perf: replace per-pixel GdkPixbuf allocation with direct Cairo buffer#688
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killerdevildog wants to merge 1 commit intomaoschanz:masterfrom
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perf: replace per-pixel GdkPixbuf allocation with direct Cairo buffer#688killerdevildog wants to merge 1 commit intomaoschanz:masterfrom
killerdevildog wants to merge 1 commit intomaoschanz:masterfrom
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… reads Replace Gdk.pixbuf_get_from_surface() single-pixel calls with direct reads from the Cairo surface buffer via surface.get_data(). This avoids allocating a temporary GdkPixbuf for every pixel read. - Add _read_pixel_rgba() helper that reads BGRA from Cairo ARGB32 buffer, handles alpha un-premultiplication, and returns RGBA bytes - Update utilities_get_rgba_for_xy() to use the new direct read path - Cache buffer data once in utilities_get_magic_path() instead of re-acquiring it per pixel in the ~50K-iteration boundary loop - Fix off-by-one in bounds check (> to >=) Measured ~4.5-5x speedup for pixel reads (3.5 us -> 0.78 us per read).
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benchmarks.patch
perf: Replace per-pixel GdkPixbuf allocation with direct Cairo buffer reads
What
utilities_get_rgba_for_xy()reads a single pixel's color from a Cairo surface. It's used by the paint bucket, color picker, and eraser tools. The paint bucket'sutilities_get_magic_path()calls it up to 50,000 times per fill operation.The old implementation called
Gdk.pixbuf_get_from_surface(surface, x, y, 1, 1)— which allocates a full GdkPixbuf GObject on the heap just to read one pixel. That allocation overhead dominated the cost.What changed
Replaced the GdkPixbuf allocation with a direct read from the Cairo surface's pixel buffer via
surface.get_data(). A new_read_pixel_rgba()helper handles the BGRA→RGBA byte reorder and alpha un-premultiplication that GdkPixbuf was doing internally.In
utilities_get_magic_path(), the surface buffer is now cached once at function entry instead of being re-acquired on every iteration of the hot loop.Also fixed an off-by-one in the bounds check (
x > width→x >= width).Benchmark results
Measured with a microbenchmark on Python 3.12.3 / Cairo 1.18.0 / GTK 3 / Linux:
No behavioral changes — same visual output, same color values returned.