SFML/dotnet/examples/shader/resources/blur.sfx

uniform sampler2D texture;
uniform float offset;

void main()
{
	vec2 offx = vec2(offset, 0.0);
	vec2 offy = vec2(0.0, offset);

	vec4 c0 = texture2D(texture, gl_TexCoord[0].xy);
	vec4 c1 = texture2D(texture, gl_TexCoord[0].xy - offy);
	vec4 c2 = texture2D(texture, gl_TexCoord[0].xy + offy);
	vec4 c3 = texture2D(texture, gl_TexCoord[0].xy - offx);
	vec4 c4 = texture2D(texture, gl_TexCoord[0].xy + offx);

	gl_FragColor =  gl_Color * (c0 * 0.2 + c1 * 0.2 + c2 * 0.2 + c3 * 0.2 + c4 * 0.2);
}