shader-1.frag

vec4 stroke(float distance, float linewidth, float antialias, vec4 stroke)
{
	float t = linewidth / 2.0 - antialias;
	float signed_distance = distance;
	float border_distance = abs(signed_distance) - t;
	float alpha = border_distance / antialias;
	alpha = exp(-alpha * alpha);
	
    if( border_distance < 0.0 )
		return stroke;
	else
		return vec4(stroke.rgb, stroke.a * alpha);
}


float eq_test_1(vec2 u, vec2 center, float radius)
{
    vec2 v = u - center;
    
	return abs(sqrt(v.x * v.x + v.y * v.y * abs(v.y + v.x * v.x) / 20.0) - radius);
}

float eq_circle(vec2 u, vec2 center, float radius)
{
    vec2 v = u - center;
    
	return abs(sqrt(v.x * v.x + v.y * v.y) - radius);
}

float eq_line(vec2 u, float a, float b, float c)
{
	return a * u.x + b * u.y + c;
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    //vec4 col = stroke(eq_line(fragCoord, 0.5, -1.0, 0.25),
    //                  2.0, 1.0, vec4(0.5, 0.5, 0.5, 1.0));
    
    vec4 col = stroke(eq_test_1(fragCoord, vec2(100.0, 100.0), 50.0), 2.0, 1.0, vec4(0.5, 0.5, 0.5, 1.0));
    
    fragColor = vec4(1.0) * (1.0 - col.a) + col * col.a;
}