Hi, in case someone is looking for a blur shader for GEM, I put one online at http://www.parasitaere-kapazitaeten.net/Pd/blur_shader. I haven't found a way to pass a matrix to the glsl_program, so the matrix has to be rendered every frame which is a challenge the GPU... If someone has a hint, how to deal with that in a more efficient way, please let me know. the shader is similar to what pix_convolve does, and uses a linear fade. marius.