XXX - Not complete yet!!!
Name
SGIX_quad_mesh
Name Strings
GL_SGIX_quad_mesh
Version
$Date: 1997/02/21 17:32:24 $ $Revision: 1.2 $
Number
XXX
Dependencies
No extensions are required.
OpenGL 1.1 and EXT_vertex_array affect the definition of this extension.
Overview
This extension adds two primitive types, the quadrilateral mesh and the
line mesh.
For datasets representing from manifold surfaces, such as NURBS surfaces
and most triangular databases, quadrilateral meshes reduce the number of
vertices which must be transferred from the host to the graphics hardware
by up to fifty percent. This also reduces by fifty percent the number of
vertices which must be clipped and lit.
Quad and line meshes also reduce by half the number of vertices which must
be transformed and lit.
Issues
* Kurt: The issue in the past has been the required intermediate storage.
Your spec seems to require that implementations be able to store at least
512 vertexes. I wonder how you arrived at this number.
Matt: I chose this number primary because it is large enough that
applications are unlikely to have quad-mesh datasets larger than this
size. I wanted to avoid forcing applications to carve up their quad mesh
data in hardware-specific ways, and instead allow the implementation to
make the decision about optimal mesh width.
I was also careful to minimize the amount of state. Note that a naive
implementation that just wants to draw the quad mesh as a bunch of
independent quads only needs to amount of state listed in the spec.
Every time glVertex is then called, one new quad is drawn.
* Kurt: Is it implementable on all current SGI platforms?
Matt: If it is implemented as drawing independent quads, then yes. On
platforms where you really want to take advantage of the fact that you can
light and xform the shared vertices only once, you may need to carve up
the quad mesh into smaller pieces on the host (or ge). to do that, you
will need more implementation-private state.
New Procedures and Functions
void MeshBreadthSGIX(int breadth);
void MeshStrideSGIX(int stride);
New Tokens
Accepted by the parameter of Begin, and
also accepted by the parameter of DrawArrays:
QUAD_MESH_SGIX 0x????
LINE_MESH_SGIX 0x????
Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)
Append to section 2.6.1 (Begin and End Objects):
Quad meshes and line meshes use an auxilliary function, MeshBreadthSGIX to
define GL state which affects the quads and lines drawn by these
primitives. The parameter to MeshBreadthSGIX is used in the
descriptions of quad meshes and line meshes below.
Quadrilateral (quad) meshes:
Quad meshes efficiently generate a series of quads in a regular grid.
Given n input vertices to the quad mesh, the last n mod vertices
are ignored completely. Let length = (n - (n mod )) / ,
and consider all j = 0,1,2,*length-1. A quad is drawn for four
vertices v_j--1, v_j-, v_j, v_j-1 for all j such that j
mod != 0 and j >= . The order in which the quads
within a quad mesh are drawn is intentionally left completely undefined.
Line meshes:
Line meshes efficiently generate a series of lines in a regular grid.
Given n input vertices to the line mesh, the last n mod vertices
are ignored completely. Let length = (n - (n mod )) / ,
and consider all j = 0,1,2,*length-1. A line is drawn between
vertex v_j-1 and v_j for all j such that j mod != 0. A line is
drawn between vertex v_j- and v_j for all j such that j >=
. The order in which the lines within a line mesh are drawn is
intentionally left completely undefined.
Append to section 2.8 (Vertex Arrays) entry for DrawArrays:
The order in which the quads or lines within a quad mesh or line mesh are
drawn is intentionally left completely undefined. They may be rendered in
any order convenient for the implementation.
Additions to Chapter 3 of the 1.0 Specification (Rasterization)
None
Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations
and the Frame Buffer)
None
Additions to Chapter 5 of the 1.0 Specification (Special Functions)
None
Additions to Chapter 6 of the 1.0 Specification (State and State Requests)
None
Additions to the GLX Specification
None
GLX Protocol
XXX - Not figured out yet.
Dependencies on OpenGL 1.1
Dependencies on EXT_vertex_array
If neither OpenGL 1.1 nor EXT_vertex_array are present, then the following
should be omited:
all references to MeshStrideSGIX,
all references to DrawArrays.
Errors
INVALID_VALUE is generated if MeshBreadthSGIX parameter is
zero or negative.
INVALID_OPERATION is generated if MeshBreadthSGIX is executed between the
execution of Begin and the corresponding execution of End.
New State
Replace beginning of table 6.4: GL Internal begin-end state variables (inaccessible)
Get Value Get Command Type Value Attrib Description
--------- ----------- ---- ------- ------ -----------
Z_13 0 When != 0, indicates begin/end object
Append to table 6.4: GL Internal begin-end state variables (inaccessible)
Get Value Get Command Type Value Attrib Description
--------- ----------- ---- ------- ------ -----------
513*XV MAX_MESH_BREADTH + 1 vertices.
First entries are from current row.
Last entries are from previous row.
Z512* 0 Number of vertices accumulated for
current row of mesh in the array above.
B 0 True if not in first row of quad mesh.
Append to table 6.5: Current Values and Associated Data
Get Value Get Command Type Value Attrib Description
--------- ----------- ---- ------- ------ -----------
MESH_BREADTH glGetIntegerv Z+ 2 current Breadth of quad and line meshes
New Implementation Dependent State
Get Value Get Command Type Value Attrib
--------- ----------- ---- ------- ------
MAX_MESH_BREADTH glGetIntegerv Z+ 512*