816dcfb148
We didn't use pixman for rendering in kmscon. This documents shows some code how we could do it but also explains why this would not improve performance. Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
48 lines
1.8 KiB
Plaintext
48 lines
1.8 KiB
Plaintext
= Pixman accelerated Rendering =
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Several people recommended using pixman for 2D blitting to improve performance
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as pixman has assembler-accelerated backends. However, pixman does not provide
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the functions we need.
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Most rendering operations we need, do alpha compositing with a foreground and
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background color. With pixman we would have to do something like:
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pixman_image_t *pdst = pixman_image_create_bits(
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PIXMAN_x8r8g8b8,
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width,
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height,
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(uint32_t*)dst,
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rb->stride);
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pixman_image_t *pmsk = pixman_image_create_bits(
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PIXMAN_a8,
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width,
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height,
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(uint32_t*)src,
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req->buf->stride);
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pixman_color_t fcol = { 0xffff, 0xffff, 0xffff, 0xffff };
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pixman_image_t *psrc = pixman_image_create_solid_fill(
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&fcol);
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uint32_t bcol = (req->br << 16) | (req->bg << 8) | req->bb;
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pixman_fill((void*)dst, rb->stride / 4, 32, 0, 0,
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width, height, bcol);
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pixman_image_composite(PIXMAN_OP_OVER,
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psrc, pmsk, pdst,
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0, 0, 0, 0, 0, 0,
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width, height);
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That is, we create pixman-images for the destination and the mask. We could
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save them in the video-display and glyph objects so there is actually no need
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to allocate them dynamically. However, the solid color object can be any RGB
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value and thus it must be allocated for every blit. This is way too heavy and
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pixman should really provide a way to create solid images easier. Preferably
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without any function call.
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But the bigger problem is actually that we have to copy data twice. We need to
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first call pixman_fill() and then pixman_image_composite() to get the
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behavior we want. This totally kills performance.
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Profiling pixman_image_composite(), we see that it definitely is better than
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our unoptimized blitters, but we need to add a function which does both
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operations at once to pixman to get a decent performance.
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