[pvcraven]

Summary

Fixes #2909: on WebGL, a SpriteList whose storage was created with a capacity over 256 only drew its first 256 sprites.

The problem

On WebGL, sprite data is stored in textures (SpriteListTextureData) instead of buffers:

• The shader reads them as rows of 256 sprites (lib/sprite.glsl: texelFetch(..., ivec2(index % 256, index / 256), 0)), and so does the GPU collision shader.
• The grow_* methods resize them to (256, rows).
• __init__ created them as one row as wide as the capacity. So with a capacity over 256, sprite i >= 256 was read from row i // 256, which didn't exist.

That happens with:

• SpriteList(capacity=1000);
• clear() on a list that had grown past 256 sprites, since it keeps the capacity and creates the storage again;
• a lazy list, or a list created before the window, with more than 256 sprites before it's first drawn.

The fix

Create the five textures as (256, capacity // 256), the layout the shader reads and the grow methods keep. The capacity is always a multiple of 256, and I align it anyway in case a subclass passes one that isn't. Uploads are whole-texture, row-major writes, so they don't change.

Verified

I reproduced it on desktop OpenGL by making SpriteList use the WebGL storage, drawing 1-pixel sprites into a framebuffer, and counting lit pixels:

Case	Before	After
Created at 256, grown by appending	600 / 600	600 / 600
Created at capacity 1024	256 / 600	600 / 600
Grown past 256, clear(), then 400 more	256 / 400	400 / 400

Tests

New tests/unit/spritelist/test_spritelist_texture_storage.py. It runs on desktop GL in CI by monkeypatching SpriteList to use SpriteListTextureData:

• test_created_with_capacity with capacities 100, 256, 1000, 1024 and 3000, drawing 600 sprites;
• test_clear_after_growing;
• test_lazy_list_grown_before_first_draw;
• test_storage_is_rows_of_256.

On development, 6 of the 8 fail. Capacities 100 and 256 pass, since they round up to a single 256-wide row either way.

Full suite: 1732 passed. Ruff is clean, and mypy has no new errors. I haven't run it in an actual browser build. A quick check there would be worth doing, but the shader and texture code are the same as the desktop path the tests use.

The changelog has an entry under Unreleased → Fixes.

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