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compositor: Use 255 as maximum alpha instead of 256

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255 will easily become 0 in the blending function as they expect
the maximum value to be 255.

Can be reproduce with

gst-launch-1.0 videotestsrc pattern=ball ! c.sink_0 \
               videotestsrc pattern=snow ! c.sink_1 \
               compositor name=c \
                 sink_0::zorder=0 sink_1::zorder=1 sink_0::crossfade-ratio=0.5 \
                 background=black ! \
               videoconvert ! xvimagesink

crossfade-ratio +/- 0.001 makes it work correctly and the same happens
at e.g. 0.25, 0.75, N*0.0625

https://bugzilla.gnome.org/show_bug.cgi?id=796846
This commit is contained in:
Sebastian Dröge 2018-07-20 16:25:02 +03:00
parent 14ab3972ef
commit b0ae6a5221
1 changed files with 5 additions and 7 deletions
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12
gst/compositor/blend.c
View file

@ -33,8 +33,6 @@
#include <gst/video/video.h>
#define BLEND(D,S,alpha) (((D) * (256 - (alpha)) + (S) * (alpha)) >> 8)
GST_DEBUG_CATEGORY_STATIC (gst_compositor_blend_debug);
#define GST_CAT_DEFAULT gst_compositor_blend_debug
@ -61,7 +59,7 @@ method##_ ##name (GstVideoFrame * srcframe, gint xpos, gint ypos, \
dest_width = GST_VIDEO_FRAME_COMP_WIDTH (destframe, 0); \
dest_height = GST_VIDEO_FRAME_COMP_HEIGHT (destframe, 0); \
\
s_alpha = CLAMP ((gint) (src_alpha * 256), 0, 256); \
s_alpha = CLAMP ((gint) (src_alpha * 255), 0, 255); \
\
/* If it's completely transparent... we just return */ \
if (G_UNLIKELY (s_alpha == 0)) \
@ -247,7 +245,7 @@ _blend_##format_name (const guint8 * src, guint8 * dest, \
return; \
} \
\
b_alpha = CLAMP ((gint) (src_alpha * 256), 0, 256); \
b_alpha = CLAMP ((gint) (src_alpha * 255), 0, 255); \
\
BLENDLOOP(dest, dest_stride, src, src_stride, b_alpha, src_width, src_height);\
} \
@ -492,7 +490,7 @@ _blend_##format_name (const guint8 * src, guint8 * dest, \
return; \
} \
\
b_alpha = CLAMP ((gint) (src_alpha * 256), 0, 256); \
b_alpha = CLAMP ((gint) (src_alpha * 255), 0, 255); \
\
BLENDLOOP(dest, dest_stride, src, src_stride, b_alpha, src_width, src_height); \
} \
@ -691,7 +689,7 @@ blend_##name (GstVideoFrame * srcframe, gint xpos, gint ypos, \
src_stride = GST_VIDEO_FRAME_COMP_STRIDE (srcframe, 0); \
dest_stride = GST_VIDEO_FRAME_COMP_STRIDE (destframe, 0); \
\
b_alpha = CLAMP ((gint) (src_alpha * 256), 0, 256); \
b_alpha = CLAMP ((gint) (src_alpha * 255), 0, 255); \
\
/* adjust src pointers for negative sizes */ \
if (xpos < 0) { \
@ -857,7 +855,7 @@ blend_##name (GstVideoFrame * srcframe, gint xpos, gint ypos, \
src_stride = GST_VIDEO_FRAME_COMP_STRIDE (srcframe, 0); \
dest_stride = GST_VIDEO_FRAME_COMP_STRIDE (destframe, 0); \
\
b_alpha = CLAMP ((gint) (src_alpha * 256), 0, 256); \
b_alpha = CLAMP ((gint) (src_alpha * 255), 0, 255); \
\
xpos = GST_ROUND_UP_2 (xpos); \
\