uniform sampler2D ImageUnit;
uniform float T;
uniform float ResS, ResT;

uniform float MagTol;
uniform float Quantize;

void main()
{
	vec2 st = gl_TexCoord[0].st;
	vec3 rgb = texture2D( ImageUnit,  st ).rgb;

	vec4 color = vec4( 1., 0., 0., 1. );

	vec2 stp0 = vec2(1./ResS,  0. );
	vec2 st0p = vec2(0.     ,  1./ResT);
	vec2 stpp = vec2(1./ResS,  1./ResT);
	vec2 stpm = vec2(1./ResS, -1./ResT);
	float i00 =   dot( texture2D( ImageUnit, st ).rgb, vec3(0.2125,0.7154,0.0721) );
	float im1m1 = dot( texture2D( ImageUnit, st-stpp ).rgb, vec3(0.2125,0.7154,0.0721) );
	float ip1p1 = dot( texture2D( ImageUnit, st+stpp ).rgb, vec3(0.2125,0.7154,0.0721) );
	float im1p1 = dot( texture2D( ImageUnit, st-stpm ).rgb, vec3(0.2125,0.7154,0.0721) );
	float ip1m1 = dot( texture2D( ImageUnit, st+stpm ).rgb, vec3(0.2125,0.7154,0.0721) );
	float im10 =  dot( texture2D( ImageUnit, st-stp0 ).rgb, vec3(0.2125,0.7154,0.0721) );
	float ip10 =  dot( texture2D( ImageUnit, st+stp0 ).rgb, vec3(0.2125,0.7154,0.0721) );
	float i0m1 =  dot( texture2D( ImageUnit, st-st0p ).rgb, vec3(0.2125,0.7154,0.0721) );
	float i0p1 =  dot( texture2D( ImageUnit, st+st0p ).rgb, vec3(0.2125,0.7154,0.0721) );
	float h = -1.*im1p1 - 2.*i0p1 - 1.*ip1p1  +  1.*im1m1 + 2.*i0m1 + 1.*ip1m1;
	float v = -1.*im1m1 - 2.*im10 - 1.*im1p1  +  1.*ip1m1 + 2.*ip10 + 1.*ip1p1;
	

	float mag = sqrt( h*h + v*v );
	if( mag > MagTol )
	{
		color = vec4( 0., 0., 0., 1. );
	}
	else
	{
		rgb.rgb *= Quantize;
		rgb.rgb += vec3( .5, .5, .5 );
		ivec3 irgb = ivec3( rgb.rgb );
		rgb.rgb = vec3( irgb ) / Quantize;
		color = vec4( rgb, 1. );
	}

	gl_FragColor = color;
}