- char buf[256];
- sprintf(buf, "const vec3 PREFIX(offset) = vec3(%.8f, %.8f, %.8f);\n",
- offset[0], offset[1], offset[2]);
- frag_shader += buf;
-
- sprintf(buf, "const vec3 PREFIX(scale) = vec3(%.8f, %.8f, %.8f);\n",
- scale[0], scale[1], scale[2]);
- frag_shader += buf;
-
- // OpenGL has texel center in (0.5, 0.5), but different formats have
- // chroma in various other places. If luma samples are X, the chroma
- // sample is *, and subsampling is 3x3, the situation with chroma
- // center in (0.5, 0.5) looks approximately like this:
- //
- // X X
- // *
- // X X
- //
- // If, on the other hand, chroma center is in (0.0, 0.5) (common
- // for e.g. MPEG-4), the figure changes to:
- //
- // X X
- // *
- // X X
- //
- // Obviously, the chroma plane here needs to be moved to the left,
- // which means _adding_ 0.5 to the texture coordinates when sampling
- // chroma.
- float chroma_offset_x = (0.5f - ycbcr_format.chroma_x_position) / widths[1];
- float chroma_offset_y = (0.5f - ycbcr_format.chroma_y_position) / heights[1];
- sprintf(buf, "const vec2 PREFIX(chroma_offset) = vec2(%.8f, %.8f);\n",
- chroma_offset_x, chroma_offset_y);
- frag_shader += buf;
+ float cb_offset_x = compute_chroma_offset(
+ ycbcr_format.cb_x_position, ycbcr_format.chroma_subsampling_x, widths[1]);
+ float cb_offset_y = compute_chroma_offset(
+ ycbcr_format.cb_y_position, ycbcr_format.chroma_subsampling_y, heights[1]);
+ frag_shader += output_glsl_vec2("PREFIX(cb_offset)", cb_offset_x, cb_offset_y);
+
+ float cr_offset_x = compute_chroma_offset(
+ ycbcr_format.cr_x_position, ycbcr_format.chroma_subsampling_x, widths[2]);
+ float cr_offset_y = compute_chroma_offset(
+ ycbcr_format.cr_y_position, ycbcr_format.chroma_subsampling_y, heights[2]);
+ frag_shader += output_glsl_vec2("PREFIX(cr_offset)", cr_offset_x, cr_offset_y);