Re: [FFmpeg-devel] [PATCH] avfilter/vf_overlay: fix alpha blending for planar formats with a transparent background

[Marton Balint]

On Mon, 7 Aug 2017, Marton Balint wrote:



On Sat, 5 Aug 2017, Michael Niedermayer wrote:


On Fri, Aug 04, 2017 at 10:23:55AM +0200, Marton Balint wrote:

When the background had an alpha channel, the old code in blend_plane
calculated premultiplied alpha from the destination plane colors instead 

of the

destination alpha.

Also the calculation of the output alpha should only happen after the 

color

planes are already finished.

Fixes output of:
ffplay -f lavfi "testsrc2=alpha=32[a];color=black[b];[b][a]overlay[out0]"


if it is easy, please add a fate test when / after you push this



Ok, will do as a second step. I am going to apply this soon.


Applied.

Regards,
Marton
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Re: [FFmpeg-devel] [PATCH] avfilter/vf_overlay: fix alpha blending for planar formats with a transparent background

[Marton Balint]

On Sat, 5 Aug 2017, Michael Niedermayer wrote:


On Fri, Aug 04, 2017 at 10:23:55AM +0200, Marton Balint wrote:

When the background had an alpha channel, the old code in blend_plane
calculated premultiplied alpha from the destination plane colors instead of the
destination alpha.

Also the calculation of the output alpha should only happen after the color
planes are already finished.

Fixes output of:
ffplay -f lavfi "testsrc2=alpha=32[a];color=black[b];[b][a]overlay[out0]"


if it is easy, please add a fate test when / after you push this



Ok, will do as a second step. I am going to apply this soon.

Regards,
Marton
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Re: [FFmpeg-devel] [PATCH] avfilter/vf_overlay: fix alpha blending for planar formats with a transparent background

[Michael Niedermayer]

On Fri, Aug 04, 2017 at 10:23:55AM +0200, Marton Balint wrote:
> When the background had an alpha channel, the old code in blend_plane
> calculated premultiplied alpha from the destination plane colors instead of 
> the
> destination alpha.
> 
> Also the calculation of the output alpha should only happen after the color
> planes are already finished.
> 
> Fixes output of:
> ffplay -f lavfi "testsrc2=alpha=32[a];color=black[b];[b][a]overlay[out0]"

if it is easy, please add a fate test when / after you push this

thx

[...]
-- 
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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-- Epicurus


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[FFmpeg-devel] [PATCH] avfilter/vf_overlay: fix alpha blending for planar formats with a transparent background

[Marton Balint]

When the background had an alpha channel, the old code in blend_plane
calculated premultiplied alpha from the destination plane colors instead of the
destination alpha.

Also the calculation of the output alpha should only happen after the color
planes are already finished.

Fixes output of:
ffplay -f lavfi "testsrc2=alpha=32[a];color=black[b];[b][a]overlay[out0]"

Signed-off-by: Marton Balint 
---
 libavfilter/vf_overlay.c | 28 
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/libavfilter/vf_overlay.c b/libavfilter/vf_overlay.c
index ad292a61c1..52f09fae1f 100644
--- a/libavfilter/vf_overlay.c
+++ b/libavfilter/vf_overlay.c
@@ -508,7 +508,7 @@ static av_always_inline void blend_plane(AVFilterContext 
*ctx,
 int dst_hp = AV_CEIL_RSHIFT(dst_h, vsub);
 int yp = y>>vsub;
 int xp = x>>hsub;
-uint8_t *s, *sp, *d, *dp, *a, *ap;
+uint8_t *s, *sp, *d, *dp, *dap, *a, *da, *ap;
 int jmax, j, k, kmax;
 
 j = FFMAX(-yp, 0);
@@ -517,12 +517,14 @@ static av_always_inline void blend_plane(AVFilterContext 
*ctx,
   + (yp+j)* dst->linesize[dst_plane]
   + dst_offset;
 ap = src->data[3] + (j<linesize[3];
+dap = dst->data[3] + ((yp+j) << vsub) * dst->linesize[3];
 
