add a simple but nice example of convolution filters in glsl

shows basics of image processing with glsl

progs/glsl/convolution.frag

@@ -0,0 +1,21 @@
+
+const int KernelSize = 9;
+
+//texture offsets
+uniform vec2 Offset[KernelSize];
+//convolution kernel
+uniform vec4 KernelValue[KernelSize];
+uniform sampler2D srcTex;
+uniform vec4 ScaleFactor;
+uniform vec4 BaseColor;
+
+void main(void)
+{
+    int i;
+    vec4 sum = vec4(0.0);
+    for (i = 0; i < KernelSize; ++i) {
+        vec4 tmp = texture2D(srcTex, gl_TexCoord[0].st + Offset[i]);
+        sum += tmp * KernelValue[i];
+    }
+    gl_FragColor = sum * ScaleFactor + BaseColor;
+}