A sprite that reads what it draws goes through the texture cache pixel by
pixel: rows left to right, top to bottom, texture lines loaded as samples
first read them, and pixels reaching memory a 16-byte block at a time, a
pixel after the next block starts (four with bilinear filtering). Fitted to
geprobe exp81 and exp204-exp209 on hardware; Split Second's blur passes now
match the PSP.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
The GE caches DXT1/3/5 lines as 8888 texels (geprobe exp203), sharing tags
with 8888 lines. A DXT primitive with stale lines is drawn from 8888 decodes
of its levels with those lines laid over them.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Measured on hardware (ppsspp-re geprobe exp177-202, docs/ge-texture-cache.md): 64 lines of 16 bytes x 8
rows in 16 sets of 4 ways, LRU, the set index split between column and band bits by texel size. A line is
tagged by its position in the texture and its mip level only, so another texture read without TEXFLUSH
gets the first one's bytes where their lines coincide; lines load raw bytes on first read and nothing but
TEXFLUSH drops them, not rendering into the texture, block transfers or CPU writes.
TexCache steps every textured primitive through that, in submission order, from its texel footprint. A
line remembers where it came from and its bytes are copied only before that memory changes (drawing, block
transfers, copies, and anything at all when the CPU is about to run). While every line is from the one
texture read since TEXFLUSH and nothing has been copied, nothing read can differ from memory, so primitives
only log what they read, and TEXFLUSH usually drops the log unread. A primitive that reads bytes differing
from memory, or draws over what it reads, is drawn alone from its texture with what it read from the cache
laid over memory. That replaces SelfTextureSnapshot and its "fits in 8 KB" rule.
All the cache experiments match the PSP exactly except exp177, which samples a block transfer's
destination without TEXSYNC. Within a primitive this still loads every line before it draws; the GE loads
them as it rasterizes (serpentine rows, writes reaching memory a 16-byte block late), which Split
Second's blur (the one dump that changes) depends on. About 2% slower in Tekken 6 and God of War.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
