// https://github.com/aras-p/glsl-optimizer/issues/48 attribute vec3 _in_position; uniform mat4 mtx; void main() { mat4 m = mtx; // chained assignments used to not work, #48 m[0][1] = m[0][2] = m[0][3] = 0.0; gl_Position = m * vec4(_in_position,1); }