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[xlib] Fix _draw_image_surface() with opaque images.

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If the image was opaque with no alpha channel, we filled the output alpha
with 0. Typically, the destination surface for dithering is an RGB window,
so this bug went unnoticed. However, test/xlib-expose-event is an example
where we generate an intermediate alpha-only pixmap for use as a stencil
and this was failing as the mask was left completely transparent. The
simple solution is to ensure that for opaque images, the output alpha is
set to the maximum permissible value.
This commit is contained in:
Chris Wilson 2008-10-30 09:54:47 +00:00
parent c3940d342a
commit 42711a5586
1 changed files with 8 additions and 1 deletions
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9
src/cairo-xlib-surface.c
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@ -1055,7 +1055,14 @@ _draw_image_surface (cairo_xlib_surface_t *surface,
else
in_pixel = row[x];
a = _field_to_8 (in_pixel & image_masks.alpha_mask, i_a_width, i_a_shift);
/* If the incoming image has no alpha channel, then the input
* is opaque and the output should have the maximum alpha value.
* For all other channels, their absence implies 0.
*/
if (image_masks.alpha_mask == 0x0)
a = 0xff;
else
a = _field_to_8 (in_pixel & image_masks.alpha_mask, i_a_width, i_a_shift);
r = _field_to_8 (in_pixel & image_masks.red_mask , i_r_width, i_r_shift);
g = _field_to_8 (in_pixel & image_masks.green_mask, i_g_width, i_g_shift);
b = _field_to_8 (in_pixel & image_masks.blue_mask , i_b_width, i_b_shift);