I have shader code following " vec4 txindex = texelFetch( s_texture, ivec2(int(v_texcoord.x),int(v_texcoord.y)) ,0 );\n" " vec4 txcol = texelFetch( s_color, ivec2( ( int(txindex.g*65280.0) | int(txindex.r*255.0)) ,0 ) , 0 );\n" it seems txindex does not have enough precision, the seccond texelFetch ...