imported shader example

resources/edge.frag

@@ -0,0 +1,32 @@
+uniform sampler2D texture;
+uniform float edge_threshold;
+
+void main()
+{
+    const float offset = 1.0 / 512.0;
+    vec2 offx = vec2(offset, 0.0);
+    vec2 offy = vec2(0.0, offset);
+
+    vec4 hEdge = texture2D(texture, gl_TexCoord[0].xy - offy)        * -2.0 +
+                 texture2D(texture, gl_TexCoord[0].xy + offy)        *  2.0 +
+                 texture2D(texture, gl_TexCoord[0].xy - offx - offy) * -1.0 +
+                 texture2D(texture, gl_TexCoord[0].xy - offx + offy) *  1.0 +
+                 texture2D(texture, gl_TexCoord[0].xy + offx - offy) * -1.0 +
+                 texture2D(texture, gl_TexCoord[0].xy + offx + offy) *  1.0;
+
+    vec4 vEdge = texture2D(texture, gl_TexCoord[0].xy - offx)        *  2.0 +
+                 texture2D(texture, gl_TexCoord[0].xy + offx)        * -2.0 +
+                 texture2D(texture, gl_TexCoord[0].xy - offx - offy) *  1.0 +
+                 texture2D(texture, gl_TexCoord[0].xy - offx + offy) * -1.0 +
+                 texture2D(texture, gl_TexCoord[0].xy + offx - offy) *  1.0 +
+                 texture2D(texture, gl_TexCoord[0].xy + offx + offy) * -1.0;
+
+    vec3 result = sqrt(hEdge.rgb * hEdge.rgb + vEdge.rgb * vEdge.rgb);
+    float edge = length(result);
+    vec4 pixel = gl_Color * texture2D(texture, gl_TexCoord[0].xy);
+    if (edge > (edge_threshold * 8.0))
+        pixel.rgb = vec3(0.0, 0.0, 0.0);
+    else
+        pixel.a = edge_threshold;
+    gl_FragColor = pixel;
+}