kc3-lang/angle

2019-05-06T14:55:18

Vulkan: Implement EXT_draw_buffers In GLES, color attachments are referenced by their indices. These indices match between the API and GLSL. For example, if a shader has: layout(location=0) out color; layout(location=3) out roughness; Then GLES would bind and enable GL_COLOR_ATTACHMENT0 and GL_COLOR_ATTACHMENT3. In Vulkan, the framebuffer object and the corresponding renderpass define the color attachments, and they don't allow gaps in color attachments as GLES does. A render subpass creates the mapping between the color attachments as defined in the framebuffer and the attachments used by the shader (with possible gaps). This change packs the enabled GL color attachments for the sake of the framebuffer, and sets the subpass up in such a way that the shaders continue to use the same color output indices as GLES. In the example above, we have the attachment indices as follows: Status | GLES | GLSL | RenderPass | Subpass enabled 0 0 0 0 disabled 1 - VK_ATTACHMENT_UNUSED disabled 2 - VK_ATTACHMENT_UNUSED enabled 3 3 1 1 That is, the array of color attachments in the Vulkan framebuffer/renderpass is: [0] = GL color attachment 0 [1] = GL color attachment 3 And the array of color attachment references in the Vulkan render subpass is: [0] = 0 (index 0 of the renderpass attachment array) [1] = VK_ATTACHMENT_UNUSED [2] = VK_ATTACHMENT_UNUSED [3] = 1 (index 1 of the renderpass attachment array) Bug: angleproject:2394 Change-Id: Ib6cd2b60882643ea152986eee453270d09cd4aed Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1595442 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>