C Specification

The supportedCompositeAlpha member is of type VkCompositeAlphaFlagBitsKHR, which contains the following values:

typedef enum VkCompositeAlphaFlagBitsKHR {
    VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR = 0x00000001,
    VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR = 0x00000002,
    VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR = 0x00000004,
    VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR = 0x00000008,
    VK_COMPOSITE_ALPHA_FLAG_BITS_MAX_ENUM_KHR = 0x7FFFFFFF
} VkCompositeAlphaFlagBitsKHR;

Description

These values are described as follows:

  • VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR: The alpha channel, if it exists, of the images is ignored in the compositing process. Instead, the image is treated as if it has a constant alpha of 1.0.

  • VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR: The alpha channel, if it exists, of the images is respected in the compositing process. The non-alpha channels of the image are expected to already be multiplied by the alpha channel by the application.

  • VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR: The alpha channel, if it exists, of the images is respected in the compositing process. The non-alpha channels of the image are not expected to already be multiplied by the alpha channel by the application; instead, the compositor will multiply the non-alpha channels of the image by the alpha channel during compositing.

  • VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR: The way in which the presentation engine treats the alpha channel in the images is unknown to the Vulkan API. Instead, the application is responsible for setting the composite alpha blending mode using native window system commands. If the application does not set the blending mode using native window system commands, then a platform-specific default will be used.

See Also

Document Notes

For more information, see the Vulkan Specification

This page is extracted from the Vulkan Specification. Fixes and changes should be made to the Specification, not directly.

Copyright (c) 2014-2019 Khronos Group. This work is licensed under a Creative Commons Attribution 4.0 International License.