glcolorconvert: fix planar YUV download

- sample the u and v planes properly
- output the correctly scaled u and v planes for different chroma block sizes

gst-libs/gst/gl/gstglcolorconvert.c

@@ -237,15 +237,39 @@ static const gchar frag_RGB_to_PLANAR_YUV[] =
     "#endif\n"
     "varying vec2 v_texcoord;\n"
     "uniform sampler2D tex;\n"
-    "uniform float w, h;\n"
+    "uniform float width;\n"
+    "uniform float height;\n"
+    "uniform vec2 chroma_sampling;\n"
     RGB_TO_YUV_COEFFICIENTS
     "void main(void) {\n"
     "  float y, u, v;\n"
+    "  vec4 uv_texel;\n"
     "  vec4 texel = texture2D(tex, v_texcoord).%c%c%c%c;\n"
-    "  vec4 texel2 = texture2D(tex, v_texcoord * 2.0).%c%c%c%c;\n"
+    /* One u and v sample can be generated by a nxm sized block given by
+     * @chroma_sampling.  The result is the average of all the values in the
+     * block computed with a rolling average.
+     */
+    "  vec2 size = vec2(width, height);\n"
+    "  vec2 pos = v_texcoord * size;\n"
+       /* scale for chroma size */
+    "  vec2 chroma_pos = v_texcoord * chroma_sampling * size;\n"
+       /* offset chroma to the center of the first texel in the block */
+    "  chroma_pos -= clamp(chroma_sampling * 0.5 - 0.5, vec2(0.0), chroma_sampling);\n"
+    "  if (chroma_pos.x < width && chroma_pos.y < height) {\n"
+    "    for (int i = 0; i < int(chroma_sampling.x); i++) {\n"
+    "      vec2 delta = vec2 (float(i), 0.0);\n"
+    "      for (int j = 0; j < int(chroma_sampling.y); j++) {\n"
+    "        int n = (i+1)*(j+1);\n"
+    "        delta.y = float(j);\n"
+    "        vec4 sample = texture2D(tex, (chroma_pos + delta) / size).%c%c%c%c;\n"
+             /* rolling average */
+    "        uv_texel = (float(n-1) * uv_texel + sample) / float(n);\n"
+    "      }\n"
+    "    }\n"
+    "  }\n"
     "  y = dot(texel.rgb, coeff1);\n"
-    "  u = dot(texel2.rgb, coeff2);\n"
+    "  u = dot(uv_texel.rgb, coeff2);\n"
-    "  v = dot(texel2.rgb, coeff3);\n"
+    "  v = dot(uv_texel.rgb, coeff3);\n"
     "  y += offset.x;\n"
     "  u += offset.y;\n"
     "  v += offset.z;\n"
@@ -380,6 +404,7 @@ struct ConvertInfo
   gfloat *cms_coeff1;           /* r,y */
   gfloat *cms_coeff2;           /* g,u */
   gfloat *cms_coeff3;           /* b,v */
+  gfloat chroma_sampling[2];
 };
 
 struct _GstGLColorConvertPrivate
@@ -418,6 +443,8 @@ static void
 gst_gl_color_convert_init (GstGLColorConvert * convert)
 {
   convert->priv = GST_GL_COLOR_CONVERT_GET_PRIVATE (convert);
+
+  gst_gl_color_convert_reset (convert);
 }
 
 /**
@@ -477,6 +504,9 @@ gst_gl_color_convert_reset (GstGLColorConvert * convert)
     convert->priv->out_tex[i] = NULL;
   }
 
+  convert->priv->convert_info.chroma_sampling[0] = 1.0f;
+  convert->priv->convert_info.chroma_sampling[1] = 1.0f;
+
   if (convert->shader) {
     gst_object_unref (convert->shader);
     convert->shader = NULL;
@@ -810,6 +840,7 @@ _RGB_to_YUV (GstGLColorConvert * convert)
   struct ConvertInfo *info = &convert->priv->convert_info;
   GstVideoFormat in_format = GST_VIDEO_INFO_FORMAT (&convert->in_info);
   const gchar *in_format_str = gst_video_format_to_string (in_format);
+  GstVideoFormat out_format = GST_VIDEO_INFO_FORMAT (&convert->out_info);
   gchar *pixel_order = _RGB_pixel_order (in_format_str, "rgba");
   const gchar *alpha;
 
@@ -818,7 +849,7 @@ _RGB_to_YUV (GstGLColorConvert * convert)
 
   info->shader_tex_names[0] = "tex";
 
-  switch (GST_VIDEO_INFO_FORMAT (&convert->out_info)) {
+  switch (out_format) {
     case GST_VIDEO_FORMAT_AYUV:
       alpha = _is_RGBx (in_format) ? "1.0" : "texel.a";
       info->frag_prog = g_strdup_printf (frag_RGB_to_AYUV, pixel_order[0],
@@ -834,6 +865,17 @@ _RGB_to_YUV (GstGLColorConvert * convert)
           pixel_order[0], pixel_order[1], pixel_order[2], pixel_order[3],
           pixel_order[0], pixel_order[1], pixel_order[2], pixel_order[3]);
       info->out_n_textures = 3;
+      if (out_format == GST_VIDEO_FORMAT_Y444) {
+        info->chroma_sampling[0] = info->chroma_sampling[1] = 1.0f;
+      } else if (out_format == GST_VIDEO_FORMAT_Y42B) {
+        info->chroma_sampling[0] = 2.0f;
+        info->chroma_sampling[1] = 1.0f;
+      } else if (out_format == GST_VIDEO_FORMAT_Y41B) {
+        info->chroma_sampling[0] = 4.0f;
+        info->chroma_sampling[1] = 1.0f;
+      } else {
+        info->chroma_sampling[0] = info->chroma_sampling[1] = 2.0f;
+      }
       break;
     case GST_VIDEO_FORMAT_YUY2:
       info->frag_prog = g_strdup_printf (frag_RGB_to_YUY2_UYVY,
@@ -1053,6 +1095,13 @@ _init_convert (GstGLColorConvert * convert)
 
   gst_gl_shader_set_uniform_1f (convert->shader, "width",
       GST_VIDEO_INFO_WIDTH (&convert->in_info));
+  gst_gl_shader_set_uniform_1f (convert->shader, "height",
+      GST_VIDEO_INFO_HEIGHT (&convert->in_info));
+
+  if (info->chroma_sampling[0] > 0.0f && info->chroma_sampling[1] > 0.0f) {
+    gst_gl_shader_set_uniform_2fv (convert->shader, "chroma_sampling", 1,
+        info->chroma_sampling);
+  }
 
   gst_gl_context_clear_shader (convert->context);