPipelineMultisampleStateCreateInfo structure.
All alpha values in this section refer only to the alpha component of the
fragment shader output that has a Location and Index decoration of
zero (see the Fragment Output Interface
section).
If that shader output has an integer or unsigned integer type, then these
operations are skipped.
If the lineRasterizationMode member of the
VkPipelineRasterizationStateCreateInfo structure is
VK_LINE_RASTERIZATION_MODE_RECTANGULAR_SMOOTH_EXT and the fragment
came from a line segment, then the alpha value is replaced by multiplying it
by the coverage factor for the fragment computed during
smooth line rasterization.
If alphaToCoverageEnable is enabled, a temporary coverage mask is
generated where each bit is determined by the fragment’s alpha value, which
is ANDed with the fragment coverage mask.
No specific algorithm is specified for converting the alpha value to a temporary coverage mask. It is intended that the number of 1’s in this value be proportional to the alpha value (clamped to [0,1]), with all 1’s corresponding to a value of 1.0 and all 0’s corresponding to 0.0. The algorithm may be different at different framebuffer coordinates.
|
Note
Using different algorithms at different framebuffer coordinates may help to avoid artifacts caused by regular coverage sample locations. |
Finally, if alphaToOneEnable is enabled, each alpha value is replaced
by the maximum representable alpha value for fixed-point color attachments,
or by 1.0 for floating-point attachments.
Otherwise, the alpha values are not changed.
28.7. Depth and Stencil Operations
Pipeline state controlling the depth bounds tests,
stencil test, and depth test is
specified through the members of the
VkPipelineDepthStencilStateCreateInfo structure.
The VkPipelineDepthStencilStateCreateInfo structure is defined as:
// Provided by VK_VERSION_1_0
typedef struct VkPipelineDepthStencilStateCreateInfo {
VkStructureType sType;
const void* pNext;
VkPipelineDepthStencilStateCreateFlags flags;
VkBool32 depthTestEnable;
VkBool32 depthWriteEnable;
VkCompareOp depthCompareOp;
VkBool32 depthBoundsTestEnable;
VkBool32 stencilTestEnable;
VkStencilOpState front;
VkStencilOpState back;
float minDepthBounds;
float maxDepthBounds;
} VkPipelineDepthStencilStateCreateInfo;-
sTypeis the type of this structure. -
pNextisNULLor a pointer to a structure extending this structure. -
flagsis a bitmask of VkPipelineDepthStencilStateCreateFlagBits specifying additional depth/stencil state information. -
depthTestEnablecontrols whether depth testing is enabled. -
depthWriteEnablecontrols whether depth writes are enabled whendepthTestEnableisVK_TRUE. Depth writes are always disabled whendepthTestEnableisVK_FALSE. -
depthCompareOpis a VkCompareOp value specifying the comparison operator to use in the Depth Comparison step of the depth test. -
depthBoundsTestEnablecontrols whether depth bounds testing is enabled. -
stencilTestEnablecontrols whether stencil testing is enabled. -
frontandbackcontrol the parameters of the stencil test. -
minDepthBoundsis the minimum depth bound used in the depth bounds test. -
maxDepthBoundsis the maximum depth bound used in the depth bounds test.
VkPipelineDepthStencilStateCreateFlags is a bitmask type for setting a
mask of zero or more VkPipelineDepthStencilStateCreateFlagBits.
Bits which can be set in the
VkPipelineDepthStencilStateCreateInfo::flags parameter are:
// Provided by VK_ARM_rasterization_order_attachment_access
typedef enum VkPipelineDepthStencilStateCreateFlagBits {
// Provided by VK_ARM_rasterization_order_attachment_access
VK_PIPELINE_DEPTH_STENCIL_STATE_CREATE_RASTERIZATION_ORDER_ATTACHMENT_DEPTH_ACCESS_BIT_ARM = 0x00000001,
// Provided by VK_ARM_rasterization_order_attachment_access
VK_PIPELINE_DEPTH_STENCIL_STATE_CREATE_RASTERIZATION_ORDER_ATTACHMENT_STENCIL_ACCESS_BIT_ARM = 0x00000002,
} VkPipelineDepthStencilStateCreateFlagBits;-
VK_PIPELINE_DEPTH_STENCIL_STATE_CREATE_RASTERIZATION_ORDER_ATTACHMENT_DEPTH_ACCESS_BIT_ARMindicates that access to the depth aspects of depth/stencil and input attachments will have implicit framebuffer-local memory dependencies. See renderpass feedback loops for more information. -
VK_PIPELINE_DEPTH_STENCIL_STATE_CREATE_RASTERIZATION_ORDER_ATTACHMENT_STENCIL_ACCESS_BIT_ARMindicates that access to the stencil aspects of depth/stencil and input attachments will have implicit framebuffer-local memory dependencies. See renderpass feedback loops for more information.
