kc3-lang/angle

2020-09-07T23:07:37

Vulkan: Use subpass to unresolve render-to-texture attachments GL_EXT_multisampled_render_to_texture allows singlesampled textures to be used with multisampled framebuffers in such a way that the final resolve operation is automatically done. In Vulkan terminology, the render-to-texture GL attachment is used as a Vulkan subpass resolve attachment with an implicit (ideally-)lazy-memory multisampled image as the color attachment. This extension expects that if the texture is drawn to after the automatic resolve, the implicit multisampled image would take its fragment colors from the singlesampled image. In other words, the opposite of a resolve operation should be automatically performed at the start of the render pass. This change refers to this operation as "unresolve". The goal of this extension is to allow tiling GPUs to always keep multisampled data on tile memory and only ever load/store singlesampled data. The latter is achieved by using a subpass resolve attachment and setting storeOp of the multisampled color attachment to DONT_CARE. This change achieves the former by using an initial subpass that uses the resolve attachment as input attachment, draws into the multisampled color attachment and sets loadOp of said attachment to DONT_CARE. Bug: angleproject:4881 Change-Id: I99f410530365963567c77a7d62fc9db1500e5e3e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2397206 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>