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

[nageru] / sobel.frag

diff --git a/sobel.frag b/sobel.frag
index c4dabd519712465a9d2a5495617ac9c1e2708c5b..518b6f8abcdadb4491b8e1187f6cea3e696fa477 100644 (file)
--- a/sobel.frag
+++ b/sobel.frag
@@ -26,24 +26,16 @@ void main()
        // Computing both directions at once allows us to get away with eight
        // texture samples instead of twelve.
 
-       float x_left   = tc.x - inv_image_size.x;
-       float x_mid    = tc.x; 
-       float x_right  = tc.x + inv_image_size.x;
-
-       float y_top    = tc.y + inv_image_size.y;  // Note the bottom-left coordinate system.
-       float y_mid    = tc.y;
-       float y_bottom = tc.y - inv_image_size.y;
- 
-       float top_left     = texture(tex, vec2(x_left,  y_top)).x;
-       float left         = texture(tex, vec2(x_left,  y_mid)).x;
-       float bottom_left  = texture(tex, vec2(x_left,  y_bottom)).x;
-
-       float top          = texture(tex, vec2(x_mid,   y_top)).x;
-       float bottom       = texture(tex, vec2(x_mid,   y_bottom)).x;
-
-       float top_right    = texture(tex, vec2(x_right, y_top)).x;
-       float right        = texture(tex, vec2(x_right, y_mid)).x;
-       float bottom_right = texture(tex, vec2(x_right, y_bottom)).x;
+       float top_left     = textureOffset(tex, tc, ivec2(-1,  1)).x;  // Note the bottom-left coordinate system.
+       float left         = textureOffset(tex, tc, ivec2(-1,  0)).x;
+       float bottom_left  = textureOffset(tex, tc, ivec2(-1, -1)).x;
+
+       float top          = textureOffset(tex, tc, ivec2( 0,  1)).x;
+       float bottom       = textureOffset(tex, tc, ivec2( 0, -1)).x;
+
+       float top_right    = textureOffset(tex, tc, ivec2( 1,  1)).x;
+       float right        = textureOffset(tex, tc, ivec2( 1,  0)).x;
+       float bottom_right = textureOffset(tex, tc, ivec2( 1, -1)).x;
 
        gradients.x = (top_right + 2.0f * right + bottom_right) - (top_left + 2.0f * left + bottom_left);
        gradients.y = (top_left + 2.0 * top + top_right) - (bottom_left + 2.0f * bottom + bottom_right);