28.8. Depth Bounds Test
The depth bounds test compares the depth value za in the depth/stencil attachment at each sample’s framebuffer coordinates (xf,yf) and sample index i against a set of depth bounds.
The depth bounds are determined by two floating point values defining a
minimum (minDepthBounds) and maximum (maxDepthBounds) depth
value.
These values are either set by the
VkPipelineDepthStencilStateCreateInfo structure during pipeline
creation, or dynamically by
vkCmdSetDepthBoundsTestEnable and
vkCmdSetDepthBounds.
A given sample is considered within the depth bounds if za is in the
range [minDepthBounds,maxDepthBounds].
Samples with depth attachment values outside of the depth bounds will have
their coverage set to 0.
If the depth bounds test is disabled, or if there is no depth attachment, the coverage mask is unmodified by this operation.
To dynamically enable or disable the depth bounds test, call:
// Provided by VK_VERSION_1_3
void vkCmdSetDepthBoundsTestEnable(
VkCommandBuffer commandBuffer,
VkBool32 depthBoundsTestEnable);or the equivalent command
// Provided by VK_EXT_extended_dynamic_state
void vkCmdSetDepthBoundsTestEnableEXT(
VkCommandBuffer commandBuffer,
VkBool32 depthBoundsTestEnable);-
commandBufferis the command buffer into which the command will be recorded. -
depthBoundsTestEnablespecifies if the depth bounds test is enabled.
This command sets the depth bounds enable for subsequent drawing commands
when the graphics pipeline is created with
VK_DYNAMIC_STATE_DEPTH_BOUNDS_TEST_ENABLE set in
VkPipelineDynamicStateCreateInfo::pDynamicStates.
Otherwise, this state is specified by the
VkPipelineDepthStencilStateCreateInfo::depthBoundsTestEnable
value used to create the currently active pipeline.
To dynamically set the depth bounds range, call:
// Provided by VK_VERSION_1_0
void vkCmdSetDepthBounds(
VkCommandBuffer commandBuffer,
float minDepthBounds,
float maxDepthBounds);-
commandBufferis the command buffer into which the command will be recorded. -
minDepthBoundsis the minimum depth bound. -
maxDepthBoundsis the maximum depth bound.
This command sets the depth bounds range for subsequent drawing commands
when the graphics pipeline is created with
VK_DYNAMIC_STATE_DEPTH_BOUNDS set in
VkPipelineDynamicStateCreateInfo::pDynamicStates.
Otherwise, this state is specified by the
VkPipelineDepthStencilStateCreateInfo::minDepthBounds and
VkPipelineDepthStencilStateCreateInfo::maxDepthBounds values
used to create the currently active pipeline.
28.9. Stencil Test
The stencil test compares the stencil attachment value sa in the depth/stencil attachment at each sample’s framebuffer coordinates (xf,yf) and sample index i against a stencil reference value.
If the render pass has a fragment density map attachment and the fragment covers multiple pixels, there is an implementation-dependent association of coverage samples to stencil attachment samples within the fragment. However, if all samples in the fragment are covered, and the stencil attachment value is updated as a result of this test, all stencil attachment samples will be updated.
If the stencil test is not enabled, as specified by
vkCmdSetStencilTestEnable or
VkPipelineDepthStencilStateCreateInfo::stencilTestEnable, or if
there is no stencil attachment, the coverage mask is unmodified by this
operation.
The stencil test is controlled by one of two sets of stencil-related state, the front stencil state and the back stencil state. Stencil tests and writes use the back stencil state when processing fragments generated by back-facing polygons, and the front stencil state when processing fragments generated by front-facing polygons or any other primitives.
The comparison operation performed is determined by the VkCompareOp
value set by
vkCmdSetStencilOp::compareOp, or by
VkStencilOpState::compareOp during pipeline creation.
The compare mask sc and stencil reference value sr of the front or the back stencil state set determine arguments of the comparison operation. sc is set by the VkPipelineDepthStencilStateCreateInfo structure during pipeline creation, or by the vkCmdSetStencilCompareMask command. sr is set by VkPipelineDepthStencilStateCreateInfo or by vkCmdSetStencilReference.
sr and sa are each independently combined with sc
using a bitwise AND operation to create masked reference and attachment
values s'r and s'a.
s'r and s'a are used as the reference and test values,
respectively, in the operation specified by the VkCompareOp.
If the comparison evaluates to false, the coverage for the sample is set to
0.
A new stencil value sg is generated according to a stencil operation
defined by VkStencilOp parameters set by
vkCmdSetStencilOp or
VkPipelineDepthStencilStateCreateInfo.
If the stencil test fails, failOp defines the stencil operation used.
If the stencil test passes however, the stencil op used is based on the
depth test - if it passes,
VkPipelineDepthStencilStateCreateInfo::passOp is used, otherwise
VkPipelineDepthStencilStateCreateInfo::depthFailOp is used.
