init commit, with sample code

SFML/examples/shader/resources/blur.frag

@@ -0,0 +1,20 @@
+uniform sampler2D texture;
+uniform float blur_radius;
+
+void main()
+{
+    vec2 offx = vec2(blur_radius, 0.0);
+    vec2 offy = vec2(0.0, blur_radius);
+
+    vec4 pixel = texture2D(texture, gl_TexCoord[0].xy)               * 4.0 +
+                 texture2D(texture, gl_TexCoord[0].xy - offx)        * 2.0 +
+                 texture2D(texture, gl_TexCoord[0].xy + offx)        * 2.0 +
+                 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;
+
+    gl_FragColor =  gl_Color * (pixel / 16.0);
+}