Final legacy mip filter bits

Audited fetched main a1704200c21b6e5a961d0d39093609891956f489. Both remaining advertised mip bits are unsupported. The only production change is fill_primcaps.dwTextureFilterCaps: F3 → C3, clearing 0x10 and 0x20. DX7 descriptor builders inherit 030003C3. Other fields and bits are unchanged. Existing exact-mask tests are reconciled, including the previous mip suite.

Exact legacy meanings

The retained Microsoft SDK d3dcaps.h lines 251–252 and d3dtypes.h lines 985–986 identify these constants (copies and hashes in the evidence). They came from Microsoft's win32metadata generation/WinSDK/RecompiledIdlHeaders/um/ directory, retained by the preceding audit, not from modern stage filter enums.

The semantic distinction is documented in Microsoft's D3DPRIMCAPS contract and archived D3DPRIMCAPS documentation. In particular, LINEARMIPNEAREST is not bilinear filtering within one level.

Implementation and evidence

In src/09ab-handlers-d3dim-core.wat, both the filter selection in d3dim_draw_tl_triangle_textured and d3dim_gpu_describe recognize only value 2 as linear. With stage MAG/MIN and legacy MAG unset, legacy MIN values 5 and 6 produce linear=0. d3dim_texture_sample_keyed then fetches a point from its single supplied image; its interface carries neither a second mip image nor an LOD interpolation weight. Its actual fetch/decode helpers read that image. lib/d3dim-gpu.js lowers the descriptor to point min/mag with mip: 0. Neither path performs the required between-level interpolation; value 6 also lacks the required within-level bilinear sampling.

node test/test-legacy-final-mip-bits.js executes extracted production WAT: filter selection, descriptor filter writes, sampler, address helper, bilerp, keyed/prepared fetch, format decoder and expand helpers. It also executes the actual JavaScript sampler assignment. No hand-written pixel-fetch implementation stands in for the production code.

The 36 state cases cover legal stage point/linear controls and legacy point/linear/5/6, at each fallback source with stage MIPFILTER 0/1/2. The legacy MIN-only cases explicitly reach values 5 and 6. Each case samples real memory containing a 4x4 black/white checkerboard and a separately bound 2x2 red/blue checkerboard. Controls yield the expected point or bilinear colors; 5/6 yield point colors. These are separately bound images, not a harness that invents mipchain selection or derivatives.

There are 90 descriptor-field checks through the actual builders and extracted GetCaps 1/2/3/7 handlers, covering both primitive types, HAL/HEL, sizes, alignment, return/stack effects and bounds guards. Enumeration-to-builder wiring is asserted; callbacks are not run.

Ten mutation controls reject each re-advertised bit separately, both together, lost point/linear support, unrelated bit clearing, enabled GPU mip filtering, software recognition of each value 5/6 as linear, and broken production pixel loads. The unchanged main baseline passes backend observations and fails on the advertised 0x10 bit. Separate 0x20-only re-advertising proves that bit is independently rejected, too.

The four existing source suites pass after exact-mask reconciliation; their old reviews are not reopened. Native enumeration is syntax-checked only. This is extracted-source evidence, not a canonical build, full VM, native COM, callback/lifetime, complete draw, actual GPU render, automatic mipchain, or game qualification. No runtime, Boat, browser, worker or main merge was used.

Self-contained snapshot, baseline, replay, logs, provenance and hashes: scratch/runs/20261020-legacy-final-mip-bits/.