[rakefire-impala]

Rebase of #477 by @imbahzor onto current main, as asked when it was closed ("please rebase on current main and reopen"). The commit is theirs, cherry-picked with -x; the only changes are the conflict resolution and the push-descriptor mark, which now goes through main's descriptors_disturbed() (see Change).

Problem

Over sunlit ground and along shadow edges near trees, shadows flicker constantly in thin streaks, even with the camera still. This happens on GPUs where the gameplay TAAU network is left out ("a network left out on this card" in the log, for example an RX 5500M), so the bilinear stand-in runs instead.

The tree-shadow pass 3427a1dbefd5e02c is a full-screen draw. It rebuilds a normal from an ImageGather of the neighbouring depths and offsets its shadow-map lookup by that normal. On grass blades and leaf edges, those neighbours flip between the blade and the ground behind it as the camera shifts by a sub-pixel each frame, so the pixels flip between lit and shadowed. On the console, the TAAU network averages that away.

Change

• Mask history. Right after that draw, its mask (G and B of an RGBA8 target at the scene's size, MIN blended) is blended with its own history in a small compute pass, shaders/shadow_stab.comp: two history images used in turn, then G and B copied back.
  • RX_VK_MASK_BLEND=<w>: the weight, default 0.85; 0 turns it off.
  • RX_VK_MASK_RADIUS=<r>: limits the history to a (2r+1)² neighbourhood. Default 0 (no limit), because a 3×3 limit kept nothing.
• Push-descriptor cache. The new pass pushes descriptors of its own layout, so it calls descriptors_disturbed() right after the push. Without that, the next dispatch with the cached layout skipped its push and read the pass's bindings, which caused a device lost after a save load in vk: tree-shadow flicker evened out; push-descriptor cache stale after the stand-ins' pushes #477's testing. vk: tree-shadow flicker evened out; push-descriptor cache stale after the stand-ins' pushes #477 also marked movie_upscale and taau_stand_in; main now does that itself.

Tests

tests/test_tree_shadow_mask.py (new) checks that the blend follows the tree-shadow pass only while RX_VK_MASK_BLEND is above 0, needs an RGBA8 storage mask and push descriptors, runs outside the render pass, and that every push of the stand-ins' or the mask's own layout reaches descriptors_disturbed() before its function returns. It fails with any one of those three calls removed.

Tested

• vk: tree-shadow flicker evened out; push-descriptor cache stale after the stand-ins' pushes #477 (author): RTX 3060, Windows 11. No flicker standing still, and no visible smearing of tree shadows when turning or walking, in Kokiri Forest and the Lost Woods at several times of day.
• First rebase (main 779bdcf): played on an RX 5500M (RDNA1, 4 GB, Windows 11, AMD driver; main 779bdcf with fix(vk): rainbow block-noise textures on low-VRAM cards: a failed BC3 upload is tried again, not drawn as noise #1505–fix(vk): texture noise when system RAM runs low: a staging arena of the size needed when 64 MB can't be pinned #1514) in Hyrule Field. The constant shadow flicker is gone. The log shows tree-shadow mask blend on #266 768x432, weight 0.85; the pass runs once a frame there.
• GTX 1070 (CiLiBi18, main 88b554e with fix(vk): mesh fallback flicker: wait for the last draw before clearing the shared buffers (#1383 review) #1509–fix(vk): coloured specks on fallback foliage (AMD): the generated vertex stage's outputs start at (0,0,0,1) #1513 and this PR): no flicker, specks or tree-shadow problems noticed in a 23-minute session; see their comment on fix(vk): missing floor grass without mesh shaders: indirect task draws ran no mesh workgroups #1510.
• Rebased on main 9447e1d: one conflict, the renamed skin_check call next to the new guard. Compile check clean. tests/run_all.py: 291 passed; the 6 that fail are the same 6 that fail on plain main on this PC, so no new failures. Not played again: the only code change from the played version is the push-descriptor mark going through descriptors_disturbed().

[rakefire-impala]

Rebased on main 9447e1d. The only conflict was the line just before the new guard in draw(): dlss_skin_check is skin_check on main now.

One more change came with the rebase. Main now calls descriptors_disturbed() after movie_upscale and taau_stand_in push their own descriptors, so this PR's marks there are gone, and the new pass uses that helper too. The test checks that all three pushes reach it and fails with any one removed.

I also fixed your first nit: the header comment of shadow_stab.comp now says the history is unbounded by default. It's a comment-only change, so the SPIR-V is unchanged. I left the other two nits alone so the code stays as you reviewed it. #1637 and #1776 are both in main already, and this merges on top of them.