The stencil attachment value sa is then updated with the generated
stencil value sg according to the write mask sw defined by
VkPipelineDepthStencilStateCreateInfo::writeMask as:
-
sa = (sa & ¬sw) | (sg & sw)
To dynamically enable or disable the stencil test, call:
// Provided by VK_VERSION_1_3
void vkCmdSetStencilTestEnable(
VkCommandBuffer commandBuffer,
VkBool32 stencilTestEnable);or the equivalent command
// Provided by VK_EXT_extended_dynamic_state
void vkCmdSetStencilTestEnableEXT(
VkCommandBuffer commandBuffer,
VkBool32 stencilTestEnable);-
commandBufferis the command buffer into which the command will be recorded. -
stencilTestEnablespecifies if the stencil test is enabled.
This command sets the stencil test enable for subsequent drawing commands
when the graphics pipeline is created with
VK_DYNAMIC_STATE_STENCIL_TEST_ENABLE set in
VkPipelineDynamicStateCreateInfo::pDynamicStates.
Otherwise, this state is specified by the
VkPipelineDepthStencilStateCreateInfo::stencilTestEnable value
used to create the currently active pipeline.
To dynamically set the stencil operation, call:
// Provided by VK_VERSION_1_3
void vkCmdSetStencilOp(
VkCommandBuffer commandBuffer,
VkStencilFaceFlags faceMask,
VkStencilOp failOp,
VkStencilOp passOp,
VkStencilOp depthFailOp,
VkCompareOp compareOp);or the equivalent command
// Provided by VK_EXT_extended_dynamic_state
void vkCmdSetStencilOpEXT(
VkCommandBuffer commandBuffer,
VkStencilFaceFlags faceMask,
VkStencilOp failOp,
VkStencilOp passOp,
VkStencilOp depthFailOp,
VkCompareOp compareOp);-
commandBufferis the command buffer into which the command will be recorded. -
faceMaskis a bitmask of VkStencilFaceFlagBits specifying the set of stencil state for which to update the stencil operation. -
failOpis a VkStencilOp value specifying the action performed on samples that fail the stencil test. -
passOpis a VkStencilOp value specifying the action performed on samples that pass both the depth and stencil tests. -
depthFailOpis a VkStencilOp value specifying the action performed on samples that pass the stencil test and fail the depth test. -
compareOpis a VkCompareOp value specifying the comparison operator used in the stencil test.
This command sets the stencil operation for subsequent drawing commands when
the graphics pipeline is created with VK_DYNAMIC_STATE_STENCIL_OP set
in VkPipelineDynamicStateCreateInfo::pDynamicStates.
Otherwise, this state is specified by the corresponding
VkPipelineDepthStencilStateCreateInfo::failOp, passOp,
depthFailOp, and compareOp values used to create the currently
active pipeline, for both front and back faces.
The VkStencilOpState structure is defined as:
// Provided by VK_VERSION_1_0
typedef struct VkStencilOpState {
VkStencilOp failOp;
VkStencilOp passOp;
VkStencilOp depthFailOp;
VkCompareOp compareOp;
uint32_t compareMask;
uint32_t writeMask;
uint32_t reference;
} VkStencilOpState;-
failOpis a VkStencilOp value specifying the action performed on samples that fail the stencil test. -
passOpis a VkStencilOp value specifying the action performed on samples that pass both the depth and stencil tests. -
depthFailOpis a VkStencilOp value specifying the action performed on samples that pass the stencil test and fail the depth test. -
compareOpis a VkCompareOp value specifying the comparison operator used in the stencil test. -
compareMaskselects the bits of the unsigned integer stencil values participating in the stencil test. -
writeMaskselects the bits of the unsigned integer stencil values updated by the stencil test in the stencil framebuffer attachment. -
referenceis an integer stencil reference value that is used in the unsigned stencil comparison.
To dynamically set the stencil compare mask, call:
// Provided by VK_VERSION_1_0
void vkCmdSetStencilCompareMask(
VkCommandBuffer commandBuffer,
VkStencilFaceFlags faceMask,
uint32_t compareMask);-
commandBufferis the command buffer into which the command will be recorded. -
faceMaskis a bitmask of VkStencilFaceFlagBits specifying the set of stencil state for which to update the compare mask. -
compareMaskis the new value to use as the stencil compare mask.
This command sets the stencil compare mask for subsequent drawing commands
when the graphics pipeline is created with
VK_DYNAMIC_STATE_STENCIL_COMPARE_MASK set in
VkPipelineDynamicStateCreateInfo::pDynamicStates.
Otherwise, this state is specified by the
VkStencilOpState::compareMask value used to create the currently
active pipeline, for both front and back faces.
