// const int OUTPUT_RES = 700;
// const float RES = float( OUTPUT_RES - 1 );


uniform sampler2D LeftUnit, RightUnit;
// uniform float T;
// uniform float ResS, ResT;
// varying float	X, Y;

void main()
{
	vec2 st = gl_TexCoord[0].st;
	// int row = int( RES*(X+1.)/2. + 0.5 );
	// int col = int( RES*(Y+1.)/2. + 0.5 );
	int row = int( gl_FragCoord.x );
	int col = int( gl_FragCoord.y );
	int sum = row + col;

	vec4 color;
	if( ( sum % 2 ) == 0 )
	{
		color = texture2D( LeftUnit,  st );
	}
	else
	{
		color = texture2D( RightUnit, st );
	}

	gl_FragColor = vec4( color.rgb, 1. );
}