varying vec2 v_vTexcoord;
varying vec4 v_vColour;

uniform vec2  dimension;
uniform float height;
uniform float smooth;

float bright(in vec4 col) { return dot(col.rgb, vec3(0.2126, 0.7152, 0.0722)) * col.a; }

void main() {
	vec2 tx = 1. / dimension;
    
	vec4 c    = texture2D(gm_BaseTexture, v_vTexcoord);
	float siz = 1. + smooth;
	
    float col = bright(c);
    float h0  = bright(texture2D(gm_BaseTexture, v_vTexcoord + tx * vec2(-1.,  0.) * siz));
    float h1  = bright(texture2D(gm_BaseTexture, v_vTexcoord + tx * vec2( 1.,  0.) * siz));
    float v0  = bright(texture2D(gm_BaseTexture, v_vTexcoord + tx * vec2( 0., -1.) * siz));
    float v1  = bright(texture2D(gm_BaseTexture, v_vTexcoord + tx * vec2( 0.,  1.) * siz));
    
	vec2 normal;
	
	if(smooth > 0.) {
		float d0  = bright(texture2D(gm_BaseTexture, v_vTexcoord + tx * vec2( 1., -1.) * siz));
	    float d1  = bright(texture2D(gm_BaseTexture, v_vTexcoord + tx * vec2(-1., -1.) * siz));
	    float d2  = bright(texture2D(gm_BaseTexture, v_vTexcoord + tx * vec2(-1.,  1.) * siz));
	    float d3  = bright(texture2D(gm_BaseTexture, v_vTexcoord + tx * vec2( 1.,  1.) * siz));
    
	   	normal =     (vec2(h1 - col, 0.)
					+ vec2(col - h0, 0.)
					+ vec2(0., v1 - col)
					+ vec2(0., col - v0)
					+ vec2(d0 - col, col - d0) / sqrt(2.)
					+ vec2(col - d1, col - d1) / sqrt(2.)
					+ vec2(col - d2, d2 - col) / sqrt(2.)
					+ vec2(d3 - col, d3 - col) / sqrt(2.)
				 ) / (2. + 2. * sqrt(2.));
				 
	} else {
		normal =     (vec2(h1 - col, 0.)
					+ vec2(col - h0, 0.)
					+ vec2(0., v1 - col)
					+ vec2(0., col - v0)
				 ) / 2.;
	}
	
	normal = normal * height + 0.5;
	
    gl_FragColor = vec4(normal, 1., c.a);
}