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Texture Lab - addressing, transparency, palettes and texture LOD

Texture Lab: ESP32-style screenshot, performance overlay hidden

A labelled console cycles through seven stages, seven seconds each (49 seconds per loop), using the shared ESP32 scanout and FPS/MS/TRIS/TRI-S overlay.

Stage What to watch
WRAP The arrow tile repeats as the same UV rectangle scrolls beyond the image edges.
CLAMP The same animation stretches the coloured edge texels instead.
ZERO + black key Out-of-range UVs return black; black is keyed transparent, revealing the checker behind the panel.
Colour key Two panels share one palm image. The left retains its magenta background; the right keys it out.
Palette cycling A fixed 64x64 index image animates by shifting a 64-colour lava palette lookup.
LOD OFF The panel moves away and back; its texture stays enabled throughout.
LOD ON The exact same distance sweep fades the texture into a solid material colour, then restores it.

Texture LOD is not mipmapping or mesh LOD. Jet's textureLodNear=1100 and textureLodFar=1650 control a per-triangle depth-based crossfade to the material colour. The panel travels from Z=850 to Z=1900 and back. At the far endpoint the unlit fast path fills solid spans without per-pixel texture sampling. The fade band still samples and blends the texture. Changes in panel screen area also affect render time; compare corresponding points in the two matched sweeps.

ZERO addressing alone returns colour zero; transparency requires hasAlpha=true and alphaColor=0. The palm uses magenta (0xf81f) as its key. These are hard cut-outs, not smoothly blended alpha edges.

Palette pixels and colour entries remain immutable in flash. Only paletteOffset changes, at 18 steps/second based on absolute stage time, so animation does not depend on frame-rate rounding. The lava needs 4 KiB of indices plus 128 bytes of palette, with no rewritten pixel buffer or extra animation frames.

Rendering configuration

All geometry is unlit and nearest-sampled. Textured panels face the camera and each has constant depth across its surface, so affine UV interpolation is exact. Perspective correction, bilinear filtering and lighting are compiled out here; their appearance/performance comparisons live in the preceding examples.

Painter rendering uses no depth buffer. The console/backdrop occupy the background band and the demonstration cards the foreground band, keeping receding LOD panels visible within the console. This is a deliberately layered presentation, not a general arbitrary-geometry occlusion scheme. The two keyed cards never overlap.

The HUD retains full panel resolution over half-width alternating fields. FPS counts displayed fields; MS includes scene setup and both raster workers; TRI/S uses actual render time rather than the 60 Hz pacing interval. Values can briefly span two stages during a switch. See validation.

Build and validate

From an ESP-IDF 6.0.x terminal in this directory:

idf.py -B build-s3 "-DIDF_TARGET=esp32s3" "-DSDKCONFIG=sdkconfig.s3" build
idf.py -B build-s3 "-DIDF_TARGET=esp32s3" "-DSDKCONFIG=sdkconfig.s3" -p PORT flash monitor

Use the reference wiring. P4 defaults are included but this example is validated on S3 only.

With CMake and a C++17 compiler (use a developer prompt for MSVC):

cmake -S tests -B build-preview -DCMAKE_BUILD_TYPE=Release
cmake --build build-preview --config Release
ctest --test-dir build-preview -C Release --output-on-failure

The test emits texture-lab.ppm with eight views, including both fading and flat LOD states. Preview counters remain unmeasured; hardware supplies timing figures. Generated asset/label headers are checked in. Regenerate them with Pillow and python tools/prepare_assets.py, optionally passing --font path/to/font.ttf.