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Hash : 9475ac40
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Date : 2023-11-15T10:25:06
Vulkan: Make efficient MSAA resolve possible Prior to this change, using a resolve attachment to implement resolve through glBlitFramebuffer was done by temporarily modifying the source FramebufferVk's framebuffer description. This caused a good deal of complexity; enough to require the render pass to be immediately closed after this optimization. The downsides to this are: - Only one attachment can be efficiently resolved - There is no chance for the MSAA attachment to be invalidated In this change, resolve attachments that are added because of glBlitFramebuffer are stored in the command buffer, with the FramebufferVk completely oblivious to them. When the render pass is closed, either the FramebufferVk's original framebuffer object is used (if no resolve attachments are added) or a temporary one is created to include those resolve attachments. With the above method, the render pass is able to accumulate many resolve attachments as well as have its MSAA attachments be invalidated before it is flushed. For a FramebufferVk that is resolved in this way, there used to be two framebuffers created each time and thrown away as the code alternated between starting a render pass without a resolve attachment and then closing with one. With this change, there is now one framebuffer (without resolve attachments) that is cached in FramebufferVk (and is not recreated every time), and only the framebuffer with resolve attachments is recreated every time. Ultimatley, when VK_KHR_dynamic_rendering is implemented in ANGLE, there would be no framebuffers to create and destroy, and this change paves the way for that support too. WindowSurfaceVk framebuffers are still imagefull. Making them imageless adds unnecessary complication with no benefit. ----------------- To achieve efficient MSAA rendering on tiling hardware, applications should do the following: ``` glBindFramebuffer(GL_FRAMEBUFFER, msaaFBO); // Clear the framebuffer to avoid a load // Or invalidate, if not needed to load: // glInvalidateFramebuffer(GL_DRAW_FRAMEBUFFER, ...); glClear(...); // Draw calls // Resolve into the single sampled framebuffer glBindFramebuffer(GL_DRAW_FRAMEBUFFER, resolveFBO); glBlitFramebuffer(...); // Immediately discard the contents of the MSAA buffer, to avoid store glInvalidateFramebuffer(GL_READ_FRAMEBUFFER, ...); ``` The above would translate to the following Vulkan render pass: - MSAA LOAD_OP_CLEAR/DONT_CARE - MSAA STORE_OP_DONT_CARE - Resolve LOAD_OP_DONT_CARE - Resolve STORE_OP_STORE This makes sure the MSAA data doesn't leave the tile memory and greatly reduces bandwidth usage. Once anglebug.com/4892 is fixed, this would also allow the MSAA image to never be allocated either. Bug: angleproject:7551 Bug: angleproject:8625 Change-Id: Ia9f4d20863d76a013d8495033f95c7b39f77e062 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5388492 Reviewed-by: Yuxin Hu <yuxinhu@google.com> Reviewed-by: Amirali Abdolrashidi <abdolrashidi@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
