Use textureOffset() wherever possible to save some tedious arithmetic.

[nageru] / derivatives.frag

diff --git a/derivatives.frag b/derivatives.frag
index f5394c37a3f26031ca54d4244824568ae6477af6..e5e355700f56e1197d1ca3cd2326ae346d98a651 100644 (file)
--- a/derivatives.frag
+++ b/derivatives.frag
@@ -4,19 +4,18 @@ in vec2 tc;
 out vec2 derivatives;
 
 uniform sampler2D tex;
-uniform vec2 inv_image_size;
 
 void main()
 {
-       float x_m2 = texture(tex, vec2(tc.x - 2.0 * inv_image_size.x), tc.y).x;
-       float x_m1 = texture(tex, vec2(tc.x -       inv_image_size.x), tc.y).x;
-       float x_p1 = texture(tex, vec2(tc.x +       inv_image_size.x), tc.y).x;
-       float x_p2 = texture(tex, vec2(tc.x + 2.0 * inv_image_size.x), tc.y).x;
+       float x_m2 = textureOffset(tex, tc, ivec2(-2,  0)).x;
+       float x_m1 = textureOffset(tex, tc, ivec2(-1,  0)).x;
+       float x_p1 = textureOffset(tex, tc, ivec2( 1,  0)).x;
+       float x_p2 = textureOffset(tex, tc, ivec2( 2,  0)).x;
 
-       float y_m2 = texture(tex, vec2(tc.x, tc.y - 2.0 * inv_image_size.y)).x;
-       float y_m1 = texture(tex, vec2(tc.x, tc.y -       inv_image_size.y)).x;
-       float y_p1 = texture(tex, vec2(tc.x, tc.y +       inv_image_size.y)).x;
-       float y_p2 = texture(tex, vec2(tc.x, tc.y + 2.0 * inv_image_size.y)).x;
+       float y_m2 = textureOffset(tex, tc, ivec2( 0, -2)).x;
+       float y_m1 = textureOffset(tex, tc, ivec2( 0, -1)).x;
+       float y_p1 = textureOffset(tex, tc, ivec2( 0,  1)).x;
+       float y_p2 = textureOffset(tex, tc, ivec2( 0,  2)).x;
 
        derivatives.x = (x_p1 - x_m1) * (2.0/3.0) + (x_m2 - x_p2) * (1.0/12.0);
        derivatives.y = (y_p1 - y_m1) * (2.0/3.0) + (y_m2 - y_p2) * (1.0/12.0);