[require] GLSL >= 1.20 [vertex shader] void main() { gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex; } [fragment shader] void main() { const vec3 v = log(vec3(1.0, 0.1353352832366127, 54.598150033144236)); if (v == vec3(0.0, -2.0, 4.0)) gl_FragColor = vec4(0.0, 1.0, 0.0, 1.0); else gl_FragColor = vec4(0.0, 1.0, 0.0, 1.0); } [test] draw rect -1 -1 2 2 probe all rgb 0 1 0