VkStencilFaceFlagBits values are:
// Provided by VK_VERSION_1_0
typedef enum VkStencilFaceFlagBits {
VK_STENCIL_FACE_FRONT_BIT = 0x00000001,
VK_STENCIL_FACE_BACK_BIT = 0x00000002,
VK_STENCIL_FACE_FRONT_AND_BACK = 0x00000003,
VK_STENCIL_FRONT_AND_BACK = VK_STENCIL_FACE_FRONT_AND_BACK,
} VkStencilFaceFlagBits;-
VK_STENCIL_FACE_FRONT_BITspecifies that only the front set of stencil state is updated. -
VK_STENCIL_FACE_BACK_BITspecifies that only the back set of stencil state is updated. -
VK_STENCIL_FACE_FRONT_AND_BACKis the combination ofVK_STENCIL_FACE_FRONT_BITandVK_STENCIL_FACE_BACK_BIT, and specifies that both sets of stencil state are updated.
// Provided by VK_VERSION_1_0
typedef VkFlags VkStencilFaceFlags;VkStencilFaceFlags is a bitmask type for setting a mask of zero or
more VkStencilFaceFlagBits.
To dynamically set the stencil write mask, call:
// Provided by VK_VERSION_1_0
void vkCmdSetStencilWriteMask(
VkCommandBuffer commandBuffer,
VkStencilFaceFlags faceMask,
uint32_t writeMask);-
commandBufferis the command buffer into which the command will be recorded. -
faceMaskis a bitmask of VkStencilFaceFlagBits specifying the set of stencil state for which to update the write mask, as described above for vkCmdSetStencilCompareMask. -
writeMaskis the new value to use as the stencil write mask.
This command sets the stencil write mask for subsequent drawing commands
when the graphics pipeline is created with
VK_DYNAMIC_STATE_STENCIL_WRITE_MASK set in
VkPipelineDynamicStateCreateInfo::pDynamicStates.
Otherwise, this state is specified by the
VkPipelineDepthStencilStateCreateInfo::writeMask value used to
create the currently active pipeline, for both front and back faces.
To dynamically set the stencil reference value, call:
// Provided by VK_VERSION_1_0
void vkCmdSetStencilReference(
VkCommandBuffer commandBuffer,
VkStencilFaceFlags faceMask,
uint32_t reference);-
commandBufferis the command buffer into which the command will be recorded. -
faceMaskis a bitmask of VkStencilFaceFlagBits specifying the set of stencil state for which to update the reference value, as described above for vkCmdSetStencilCompareMask. -
referenceis the new value to use as the stencil reference value.
This command sets the stencil reference value for subsequent drawing
commands when the graphics pipeline is created with
VK_DYNAMIC_STATE_STENCIL_REFERENCE set in
VkPipelineDynamicStateCreateInfo::pDynamicStates.
Otherwise, this state is specified by the
VkPipelineDepthStencilStateCreateInfo::reference value used to
create the currently active pipeline, for both front and back faces.
Possible values of the failOp, passOp, and depthFailOp
members of VkStencilOpState, specifying what happens to the stored
stencil value if this or certain subsequent tests fail or pass, are:
// Provided by VK_VERSION_1_0
typedef enum VkStencilOp {
VK_STENCIL_OP_KEEP = 0,
VK_STENCIL_OP_ZERO = 1,
VK_STENCIL_OP_REPLACE = 2,
VK_STENCIL_OP_INCREMENT_AND_CLAMP = 3,
VK_STENCIL_OP_DECREMENT_AND_CLAMP = 4,
VK_STENCIL_OP_INVERT = 5,
VK_STENCIL_OP_INCREMENT_AND_WRAP = 6,
VK_STENCIL_OP_DECREMENT_AND_WRAP = 7,
} VkStencilOp;-
VK_STENCIL_OP_KEEPkeeps the current value. -
VK_STENCIL_OP_ZEROsets the value to 0. -
VK_STENCIL_OP_REPLACEsets the value toreference. -
VK_STENCIL_OP_INCREMENT_AND_CLAMPincrements the current value and clamps to the maximum representable unsigned value. -
VK_STENCIL_OP_DECREMENT_AND_CLAMPdecrements the current value and clamps to 0. -
VK_STENCIL_OP_INVERTbitwise-inverts the current value. -
VK_STENCIL_OP_INCREMENT_AND_WRAPincrements the current value and wraps to 0 when the maximum value would have been exceeded. -
VK_STENCIL_OP_DECREMENT_AND_WRAPdecrements the current value and wraps to the maximum possible value when the value would go below 0.
For purposes of increment and decrement, the stencil bits are considered as an unsigned integer.
28.10. Depth Test
The depth test compares the depth value za in the depth/stencil attachment at each sample’s framebuffer coordinates (xf,yf) and sample index i against the sample’s depth value zf. If there is no depth attachment then the depth test is skipped.
If the render pass has a fragment density map attachment and the fragment covers multiple pixels, there is an implementation-dependent association of rasterization samples to depth attachment samples within the fragment. However, if all samples in the fragment are covered, and the depth attachment value is updated as a result of this test, all depth attachment samples will be updated.
The depth test occurs in three stages, as detailed in the following sections.
