#version 100
#extension GL_OES_standard_derivatives : enable

#ifdef GL_ES
precision mediump float;
#endif

varying vec2 fragTexCoord;
varying vec4 fragColor;

uniform sampler2D texture0;
uniform vec4 colDiffuse;
uniform float pxRange;

float median(float r, float g, float b) {
	return max(min(r, g), min(max(r, g), b));
}

float screenPxRange(vec2 uv) {
	vec2 duv_dx = dFdx(uv);
	vec2 duv_dy = dFdy(uv);
	float scale = 0.5 * (length(duv_dx) + length(duv_dy));
	return max(scale * pxRange, 1.0);
}

void main() {
	vec3 msd = texture2D(texture0, fragTexCoord).rgb;
	float sd = median(msd.r, msd.g, msd.b);
	float spx = screenPxRange(fragTexCoord);
	float dist = spx * (sd - 0.5);
	float opacity = clamp(dist + 0.5, 0.0, 1.0);

	gl_FragColor = vec4(fragColor.rgb, fragColor.a * opacity) * colDiffuse;
}