demotool/shaders/copy.glsl

#version 450 core

layout( location = 0 ) uniform sampler2D u_InputTexture;
layout( location = 1 ) uniform int u_LOD;

layout( location = 0 ) out vec4 color;

void main( void )
{
#if 1
	vec2 ts = textureSize( u_InputTexture , u_LOD );
	vec2 tmp = gl_FragCoord.xy / vec2( 1280. , 720. );
	ivec2 pos = ivec2( ts * tmp );
	color = texelFetch( u_InputTexture , pos , u_LOD );
#else
	vec2 tmp = gl_FragCoord.xy / vec2( 1280. , 720. );
	color = textureLod( u_InputTexture , tmp , float( u_LOD ) );
#endif
}