vo_opengl: cocoa: output premultiplied alpha

Which is apparently what is expected here. (I'm pretty sure X11
compositors want stright alpha, so 2 code paths are needed.)

3 files changed, 4 insertions, 0 deletions

diff --git a/video/out/opengl/common.h b/video/out/opengl/common.h
index c2eb0e9c2e..b57c698d85 100644
--- a/video/out/opengl/common.h
+++ b/video/out/opengl/common.h
@@ -92,6 +92,7 @@ struct GL {
     int mpgl_caps;              // Bitfield of MPGL_CAP_* constants
     bool debug_context;         // use of e.g. GLX_CONTEXT_DEBUG_BIT_ARB
     int fb_r, fb_g, fb_b;       // frame buffer bit depth (0 if unknown)
+    bool fb_premultiplied;      // assumption about FB alpha compositor usage
 
     void (GLAPIENTRY *Viewport)(GLint, GLint, GLsizei, GLsizei);
     void (GLAPIENTRY *Clear)(GLbitfield);
diff --git a/video/out/opengl/context_cocoa.c b/video/out/opengl/context_cocoa.c
index 1bcfa09755..f2329a29fd 100644
--- a/video/out/opengl/context_cocoa.c
+++ b/video/out/opengl/context_cocoa.c
@@ -129,6 +129,7 @@ static bool create_gl_context(struct MPGLContext *ctx, int vo_flags)
 
     mpgl_load_functions(ctx->gl, (void *)cocoa_glgetaddr, NULL, ctx->vo->log);
     ctx->gl->fb_r = ctx->gl->fb_g = ctx->gl->fb_b = cgl_color_size(ctx);
+    ctx->gl->fb_premultiplied = true;
 
     CGLReleasePixelFormat(p->pix);
 
diff --git a/video/out/opengl/video.c b/video/out/opengl/video.c
index a96a95b5c7..fb7f9ee882 100644
--- a/video/out/opengl/video.c
+++ b/video/out/opengl/video.c
@@ -1527,6 +1527,8 @@ static void pass_convert_yuv(struct gl_video *p)
         GLSL(color.a = 1.0;)
     } else if (p->opts.alpha_mode == 2) { // blend
         GLSL(color = vec4(color.rgb * color.a, 1.0);)
+    } else if (p->gl->fb_premultiplied) {
+        GLSL(color = vec4(color.rgb * color.a, color.a);)
     }
 }