feat: add alpha channel blending support#7
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- Add 'a' field to ZBufferPoint (8.16 fixed-point, same as r,g,b) - Propagate vertex alpha from glColor4f through the vertex pipeline - Add GL_SRC_ALPHA / GL_ONE_MINUS_SRC_ALPHA blend factors to TGL_BLEND_FUNC and TGL_BLEND_FUNC_RGB macros - Use TGL_ALPHA_MUL helper with (factor + factor>>7) correction to map [0,255] -> [0,256], ensuring alpha=255 is identity and alpha=0 produces exactly zero (no darkening artifacts) - Preserve texture alpha through RGB_MIX_FUNC in 32-bit mode - Add INTERP_A support to ztriangle.h for per-vertex alpha interpolation - Update smooth-shaded blend triangles to interpolate and use alpha - Update flat-shaded blend triangles to pack vertex alpha into pixel - Update line/point blend paths to pass alpha
- Add gl_convertRGBA_to_8A8R8G8B() that preserves the alpha channel when converting from RGBA byte data to internal 0xAARRGGBB format - Add gl_resizeImageNoInterpolate4() for resizing 4-channel textures - Update glopTexImage2D to accept GL_RGBA with components=4 - Texture alpha is preserved through TGL_BLEND_FUNC via the pixel's high byte, enabling proper alpha-blended textured geometry
Add 7 tests covering alpha channel rendering correctness: Untextured: - alpha_zero_transparent: alpha=0 produces fully transparent output - alpha_full_opaque: alpha=1 produces fully opaque output - alpha_half_blend: alpha=0.5 produces correct 50/50 blend - alpha_smooth_interp: GL_SMOOTH interpolates alpha per-vertex Textured (GL_RGBA): - alpha_texture_transparent: RGBA texture with alpha=0 is invisible - alpha_texture_opaque: RGBA texture with alpha=255 is fully visible - alpha_texture_half_blend: RGBA texture with alpha=128 blends correctly All tests use direct framebuffer readback and verify pixel values with a small tolerance for fixed-point rounding.
Owner
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Please provide sample programs to illustrate the use of newly-introduced APIs. |
tslmy
marked this pull request as ready for review
May 20, 2026 14:46
Author
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@jserv good idea. Added a |
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afield toZBufferPoint(8.16 fixed-point, same asr,g,b)glColor4fthrough the vertex pipelineGL_SRC_ALPHA/GL_ONE_MINUS_SRC_ALPHAblend factors toTGL_BLEND_FUNCandTGL_BLEND_FUNC_RGBmacrosTGL_ALPHA_MULhelper with (factor + factor>>7) correction to map[0,255]->[0,256], ensuringalpha=255is identity andalpha=0produces exactly zero (no darkening artifacts)RGB_MIX_FUNCin 32-bit modeINTERP_Asupport toztriangle.hfor per-vertex alpha interpolationAdded tests, for both textured and untextured models, to ensure that alpha blending works correctly.
Also added a compilable demo,
examples/raw/alpha.c, to illustrate how transparency may look like. It renders a scene like the image below:closes #6
Disclaimer: Coding agent (GitHub Copilot + Claude Sonnet 4.6) is heavily used in this PR.