 for (jmax = FFMIN(-yp + dst_hp, src_hp); j < jmax; j++) {
 k = FFMAX(-xp, 0);
 d = dp + (xp+k) * dst_step;
 s = sp + k;
 a = ap + (k<linesize[3]] +
-   d[1] + d[src->linesize[3]+1]) >> 2;
+alpha_d = (da[0] + da[dst->linesize[3]] +
+   da[1] + da[dst->linesize[3]+1]) >> 2;
 } else if (hsub || vsub) {
 alpha_h = hsub && k+1 < src_wp ?
-(d[0] + d[1]) >> 1 : d[0];
+(da[0] + da[1]) >> 1 : da[0];
 alpha_v = vsub && j+1 < src_hp ?
-(d[0] + d[src->linesize[3]]) >> 1 : d[0];
+(da[0] + da[dst->linesize[3]]) >> 1 : da[0];
 alpha_d = (alpha_v + alpha_h) >> 1;
 } else
-alpha_d = d[0];
+alpha_d = da[0];
 alpha = UNPREMULTIPLY_ALPHA(alpha, alpha_d);
 }
 *d = FAST_DIV255(*d * (255 - alpha) + *s * alpha);
 s++;
 d += dst_step;
+da += 1 << hsub;
 a += 1 << hsub;
 }
 dp += dst->linesize[dst_plane];
 sp += src->linesize[i];
 ap += (1 << vsub) * src->linesize[3];
+dap += (1 << vsub) * dst->linesize[3];
 }
 }
 
@@ -622,15 +626,15 @@ static av_always_inline void 
blend_image_yuv(AVFilterContext *ctx,
 const int dst_w = dst->width;
 const int dst_h = dst->height;
 
-if (main_has_alpha)
-alpha_composite(src, dst, src_w, src_h, dst_w, dst_h, x, y);
-
 blend_plane(ctx, dst, src, src_w, src_h, dst_w, dst_h, 0, 0,   0, x, 
y, main_has_alpha,
 s->main_desc->comp[0].plane, s->main_desc->comp[0].offset, 
s->main_desc->comp[0].step);
 blend_plane(ctx, dst, src, src_w, src_h, dst_w, dst_h, 1, hsub, vsub, x, 
y, main_has_alpha,
 s->main_desc->comp[1].plane, s->main_desc->comp[1].offset, 
s->main_desc->comp[1].step);
 blend_plane(ctx, dst, src, src_w, src_h, dst_w, dst_h, 2, hsub, vsub, x, 
y, main_has_alpha,
 s->main_desc->comp[2].plane, s->main_desc->comp[2].offset, 
s->main_desc->comp[2].step);
+
+if (main_has_alpha)
+alpha_composite(src, dst, src_w, src_h, dst_w, dst_h, x, y);
 }
 
 static av_always_inline void blend_image_planar_rgb(AVFilterContext *ctx,
@@ -645,15 +649,15 @@ static av_always_inline void 
blend_image_planar_rgb(AVFilterContext *ctx,
 const int dst_w = dst->width;
 const int dst_h = dst->height;
 
-if (main_has_alpha)
-alpha_composite(src, dst, src_w, src_h, dst_w, dst_h, x, y);
-
 blend_plane(ctx, dst, src, src_w, src_h, dst_w, dst_h, 0, 0,   0, x, 
y, main_has_alpha,
 s->main_desc->comp[1].plane, s->main_desc->comp[1].offset, 
s->main_desc->comp[1].step);
 blend_plane(ctx, dst, src, src_w, src_h, dst_w, dst_h, 1, hsub, vsub, x, 
y, main_has_alpha,
 s->main_desc->comp[2].plane, s->main_desc->comp[2].offset, 
s->main_desc->comp[2].step);
 blend_plane(ctx, dst, src, src_w, src_h, dst_w, dst_h, 2, hsub, vsub, x, 
y, main_has_alpha,