OF_GLSL_SHADER_HEADER precision mediump float; uniform sampler2DRect tex0; in vec2 varyingtexcoord; out vec4 fragColor; void main() { vec4 texColor = texture(tex0, varyingtexcoord); float gray = dot(texColor.rgb, vec3(0.299, 0.587, 0.114)); // Standard luminance formula fragColor = vec4(vec3(gray), 1.0); }