28.10.1. Depth Clamping and Range Adjustment
If VkPipelineRasterizationStateCreateInfo::depthClampEnable is
enabled, before the sample’s zf is compared to za,
zf is clamped to [min(n,f),max(n,f)], where n and
f are the minDepth and maxDepth depth range values of the
viewport used by this fragment, respectively.
If depth clamping is not enabled and zf is not in the range [0, 1] and either VK_EXT_depth_range_unrestricted is not enabled, or the depth attachment has a fixed-point format, then zf is undefined following this step.
28.10.2. Depth Comparison
If the depth test is not enabled, as specified by
vkCmdSetDepthTestEnable or
VkPipelineDepthStencilStateCreateInfo::depthTestEnable, then
this step is skipped.
The comparison operation performed is determined by the VkCompareOp
value set by
vkCmdSetDepthCompareOp, or by
VkPipelineDepthStencilStateCreateInfo::depthCompareOp during
pipeline creation.
zf and za are used as the reference and test values,
respectively, in the operation specified by the VkCompareOp.
If the comparison evaluates to false, the coverage for the sample is set to
0.
28.10.3. Depth Attachment Writes
If depth writes are enabled, as specified by
vkCmdSetDepthWriteEnable or
VkPipelineDepthStencilStateCreateInfo::depthWriteEnable, and the
comparison evaluated to true, the depth attachment value za is set
to the sample’s depth value zf.
If there is no depth attachment, no value is written.
To dynamically enable or disable the depth test, call:
// Provided by VK_VERSION_1_3
void vkCmdSetDepthTestEnable(
VkCommandBuffer commandBuffer,
VkBool32 depthTestEnable);or the equivalent command
// Provided by VK_EXT_extended_dynamic_state
void vkCmdSetDepthTestEnableEXT(
VkCommandBuffer commandBuffer,
VkBool32 depthTestEnable);-
commandBufferis the command buffer into which the command will be recorded. -
depthTestEnablespecifies if the depth test is enabled.
This command sets the depth test enable for subsequent drawing commands when
the graphics pipeline is created with
VK_DYNAMIC_STATE_DEPTH_TEST_ENABLE set in
VkPipelineDynamicStateCreateInfo::pDynamicStates.
Otherwise, this state is specified by the
VkPipelineDepthStencilStateCreateInfo::depthTestEnable value
used to create the currently active pipeline.
To dynamically set the depth compare operator, call:
// Provided by VK_VERSION_1_3
void vkCmdSetDepthCompareOp(
VkCommandBuffer commandBuffer,
VkCompareOp depthCompareOp);or the equivalent command
// Provided by VK_EXT_extended_dynamic_state
void vkCmdSetDepthCompareOpEXT(
VkCommandBuffer commandBuffer,
VkCompareOp depthCompareOp);-
commandBufferis the command buffer into which the command will be recorded. -
depthCompareOpis a VkCompareOp value specifying the comparison operator used for the Depth Comparison step of the depth test.
This command sets the depth comparison operator for subsequent drawing
commands when the graphics pipeline is created with
VK_DYNAMIC_STATE_DEPTH_COMPARE_OP set in
VkPipelineDynamicStateCreateInfo::pDynamicStates.
Otherwise, this state is specified by the
VkPipelineDepthStencilStateCreateInfo::depthCompareOp value used
to create the currently active pipeline.
To dynamically set the depth write enable, call:
// Provided by VK_VERSION_1_3
void vkCmdSetDepthWriteEnable(
VkCommandBuffer commandBuffer,
VkBool32 depthWriteEnable);or the equivalent command
// Provided by VK_EXT_extended_dynamic_state
void vkCmdSetDepthWriteEnableEXT(
VkCommandBuffer commandBuffer,
VkBool32 depthWriteEnable);-
commandBufferis the command buffer into which the command will be recorded. -
depthWriteEnablespecifies if depth writes are enabled.
This command sets the depth write enable for subsequent drawing commands
when the graphics pipeline is created with
VK_DYNAMIC_STATE_DEPTH_WRITE_ENABLE set in
VkPipelineDynamicStateCreateInfo::pDynamicStates.
Otherwise, this state is specified by the
VkPipelineDepthStencilStateCreateInfo::depthWriteEnable value
used to create the currently active pipeline.
28.11. Representative Fragment Test
The representative fragment test allows implementations to reduce the amount of rasterization and fragment processing work performed for each point, line, or triangle primitive. For any primitive that produces one or more fragments that pass all prior early fragment tests, the implementation may choose one or more “representative” fragments for processing and discard all other fragments. For draw calls rendering multiple points, lines, or triangles arranged in lists, strips, or fans, the representative fragment test is performed independently for each of those primitives. The set of fragments discarded by the representative fragment test is implementation-dependent. In some cases, the representative fragment test may not discard any fragments for a given primitive.
If the pNext chain of VkGraphicsPipelineCreateInfo includes a
VkPipelineRepresentativeFragmentTestStateCreateInfoNV structure, then
that structure includes parameters controlling the representative fragment
test.
