Use textureSize() instead of sending in uniforms manually. Same result, less code...

[nageru] / motion_search.vert

diff --git a/motion_search.vert b/motion_search.vert
index d08f499a5dce90213969e9d98bb8013c2416e21e..28b65c225bfafdb2ab0d5f0678175ab978472930 100644 (file)
--- a/motion_search.vert
+++ b/motion_search.vert
@@ -1,15 +1,33 @@
 #version 450 core
 
 in vec2 position;
-in vec2 texcoord;
 out vec2 flow_tc;
-out vec2 patch_bottom_left_texel;  // Center of bottom-left texel of patch.
+out vec2 patch_center;
 
-uniform float inv_flow_width, inv_flow_height;
-uniform float inv_image_width, inv_image_height;
+uniform sampler2D flow_tex;
 
 void main()
 {
+       // Patch placement: We want the outermost patches to have centers exactly in the
+       // image corners, so that the bottom-left patch has centre (0,0) and the
+       // upper-right patch has center (1,1). The position we get in is _almost_ there;
+       // since the quad's corners are in (0,0) and (1,1), the fragment shader will get
+       // centers in x=0.5/w, x=1.5/w and so on (and similar for y).
+       //
+       // In other words, find some f(x) = ax + b so that
+       //
+       //   a 0.5 / w + b = 0
+       //   a (1.0 - 0.5 / w) + b = 1
+       //
+       // which gives
+       //
+       //   a = 1 / (w - 1)
+       //   b = w / 2 (w - 1)
+       vec2 flow_size = textureSize(flow_tex, 0);
+       vec2 a = flow_size / (flow_size - 1);
+       vec2 b = -1.0 / (2 * (flow_size - 1.0));
+       patch_center = a * position + b;
+
        // The result of glOrtho(0.0, 1.0, 0.0, 1.0, 0.0, 1.0) is:
        //
        //   2.000  0.000  0.000 -1.000
@@ -17,8 +35,5 @@ void main()
        //   0.000  0.000 -2.000 -1.000
        //   0.000  0.000  0.000  1.000
        gl_Position = vec4(2.0 * position.x - 1.0, 2.0 * position.y - 1.0, -1.0, 1.0);
-       flow_tc = texcoord;
-
-       vec2 patch_bottom_left = texcoord - vec2(0.5, 0.5) * vec2(inv_flow_width, inv_flow_height);
-       patch_bottom_left_texel = patch_bottom_left + vec2(0.5, 0.5) * vec2(inv_image_width, inv_image_height);
+       flow_tc = position;
 }