Merge pull request #3228 from GustavoGamarra95/feat/agc-alpha-to-coverage

feat(agc): emulate undithered alpha-to-coverage

docs/dev/TechnicalDebt.md

@@ -121,6 +121,7 @@ Throughout the project, every function at every stage either **does exactly what
 - [libSceVdecsw](../../core/libs/prx/libSceVdecsw/Export.cpp) (libSceVdecsw) - structure layouts follow shadPS4's `vdecsw.h` and were checked against PPSA05684's movie decoder (`movie-decoder-vdecsw.cpp`), which asserts `pictureCount == 1` at offset 0xb of `OutputInfo` and reads `InputResult` offset 0x10 as the number of frames an access unit produced. The compute, decoder memory and decode input structures and the first 0x28 bytes of the 0x50-byte decoder config are those of libSceVideodec2, and decoding goes through it. The 0x78-byte AVC picture info is filled with Videodec2's leading fields and the cropping fields only. OUTPUT_PENDING (0x81510115), INPUT_QUEUE_EMPTY (0x81510116) and DECODE_PENDING (0x81510117) follow from the codes each call's assert accepts. At most four decoded pictures are queued and the last one is held until `sceVdecswFinalizeDecodeSequence`; the console's queue depth is unknown
 - [sceGameLiveStreamingGetCurrentStatus2](../../core/libs/prx/libSceGameLiveStreaming/Export.cpp) (libSceGameLiveStreaming) - the status layout (user id, on-air flag, spectator, text and command message counts, broadcast resolution, 48 reserved bytes) is taken from shadPS4's `OrbisGameLiveStreamingStatus2`; the call reports that no stream is on air, with an invalid user id
 - [Depth clear draws](../../core/libs/prx/libSceAgcDriver/Graphics/src/State.cpp) (AGC driver) - a draw with `DB_RENDER_CONTROL.DEPTH_CLEAR_ENABLE` is taken to write `DB_DEPTH_CLEAR` to every pixel it covers whatever the depth test, depth bounds and depth bias say: it is drawn with an always-passing depth write and the viewport depth range pinned to the clear value. The draw is rasterized as submitted, so its coverage is the draw's own. Whether the DB still applies the depth test or HiZ to such a draw is not measured
+- [Alpha-to-coverage](../../core/libs/prx/libSceAgcDriver/Graphics/src/State.cpp) (AGC driver) - only `DB_ALPHA_TO_MASK = 0xaa01` is accepted: the enable bit with the four quad offsets at 2 and no `OFFSET_ROUND`, the undithered setting [radeonsi](https://gitlab.freedesktop.org/mesa/mesa/-/blob/bffd91947efc1932da99aca69fc540d6d4201b0c/src/gallium/drivers/radeonsi/si_state.c#L371-L381) programs. Draws are single-sampled, so the pixel shader [writes](../../core/shader/recompiler/SpirvBackend/src/SpirvModuleEmitter.cpp) `SampleMask` 0 when its MRT0 alpha is below one half or NaN and all ones otherwise, and runs with late fragment tests. That rule was measured on a Radeon 660M (gfx1035, RADV with `RADV_DEBUG=noatocdithering`, which programs the same register) for 0, -0, 0.25, the two floats below one half, one half, the two above, 0.75, 1, 2, -1, both infinities and both NaNs, and is pinned in [AlphaToCoverage.cpp](../../core/libs/prx/libSceAgcDriver/tests/execution/AlphaToCoverage.cpp); it is not measured on gfx1013. Vulkan's `alphaToCoverageEnable` is not used: the NVIDIA driver 615.78.08 dithers single-sample coverage (an alpha of 0.25 writes half the pixels of an RTX 3050 Laptop target). Other offsets, `OFFSET_ROUND`, a sample-mask export, and an MRT0 that is missing, swizzled, packed or exported without a floating-point alpha throw
 - [GPU flips](../../core/libs/prx/libSceVideoOut/src/VideoOutDriver.cpp) (libSceVideoOut) - a command-buffer flip of a buffer index with no registered buffer when the GPU reaches it presents black and completes like any flip (flip event, count, `flipPendingNum`). The console's behaviour is unknown; PPSA05684 requires that it completes: its renderer submits a flip of buffer 0 while another thread waits for `sceVideoOutIsFlipPending` to reach 0 before registering the buffers, and `flipPendingNum` counts that flip from its submission as in shadPS4
 - [sceAgcDriverGetEqContextId](../../core/libs/prx/libSceAgcDriver/Eq/src/Query.cpp) (libSceAgcDriver) - returns `ident`: an end-of-pipe interrupt is delivered only to the registration whose id equals the raising queue, so `ident` is that context's id (titles register 0 or 1 for graphics and `0x20 + 8 * pipe + queue` for compute). The console's value is not known; KytyPS5 returns the event's `data`, which it fills with the interrupt's context id, whereas `data` here is the EV_CLEAR trigger count. Other event filters throw
 - [sceAgcSetSubmitMode](../../core/libs/prx/libSceAgc/Misc/src/Suspend.cpp) (libSceAgc) - mode values unknown; only 0 is accepted