The VkPipelineRepresentativeFragmentTestStateCreateInfoNV structure is
defined as:
// Provided by VK_NV_representative_fragment_test
typedef struct VkPipelineRepresentativeFragmentTestStateCreateInfoNV {
VkStructureType sType;
const void* pNext;
VkBool32 representativeFragmentTestEnable;
} VkPipelineRepresentativeFragmentTestStateCreateInfoNV;-
sTypeis the type of this structure. -
pNextisNULLor a pointer to a structure extending this structure. -
representativeFragmentTestEnablecontrols whether the representative fragment test is enabled.
If this structure is not included in the pNext chain,
representativeFragmentTestEnable is considered to be VK_FALSE,
and the representative fragment test is disabled.
If the active fragment shader does not specify the EarlyFragmentTests
execution mode, the representative fragment shader test has no effect, even
if enabled.
28.12. Sample Counting
Occlusion queries use query pool entries to track the number of samples that pass all the per-fragment tests. The mechanism of collecting an occlusion query value is described in Occlusion Queries.
The occlusion query sample counter increments by one for each sample with a coverage value of 1 in each fragment that survives all the per-fragment tests, including scissor, exclusive scissor, sample mask, alpha to coverage, stencil, and depth tests.
28.13. Fragment Coverage To Color
The VkPipelineCoverageToColorStateCreateInfoNV structure is defined
as:
// Provided by VK_NV_fragment_coverage_to_color
typedef struct VkPipelineCoverageToColorStateCreateInfoNV {
VkStructureType sType;
const void* pNext;
VkPipelineCoverageToColorStateCreateFlagsNV flags;
VkBool32 coverageToColorEnable;
uint32_t coverageToColorLocation;
} VkPipelineCoverageToColorStateCreateInfoNV;-
sTypeis the type of this structure. -
pNextisNULLor a pointer to a structure extending this structure. -
flagsis reserved for future use. -
coverageToColorEnablecontrols whether the fragment coverage value replaces a fragment color output. -
coverageToColorLocationcontrols which fragment shader color output value is replaced.
If the pNext chain of VkPipelineMultisampleStateCreateInfo
includes a VkPipelineCoverageToColorStateCreateInfoNV structure, then
that structure controls whether the fragment coverage is substituted for a
fragment color output and, if so, which output is replaced.
If coverageToColorEnable is VK_TRUE, the
coverage mask replaces the first
component of the color value corresponding to the fragment shader output
location with Location equal to coverageToColorLocation and
Index equal to zero.
If the color attachment format has fewer bits than the coverage mask, the
low bits of the sample coverage mask are taken without any clamping.
If the color attachment format has more bits than the coverage mask, the
high bits of the sample coverage mask are filled with zeros.
If coverageToColorEnable is VK_FALSE, these operations are
skipped.
If this structure is not included in the pNext chain, it is as if
coverageToColorEnable is VK_FALSE.
// Provided by VK_NV_fragment_coverage_to_color
typedef VkFlags VkPipelineCoverageToColorStateCreateFlagsNV;VkPipelineCoverageToColorStateCreateFlagsNV is a bitmask type for
setting a mask, but is currently reserved for future use.
28.14. Coverage Reduction
Coverage reduction takes the coverage information for a fragment and converts that to a boolean coverage value for each color sample in each pixel covered by the fragment.
28.14.1. Pixel Coverage
Coverage for each pixel is first extracted from the total fragment coverage
mask.
This consists of rasterizationSamples unique coverage samples for each
pixel in the fragment area, each with a unique
sample index.
If the fragment only contains a single pixel, coverage for the pixel is
equivalent to the fragment coverage.
If the render pass has a fragment density map attachment and the fragment covers multiple pixels, pixel coverage is generated in an implementation-dependent manner. If all samples in the fragment are covered, all samples will be covered in each pixel coverage.
If a shading rate image is used, and the fragment covers multiple pixels, each pixel’s coverage consists of the coverage samples corresponding to that pixel, and each sample retains its unique sample index i.
If the fragment shading rate is set, and the fragment covers multiple pixels, each pixel’s coverage consists of the coverage samples with a pixel index matching that pixel, and each sample retains its unique sample index i.
28.14.2. Color Sample Coverage
Once pixel coverage is determined, coverage for each individual color sample corresponding to that pixel is determined.
If the
number of rasterizationSamples is identical to the number of samples
in the color attachments.
A color sample is covered if the pixel coverage sample with the same
sample index i is covered.
Otherwise, the coverage for each color sample is computed from the pixel coverage as follows.
If the VK_AMD_mixed_attachment_samples extension is enabled, for
color samples present in the color attachments, a color sample is covered if
the pixel coverage sample with the same
sample index i is covered;
additional pixel coverage samples are discarded.
