Do alpha blending maybe right.

diff --git a/src/lib/ffmpeg_decoder.cc b/src/lib/ffmpeg_decoder.cc
index 5167ce4886a1c4a93c53cc69cae7df50a2db7660..8feb366239cbb0b19e04a63552aff60ec989af50 100644 (file)
--- a/src/lib/ffmpeg_decoder.cc
+++ b/src/lib/ffmpeg_decoder.cc
@@ -275,26 +275,24 @@ FFmpegDecoder::do_pass ()
                                                for (int sub_x = 0; sub_x < rect->w; ++sub_x) {
 
                                                        uint32_t const val = palette[*sub_line_p++];
-                                                       int const   red = (val &       0xff);
-                                                       int const green = (val &     0xff00) >> 8;
-                                                       int const  blue = (val &   0xff0000) >> 16;
-                                                       int const alpha = (val & 0xff000000) >> 24;
+                                                       
+                                                       int const     red =  (val &       0xff);
+                                                       int const   green =  (val &     0xff00) >> 8;
+                                                       int const    blue =  (val &   0xff0000) >> 16;
+                                                       float const alpha = ((val & 0xff000000) >> 24) / 255.0;
 
-                                                       if (alpha) {
-                                                               *frame_line_y_p = RGB_TO_Y_CCIR (red, green, blue);
-                                                       }
-                                                       frame_line_y_p++;
+                                                       int const cy = *frame_line_y_p;
+
+                                                       *frame_line_y_p++ = int (cy * (1 - alpha)) + int (RGB_TO_Y_CCIR (red, green, blue) * alpha);
                                                        
                                                        current_u |= ((RGB_TO_U_CCIR (red, green, blue, 0) & 0xf0) >> 4) << (4 * subsample_step);
                                                        current_v |= ((RGB_TO_V_CCIR (red, green, blue, 0) & 0xf0) >> 4) << (4 * subsample_step);
 
                                                        if (subsample_step == 1 && (sub_y % 2) == 0) {
-                                                               if (alpha) {
-                                                                       *frame_line_u_p = current_u;
-                                                                       *frame_line_v_p = current_v;
-                                                               }
-                                                               frame_line_u_p++;
-                                                               frame_line_v_p++;
+                                                               int const cu = *frame_line_u_p;
+                                                               int const cv = *frame_line_v_p;
+                                                               *frame_line_u_p++ = int (cu * (1 - alpha)) + int (current_u * alpha);
+                                                               *frame_line_v_p++ = int (cv * (1 - alpha)) + int (current_v * alpha);
                                                                current_u = current_v = 0;
                                                        }