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textoverlay: unpremultiply text image

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The GstVideoOverlayComposition only supports unpremultiplied ARGB
(for now anyway, support for pre-multiplied alpha is planned.)
This commit is contained in:
Thibault Saunier 2011-11-28 10:05:50 -03:00 committed by Tim-Philipp Müller
parent cbcf1e0b46
commit 785e006de9
1 changed files with 24 additions and 3 deletions
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27
ext/pango/gsttextoverlay.c
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@ -1172,10 +1172,11 @@ gst_text_overlay_adjust_values_with_fontdesc (GstTextOverlay * overlay,
}
#define CAIRO_UNPREMULTIPLY(a,r,g,b) G_STMT_START { \
b = (a > 0) ? MIN ((b * 255 + a / 2) / a, 255) : 0; \
g = (a > 0) ? MIN ((g * 255 + a / 2) / a, 255) : 0; \
r = (a > 0) ? MIN ((r * 255 + a / 2) / a, 255) : 0; \
*b = (a > 0) ? MIN ((*b * 255 + a / 2) / a, 255) : 0; \
*g = (a > 0) ? MIN ((*g * 255 + a / 2) / a, 255) : 0; \
*r = (a > 0) ? MIN ((*r * 255 + a / 2) / a, 255) : 0; \
} G_STMT_END
static void
gst_text_overlay_get_pos (GstTextOverlay * overlay, gint * xpos, gint * ypos)
{
@ -1241,6 +1242,23 @@ gst_text_overlay_get_pos (GstTextOverlay * overlay, gint * xpos, gint * ypos)
*ypos += overlay->deltay;
}
static inline void
gst_text_overlay_unpremultiply (GstTextOverlay * overlay)
{
guint i, j;
guint8 *pimage, *text_image = GST_BUFFER_DATA (overlay->text_image);
for (i = 0; i < overlay->image_height; i++) {
pimage = text_image + 4 * (i * overlay->image_width);
for (j = 0; j < overlay->image_width; j++) {
CAIRO_UNPREMULTIPLY (pimage[CAIRO_ARGB_A], &pimage[CAIRO_ARGB_R],
&pimage[CAIRO_ARGB_G], &pimage[CAIRO_ARGB_B]);
pimage += 4;
}
}
}
static inline void
gst_text_overlay_set_composition (GstTextOverlay * overlay)
{
@ -1419,6 +1437,9 @@ gst_text_overlay_render_pangocairo (GstTextOverlay * overlay,
g_mutex_unlock (GST_TEXT_OVERLAY_GET_CLASS (overlay)->pango_lock);
/* As the GstVideoOverlayComposition supports only unpremultiply ARGB,
* we need to unpermultiply it */
gst_text_overlay_unpremultiply (overlay);
gst_text_overlay_set_composition (overlay);
}