Add support for offsets in ResampleEffect.

[movit] / resample_effect.frag

diff --git a/resample_effect.frag b/resample_effect.frag
index 6aac29d72674cc93ce6f605c14c9a59d518d6182..bce33ce369c769bd29b797def82d0e00a15b969a 100644 (file)
--- a/resample_effect.frag
+++ b/resample_effect.frag
@@ -3,8 +3,18 @@
 
 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 and 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 the beginning of the shader.
+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.
@@ -13,21 +23,26 @@ 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;
+       sample_tc.y = tc.y * PREFIX(num_loops);
 #else
-       sample_tc.y = tc.x;
+       sample_tc.y = tc.x * PREFIX(num_loops);
 #endif
-       vec2 sample = texture2D(PREFIX(sample_tex), sample_tc).rg;
+       vec2 sample = tex2D(PREFIX(sample_tex), sample_tc).rg;
 
 #if DIRECTION_VERTICAL
-       tc.y = sample.g;
+       tc.y = sample.g + floor(sample_tc.y) * PREFIX(slice_height);
 #else
-       tc.x = sample.g;
+       tc.x = sample.g + floor(sample_tc.y) * PREFIX(slice_height);
 #endif
        return vec4(sample.r) * INPUT(tc);
 }
 
 vec4 FUNCNAME(vec2 tc) {
+#if DIRECTION_VERTICAL
+       tc.y += PREFIX(whole_pixel_offset);
+#else
+       tc.x += PREFIX(whole_pixel_offset);
+#endif
        vec4 sum = PREFIX(do_sample)(tc, 0);
        for (int i = 1; i < PREFIX(num_samples); ++i) {
                sum += PREFIX(do_sample)(tc, i);