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Avoid making up the format COGL_PIXEL_FORMAT_A_8_PRE

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There are a few places in Cogl that try to set the premult bit on a
pixel format depending on whether it has an alpha channel. However
this breaks if the pixel format is alpha-only because premultiplying
data without any RGB components doesn't make any sense. This adds an
internal macro to check for cases where we should add the premult bit
called COGL_PIXEL_FORMAT_CAN_HAVE_PREMULT. This now gets used in all
places that previously just checking for COGL_A_BIT.

https://bugzilla.gnome.org/show_bug.cgi?id=671016

Reviewed-by: Robert Bragg <robert@linux.intel.com>
This commit is contained in:
Neil Roberts 2012-02-29 12:27:19 +00:00
parent 2b9aca20a8
commit 323adc0c14
5 changed files with 19 additions and 6 deletions
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2
cogl/cogl-bitmap-fallback.c
View File

@ -375,7 +375,7 @@ _cogl_bitmap_fallback_convert (CoglBitmap *src_bmp,
/* Initialize destination bitmap */
dst_rowstride = sizeof(guint8) * dst_bpp * width;
/* Copy the premult bit if the new format has an alpha channel */
if ((dst_format & COGL_A_BIT))
if (COGL_PIXEL_FORMAT_CAN_HAVE_PREMULT (dst_format))
dst_format = ((src_format & COGL_PREMULT_BIT) |
(dst_format & ~COGL_PREMULT_BIT));

4
cogl/cogl-bitmap.c
View File

@ -85,7 +85,8 @@ _cogl_bitmap_convert_premult_status (CoglBitmap *bmp,
{
/* Do we need to unpremultiply? */
if ((bmp->format & COGL_PREMULT_BIT) > 0 &&
(dst_format & COGL_PREMULT_BIT) == 0)
(dst_format & COGL_PREMULT_BIT) == 0 &&
COGL_PIXEL_FORMAT_CAN_HAVE_PREMULT (dst_format))
/* Try unpremultiplying using imaging library */
return (_cogl_bitmap_unpremult (bmp)
/* ... or try fallback */
@ -93,6 +94,7 @@ _cogl_bitmap_convert_premult_status (CoglBitmap *bmp,
/* Do we need to premultiply? */
if ((bmp->format & COGL_PREMULT_BIT) == 0 &&
COGL_PIXEL_FORMAT_CAN_HAVE_PREMULT (bmp->format) &&
(dst_format & COGL_PREMULT_BIT) > 0)
/* Try premultiplying using imaging library */
return (_cogl_bitmap_premult (bmp)

12
cogl/cogl-private.h
View File

@ -102,6 +102,18 @@ _cogl_pixel_format_get_bytes_per_pixel (CoglPixelFormat format);
gboolean
_cogl_pixel_format_is_endian_dependant (CoglPixelFormat format);
/*
* COGL_PIXEL_FORMAT_CAN_HAVE_PREMULT(format):
* @format: a #CoglPixelFormat
*
* Returns TRUE if the pixel format can take a premult bit. This is
* currently true for all formats that have an alpha channel except
* COGL_PIXEL_FORMAT_A_8 (because that doesn't have any other
* components to multiply by the alpha).
*/
#define COGL_PIXEL_FORMAT_CAN_HAVE_PREMULT(format) \
(((format) & COGL_A_BIT) && (format) != COGL_PIXEL_FORMAT_A_8)
G_END_DECLS
#endif /* __COGL_PRIVATE_H__ */

5
cogl/cogl-texture.c
View File

@ -160,8 +160,7 @@ _cogl_texture_determine_internal_format (CoglPixelFormat src_format,
* this. */
if (dst_format == COGL_PIXEL_FORMAT_ANY)
{
if ((src_format & COGL_A_BIT) &&
src_format != COGL_PIXEL_FORMAT_A_8)
if (COGL_PIXEL_FORMAT_CAN_HAVE_PREMULT (src_format))
return src_format | COGL_PREMULT_BIT;
else
return src_format;
@ -1231,7 +1230,7 @@ cogl_texture_get_data (CoglTexture *texture,
/* We can assume that whatever data GL gives us will have the
premult status of the original texture */
if ((closest_format & COGL_A_BIT))
if (COGL_PIXEL_FORMAT_CAN_HAVE_PREMULT (closest_format))
closest_format = ((closest_format & ~COGL_PREMULT_BIT) |
(texture_format & COGL_PREMULT_BIT));

2
cogl/cogl.c
View File

@ -438,7 +438,7 @@ _cogl_read_pixels_with_rowstride (int x,
bpp = _cogl_pixel_format_get_bytes_per_pixel (format);
bmp_format = format;
if ((format & COGL_A_BIT))
if (COGL_PIXEL_FORMAT_CAN_HAVE_PREMULT (format & COGL_A_BIT))
{
/* We match the premultiplied state of the target buffer to the
* premultiplied state of the framebuffer so that it will get