[anthonytheinventor]

Problem

Every ClutterShaderEffect that sets its own shader source leaks its offscreen texture when it is destroyed: one stage-sized texture, about 4 MB at 1366x768. Extensions that add these effects to windows leak GPU memory on every window open and close. With BlurCinnamon's window blur, Cinnamon's GPU memory grew by about 175 MB over 3 open/close cycles.

Cause

In cogl/cogl/deprecated/cogl-shader.c, _cogl_shader_compile_real() keeps a reference to the pipeline the shader was compiled for (shader->compilation_pipeline), only to compare its layer numbers on the next compile. That pipeline owns the user program, and the user program owns the shader, so the reference makes a cycle:

pipeline → user program → shader → compilation_pipeline (the same pipeline)

None of them is ever freed, and neither is the effect's texture held by the pipeline's layer. Separately, _cogl_shader_free() never frees the shader source string.

Fix

Store the pipeline's layer indices instead of a reference to the pipeline. The check only needs the layer indices and texture units, and texture units follow layer order, so the indices cover both. The shader frees the indices and its source string when it is freed.

Testing

On Linux Mint 22.3 with Muffin 6.6.3 (Intel HD 4000, X11). This file is the same on master, and the patch builds there without warnings.

• 20 ClutterShaderEffects with their own shader source, created and destroyed: GPU memory +100 MB before, 0 after.
• BlurCinnamon 2.6.1 with window blur, opening and closing a blurred window: +175 MB over 3 cycles before, 0 over 10 cycles after.
• Rendered output is pixel-identical before and after.
• Cogl test suite: 52/52 pass.
• A temporary test reusing one shader across pipelines with different layers (not included) gives identical results before and after. It reaches both the reuse and recompile paths. Valgrind reports no errors in this code.

I worked on this with Claude Code and tested it on my machine.