toon4.fsh

precision mediump float;

uniform sampler2D input_texture;
uniform float coefficient;

varying vec2 texture_coordinate;
varying vec2 left_texture_coordinate;
varying vec2 right_texture_coordinate;

varying vec2 top_texture_coordinate;
varying vec2 top_left_texture_coordinate;
varying vec2 top_right_texture_coordinate;

varying vec2 bottom_texture_coordinate;
varying vec2 bottom_left_texture_coordinate;
varying vec2 bottom_right_texture_coordinate;

float grad()
{
    vec3 left           = texture2D(input_texture, left_texture_coordinate).rgb;
	vec3 right          = texture2D(input_texture, right_texture_coordinate).rgb;
    vec3 top            = texture2D(input_texture, top_texture_coordinate).rgb;
	vec3 top_left       = texture2D(input_texture, top_left_texture_coordinate).rgb;
	vec3 top_right      = texture2D(input_texture, top_right_texture_coordinate).rgb;
	vec3 bottom         = texture2D(input_texture, bottom_texture_coordinate).rgb;
	vec3 bottom_left    = texture2D(input_texture, bottom_left_texture_coordinate).rgb;
	vec3 bottom_right   = texture2D(input_texture, bottom_right_texture_coordinate).rgb;
    
    vec3 grayscale = vec3(0.3, 0.59, 0.11);
    
    left           = vec3(dot(grayscale, left));
    right          = vec3(dot(grayscale, right));
    top            = vec3(dot(grayscale, top));
    top_left       = vec3(dot(grayscale, top_left));
    top_right      = vec3(dot(grayscale, top_right));
    bottom         = vec3(dot(grayscale, bottom));
    bottom_left    = vec3(dot(grayscale, bottom_left));
    bottom_right   = vec3(dot(grayscale, bottom_right));
	
	float dX = -top_left.r - 2.0*left.r - bottom_left.r + top_right.r + 2.0*right.r + bottom_right.r;
	float dY = -top_left.r - 2.0*top.r - top_right.r + bottom_left.r + 2.0*bottom.r + bottom_right.r;
    
    float mag = length(vec2(dX, dY));
    float thresholdTest = 1.0 - step(coefficient, mag);
    return thresholdTest;
}

void main()
{
    float gradient = grad();
    gl_FragColor = vec4(texture2D(input_texture, texture_coordinate).bgr * gradient, 1.0);    
}