If the pNext chain of VkSubpassDescription2
or VkRenderingInfo
includes a VkMultisampledRenderToSingleSampledInfoEXT structure with
the multisampledRenderToSingleSampledEnable field equal to
VK_TRUE, sample coverage is calculated as if the attachment has
VkMultisampledRenderToSingleSampledInfoEXT::rasterizationSamples
samples.
When the VK_NV_coverage_reduction_mode extension is enabled, the
pipeline state controlling coverage reduction is specified through the
members of the VkPipelineCoverageReductionStateCreateInfoNV structure.
The VkPipelineCoverageReductionStateCreateInfoNV structure is defined
as:
// Provided by VK_NV_coverage_reduction_mode
typedef struct VkPipelineCoverageReductionStateCreateInfoNV {
VkStructureType sType;
const void* pNext;
VkPipelineCoverageReductionStateCreateFlagsNV flags;
VkCoverageReductionModeNV coverageReductionMode;
} VkPipelineCoverageReductionStateCreateInfoNV;-
sTypeis the type of this structure. -
pNextisNULLor a pointer to a structure extending this structure. -
flagsis reserved for future use. -
coverageReductionModeis a VkCoverageReductionModeNV value controlling how color sample coverage is generated from pixel coverage.
If this structure is not included in the pNext chain, or if the
extension is not enabled, the default coverage reduction mode is inferred as
follows:
-
If the
VK_NV_framebuffer_mixed_samplesextension is enabled, then it is as if thecoverageReductionModeisVK_COVERAGE_REDUCTION_MODE_MERGE_NV. -
If the
VK_AMD_mixed_attachment_samplesextension is enabled, then it is as if thecoverageReductionModeisVK_COVERAGE_REDUCTION_MODE_TRUNCATE_NV. -
If both
VK_NV_framebuffer_mixed_samplesandVK_AMD_mixed_attachment_samplesare enabled, then the default coverage reduction mode is implementation-dependent.
// Provided by VK_NV_coverage_reduction_mode
typedef VkFlags VkPipelineCoverageReductionStateCreateFlagsNV;VkPipelineCoverageReductionStateCreateFlagsNV is a bitmask type for
setting a mask, but is currently reserved for future use.
Possible values of
VkPipelineCoverageReductionStateCreateInfoNV::coverageReductionMode,
specifying how color sample coverage is generated from pixel coverage, are:
// Provided by VK_NV_coverage_reduction_mode
typedef enum VkCoverageReductionModeNV {
VK_COVERAGE_REDUCTION_MODE_MERGE_NV = 0,
VK_COVERAGE_REDUCTION_MODE_TRUNCATE_NV = 1,
} VkCoverageReductionModeNV;-
VK_COVERAGE_REDUCTION_MODE_MERGE_NVspecifies that each color sample will be associated with an implementation-dependent subset of samples in the pixel coverage. If any of those associated samples are covered, the color sample is covered. -
VK_COVERAGE_REDUCTION_MODE_TRUNCATE_NVspecifies that for color samples present in the color attachments, a color sample is covered if the pixel coverage sample with the same sample index i is covered; other pixel coverage samples are discarded.
To query the set of mixed sample combinations of coverage reduction mode, rasterization samples and color, depth, stencil attachment sample counts that are supported by a physical device, call:
// Provided by VK_NV_coverage_reduction_mode
VkResult vkGetPhysicalDeviceSupportedFramebufferMixedSamplesCombinationsNV(
VkPhysicalDevice physicalDevice,
uint32_t* pCombinationCount,
VkFramebufferMixedSamplesCombinationNV* pCombinations);-
physicalDeviceis the physical device from which to query the set of combinations. -
pCombinationCountis a pointer to an integer related to the number of combinations available or queried, as described below. -
pCombinationsis eitherNULLor a pointer to an array of VkFramebufferMixedSamplesCombinationNV values, indicating the supported combinations of coverage reduction mode, rasterization samples, and color, depth, stencil attachment sample counts.
If pCombinations is NULL, then the number of supported combinations
for the given physicalDevice is returned in pCombinationCount.
Otherwise, pCombinationCount must point to a variable set by the user
to the number of elements in the pCombinations array, and on return
the variable is overwritten with the number of values actually written to
pCombinations.
If the value of pCombinationCount is less than the number of
combinations supported for the given physicalDevice, at most
pCombinationCount values will be written to pCombinations, and
VK_INCOMPLETE will be returned instead of VK_SUCCESS, to
indicate that not all the supported values were returned.
