Legacy color-key contract evidence

Verified 2026-10-15 against preserved original Microsoft DirectX SDK pages.

The DX7 D3DRENDERSTATETYPE reference identifies COLORKEYBLENDENABLE as state 144. When explicitly enabled, matching texture samples have both color and alpha replaced by zero. The application configures alpha testing and blending to obtain rejection or blending. This entry does not specify the initial value, the disabled-mode filtering algorithm, or precedence with alpha-capable palettes.

The DX7 Color Keying State page, dated September 2, 1999, specifies FALSE as the default of COLORKEYENABLE (state 41). That is not evidence for state 144's default.

Implementation consequences

The candidate in task/palette-worker-lifetime still retains keyed RGB while clearing alpha during GPU upload. Its shared fixed-function shader discards samples below alpha 0.5 regardless of the application's alpha-test settings. These operations do not implement the documented explicitly enabled state144 mode. Both software and GPU paths need to consume that state, retain its identity in relevant descriptors/caches, and test actual framebuffer results.

Do not infer universal rejection whenever any filtered tap matches a key. Default/FALSE behavior, zero-weight and border taps, and DDPCAPS_ALPHA/key precedence remain unresolved. Existing unkeyed palette GPU/Worker passes do not cover these contracts. No production behavior changes or native reference measurements accompany this note.