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<html><head></head><body><div style="font-size: 12pt; font-family: Calibri,sans-serif;"><div>Is this patch not preventing unrolling? If so, performance will be rather badly affected? (Yes, obviously this depends on the compiler)</div><div><br></div><div>-- </div><div>Rémi Denis-Courmont</div><div>Sent from my NVIDIA Tegra-powered device</div><br><div id="htc_header">----- Reply message -----<br>De : "Martin Storsjö" <martin@martin.st><br>Pour : <vlc-devel@videolan.org><br>Objet : [vlc-devel] [PATCH] blend: Handle alpha when blending in RGBA buffers<br>Date : jeu., janv. 16, 2014 21:31</div></div><br><pre style="word-wrap: break-word; white-space: pre-wrap;">Previously the alpha channel wasn't set at all, and the RGB
components were blended without regard to the existing alpha
value.
---
modules/video_filter/blend.cpp | 26 +++++++++++++++++++++++---
1 file changed, 23 insertions(+), 3 deletions(-)
diff --git a/modules/video_filter/blend.cpp b/modules/video_filter/blend.cpp
index 1f403fe..6552899 100644
--- a/modules/video_filter/blend.cpp
+++ b/modules/video_filter/blend.cpp
@@ -297,9 +297,29 @@ public:
void merge(unsigned dx, const CPixel &spx, unsigned a, bool)
{
uint8_t *dst = getPointer(dx);
- ::merge(&dst[offset_r], spx.i, a);
- ::merge(&dst[offset_g], spx.j, a);
- ::merge(&dst[offset_b], spx.k, a);
+ if (has_alpha) {
+ // Handle different cases of existing alpha in the
+ // destination buffer. If the existing alpha is 0,
+ // the RGB components should be copied as is and
+ // alpha set to 'a'. If the existing alpha is 255,
+ // this should behave just as the non-alpha case below.
+
+ // First blend the existing color based on its
+ // alpha with the incoming color.
+ ::merge(&dst[offset_r], spx.i, 255 - dst[offset_a]);
+ ::merge(&dst[offset_g], spx.j, 255 - dst[offset_a]);
+ ::merge(&dst[offset_b], spx.k, 255 - dst[offset_a]);
+ // Now blend in the new color on top with the normal formulas.
+ ::merge(&dst[offset_r], spx.i, a);
+ ::merge(&dst[offset_g], spx.j, a);
+ ::merge(&dst[offset_b], spx.k, a);
+ // Finally set dst_a = (255 * src_a + prev_a * (255 - src_a))/255.
+ ::merge(&dst[offset_a], 255, a);
+ } else {
+ ::merge(&dst[offset_r], spx.i, a);
+ ::merge(&dst[offset_g], spx.j, a);
+ ::merge(&dst[offset_b], spx.k, a);
+ }
}
void nextLine()
{
--
1.7.9.4
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