// DIRECTION_VERTICAL will be #defined to 1 if we are scaling vertically, // and 0 otherwise. uniform sampler2D PREFIX(sample_tex); uniform int PREFIX(num_samples); uniform float PREFIX(num_loops); uniform float PREFIX(sample_x_scale); uniform float PREFIX(sample_x_offset); uniform float PREFIX(slice_height); // We put the fractional part of the offset (-0.5 to 0.5 pixels) in the weights // because we have to (otherwise they'd do nothing). However, the support texture // has limited numerical precision; we'd need as much of it as we can for // getting the subpixel sampling right, and adding a large constant to each value // will reduce the precision further. Thus, the non-fractional part of the offset // is sent in through a uniform that we simply add in. (It should be said that // for high values of (dst_size/num_loop), we're pretty much hosed anyway wrt. // this accuracy.) // // Unfortunately, we cannot just do it at the beginning of the shader, // since the texcoord value is used to index into the support texture, // and if zoom != 1, the support texture will not wrap properly, causing // us to read the wrong texels. (Also remember that whole_pixel_offset is // measured in _input_ pixels and tc is in _output_ pixels, although we could // compensate for that.) However, the shader should be mostly bandwidth bound // and not ALU bound, so an extra add per sample shouldn't be too hopeless. uniform float PREFIX(whole_pixel_offset); // Sample a single weight. First fetch information about where to sample // and the weight from sample_tex, and then read the pixel itself. vec4 PREFIX(do_sample)(vec2 tc, int i) { vec2 sample_tc; sample_tc.x = float(i) * PREFIX(sample_x_scale) + PREFIX(sample_x_offset); #if DIRECTION_VERTICAL sample_tc.y = tc.y * PREFIX(num_loops); #else sample_tc.y = tc.x * PREFIX(num_loops); #endif vec2 sample = tex2D(PREFIX(sample_tex), sample_tc).rg; #if DIRECTION_VERTICAL tc.y = sample.g + floor(sample_tc.y) * PREFIX(slice_height) + PREFIX(whole_pixel_offset); #else tc.x = sample.g + floor(sample_tc.y) * PREFIX(slice_height) + PREFIX(whole_pixel_offset); #endif return vec4(sample.r) * INPUT(tc); } vec4 FUNCNAME(vec2 tc) { vec4 sum = PREFIX(do_sample)(tc, 0); for (int i = 1; i < PREFIX(num_samples); ++i) { sum += PREFIX(do_sample)(tc, i); } return sum; } #undef DIRECTION_VERTICAL