Magnifying glass shader

magnifier.shadertoy

// (c) 2011 detunized (http://detunized.net)
// Paste the shader below into http://shadertoy.com
// Click and drag the mouse around

#ifdef GL_ES
precision highp float;
#endif

uniform vec2 resolution;
uniform sampler2D tex0;

void mainImage(out vec4 fragColor, in vec2 fragCoord )
{
	float R = 100.0;
	float h = 20.0;
	float hr = R * sqrt(1.0 - ((R - h) / R) * ((R - h) / R));

	vec2 xy = gl_FragCoord.xy - iMouse.xy;
    
    float x = xy.x;
    float y = xy.y;
    
	float r = sqrt(x * x + y * y);
    
    vec2 new_xy = xy;
    
    if (r < hr)
    {
        new_xy = xy * (R - h) / sqrt(R*R - r*r);
    }

	
	
	fragColor = texture(iChannel0, (new_xy + iMouse.xy) / iResolution.xy);
}