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