You might want to try this PostFx-Shader I derived from http://glsl.herokuapp.com/e#14949.0   You might want to play around with some of the values but I think, it's a good start.   Vertex-Shader: #version 400 uniform mat4 projectionmatrix; uniform mat4 drawmatrix; uniform vec2 offset; uniform vec2 position[4]; in vec3 vertex_position; void main(void) { gl_Position = projectionmatrix * (drawmatrix * vec4(position[gl_VertexID]+offset, 0.0, 1.0)); }   Fragment-Shader: #version 40
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