#version 330 compatibility in vec4 inVar; out vec4 outVar; varying vec4 varyingVar; void main() { gl_FragColor = varyingVar; // link ERROR: user output was used gl_FragData[1] = inVar; // link ERROR: user output was used int buffer = 4; } #extension GL_ARB_separate_shader_objects : enable in gl_PerFragment { vec4 gl_Color; }; void foo() { vec4 c = gl_Color; outVar = inVar; } in gl_block { // ERROR int gl_i; } gl_name; in myBlock { int gl_i; // ERROR } gl_name; // ERROR in gl_PerVertex { // ERROR vec4 gl_FragCoord; } gl_in[]; in gl_PerVertex { // ERROR vec4 gl_FragCoord; }; // ERROR