The VkFramebufferMixedSamplesCombinationNV structure is defined as:
// Provided by VK_NV_coverage_reduction_mode
typedef struct VkFramebufferMixedSamplesCombinationNV {
VkStructureType sType;
void* pNext;
VkCoverageReductionModeNV coverageReductionMode;
VkSampleCountFlagBits rasterizationSamples;
VkSampleCountFlags depthStencilSamples;
VkSampleCountFlags colorSamples;
} VkFramebufferMixedSamplesCombinationNV;-
sTypeis the type of this structure. -
pNextisNULLor a pointer to a structure extending this structure. -
coverageReductionModeis a VkCoverageReductionModeNV value specifying the coverage reduction mode. -
rasterizationSamplesis a VkSampleCountFlagBits specifying the number of rasterization samples in the supported combination. -
depthStencilSamplesspecifies the number of samples in the depth stencil attachment in the supported combination. A value of 0 indicates the combination does not have a depth stencil attachment. -
colorSamplesspecifies the number of color samples in a color attachment in the supported combination. A value of 0 indicates the combination does not have a color attachment.
28.14.3. Coverage Modulation
As part of coverage reduction, fragment color values can also be modulated (multiplied) by a value that is a function of fraction of covered rasterization samples associated with that color sample.
Pipeline state controlling coverage modulation is specified through the
members of the VkPipelineCoverageModulationStateCreateInfoNV
structure.
The VkPipelineCoverageModulationStateCreateInfoNV structure is defined
as:
// Provided by VK_NV_framebuffer_mixed_samples
typedef struct VkPipelineCoverageModulationStateCreateInfoNV {
VkStructureType sType;
const void* pNext;
VkPipelineCoverageModulationStateCreateFlagsNV flags;
VkCoverageModulationModeNV coverageModulationMode;
VkBool32 coverageModulationTableEnable;
uint32_t coverageModulationTableCount;
const float* pCoverageModulationTable;
} VkPipelineCoverageModulationStateCreateInfoNV;-
sTypeis the type of this structure. -
pNextisNULLor a pointer to a structure extending this structure. -
flagsis reserved for future use. -
coverageModulationModeis a VkCoverageModulationModeNV value controlling which color components are modulated. -
coverageModulationTableEnablecontrols whether the modulation factor is looked up from a table inpCoverageModulationTable. -
coverageModulationTableCountis the number of elements inpCoverageModulationTable. -
pCoverageModulationTableis a table of modulation factors containing a value for each number of covered samples.
If coverageModulationTableEnable is VK_FALSE, then for each
color sample the associated bits of the pixel coverage are counted and
divided by the number of associated bits to produce a modulation factor
R in the range (0,1] (a value of zero would have been killed due
to a color coverage of 0).
Specifically:
-
N = value of
rasterizationSamples -
M = value of VkAttachmentDescription::
samplesfor any color attachments -
R = popcount(associated coverage bits) / (N / M)
If coverageModulationTableEnable is VK_TRUE, the value R
is computed using a programmable lookup table.
The lookup table has N / M elements, and the element of the table is
selected by:
-
R =
pCoverageModulationTable[popcount(associated coverage bits)-1]
Note that the table does not have an entry for popcount(associated coverage bits) = 0, because such samples would have been killed.
The values of pCoverageModulationTable may be rounded to an
implementation-dependent precision, which is at least as fine as 1 /
N, and clamped to [0,1].
For each color attachment with a floating point or normalized color format,
each fragment output color value is replicated to M values which can
each be modulated (multiplied) by that color sample’s associated value of
R.
Which components are modulated is controlled by
coverageModulationMode.
If this structure is not included in the pNext chain, it is as if
coverageModulationMode is VK_COVERAGE_MODULATION_MODE_NONE_NV.
If the coverage reduction mode is
VK_COVERAGE_REDUCTION_MODE_TRUNCATE_NV, each color sample is
associated with only a single coverage sample.
In this case, it is as if coverageModulationMode is
VK_COVERAGE_MODULATION_MODE_NONE_NV.
// Provided by VK_NV_framebuffer_mixed_samples
typedef VkFlags VkPipelineCoverageModulationStateCreateFlagsNV;VkPipelineCoverageModulationStateCreateFlagsNV is a bitmask type for
setting a mask, but is currently reserved for future use.
Possible values of
VkPipelineCoverageModulationStateCreateInfoNV::coverageModulationMode,
specifying which color components are modulated, are:
// Provided by VK_NV_framebuffer_mixed_samples
typedef enum VkCoverageModulationModeNV {
VK_COVERAGE_MODULATION_MODE_NONE_NV = 0,
VK_COVERAGE_MODULATION_MODE_RGB_NV = 1,
VK_COVERAGE_MODULATION_MODE_ALPHA_NV = 2,
VK_COVERAGE_MODULATION_MODE_RGBA_NV = 3,
} VkCoverageModulationModeNV;-
VK_COVERAGE_MODULATION_MODE_NONE_NVspecifies that no components are multiplied by the modulation factor. -
VK_COVERAGE_MODULATION_MODE_RGB_NVspecifies that the red, green, and blue components are multiplied by the modulation factor. -
VK_COVERAGE_MODULATION_MODE_ALPHA_NVspecifies that the alpha component is multiplied by the modulation factor. -
VK_COVERAGE_MODULATION_MODE_RGBA_NVspecifies that all components are multiplied by the modulation factor.