From 44c62a685222f2b018a480246c2946d3e3e7529c Mon Sep 17 00:00:00 2001
From: wm4 <wm4@nowhere>
Date: Fri, 5 Oct 2012 20:37:16 +0200
Subject: sub: switch to premultiplied alpha

Fixes problems with ugly borders.

Note that at least in the DVD sub case, we could have just set all
transparent pixels to black to solve this.

vo_direct3d.c change untested, because mingw is a miserable pile of
crap.
---
 sub/img_convert.c | 24 ++++++++++++++++++++----
 sub/sub.h         |  2 +-
 2 files changed, 21 insertions(+), 5 deletions(-)

(limited to 'sub')

diff --git a/sub/img_convert.c b/sub/img_convert.c
index b8a769f052..888380cf70 100644
--- a/sub/img_convert.c
+++ b/sub/img_convert.c
@@ -166,6 +166,21 @@ bool osd_conv_ass_to_old_p(struct osd_conv_cache *c, struct sub_bitmaps *imgs)
     return true;
 }
 
+static void rgba_to_premultiplied_rgba(uint32_t *colors, size_t count)
+{
+    for (int n = 0; n < count; n++) {
+        uint32_t c = colors[n];
+        int b = c & 0xFF;
+        int g = (c >> 8) & 0xFF;
+        int r = (c >> 16) & 0xFF;
+        int a = (c >> 24) & 0xFF;
+        b = b * a / 255;
+        g = g * a / 255;
+        r = r * a / 255;
+        colors[n] = b | (g << 8) | (r << 16) | (a << 24);
+    }
+}
+
 bool osd_conv_idx_to_rgba(struct osd_conv_cache *c, struct sub_bitmaps *imgs)
 {
     struct sub_bitmaps src = *imgs;
@@ -179,18 +194,19 @@ bool osd_conv_idx_to_rgba(struct osd_conv_cache *c, struct sub_bitmaps *imgs)
     for (int n = 0; n < src.num_parts; n++) {
         struct sub_bitmap *d = &imgs->parts[n];
         struct sub_bitmap *s = &src.parts[n];
-        struct osd_bmp_indexed *sb = s->bitmap;
+        struct osd_bmp_indexed sb = *(struct osd_bmp_indexed *)s->bitmap;
+
+        rgba_to_premultiplied_rgba(sb.palette, 256);
 
         *d = *s;
         d->stride = s->w * 4;
         d->bitmap = talloc_size(c->parts, s->h * d->stride);
 
-        uint32_t *palette = sb->palette;
         uint32_t *outbmp = d->bitmap;
         for (int y = 0; y < s->h; y++) {
-            uint8_t *inbmp = sb->bitmap + y * s->stride;
+            uint8_t *inbmp = sb.bitmap + y * s->stride;
             for (int x = 0; x < s->w; x++)
-                *outbmp++ = palette[*inbmp++];
+                *outbmp++ = sb.palette[*inbmp++];
         }
     }
     return true;
diff --git a/sub/sub.h b/sub/sub.h
index 8649018029..649f196414 100644
--- a/sub/sub.h
+++ b/sub/sub.h
@@ -30,7 +30,7 @@ struct sub_render_params;
 enum sub_bitmap_format {
     SUBBITMAP_EMPTY = 0,// no bitmaps; always has num_parts==0
     SUBBITMAP_LIBASS,   // A8, with a per-surface blend color (libass.color)
-    SUBBITMAP_RGBA,     // B8G8R8A8 (MSB=A, LSB=B), can be scaled
+    SUBBITMAP_RGBA,     // B8G8R8A8 (MSB=A, LSB=B), scaled, premultiplied alpha
     SUBBITMAP_INDEXED,  // scaled, bitmap points to osd_bmp_indexed
     SUBBITMAP_OLD_PLANAR, // like previous, but bitmap points to old_osd_planar
 
-- 
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