SoftCloneFrag.glsl

//
// Copyright (C) 2023  Autodesk, Inc. All Rights Reserved. 
// 
// SPDX-License-Identifier: Apache-2.0 
//
#if __VERSION__ >= 150
out vec4 FragColor; 
#define FRAGCOLOR FragColor
#else
#define FRAGCOLOR gl_FragColor
#define in varying
#endif

#extension GL_ARB_texture_rectangle : require

uniform sampler2DRect texture0; /*texture*/
uniform vec2 cloneOffset;
in vec2 TexCoord0; // paint stroke texcoord [-1, 1]
in vec2 TexCoord1; // paint stroke texcoord w.r.t. frame

void main() 
{
    vec2  m      = TexCoord0 - vec2(0.5, 0.5);
    float mag    = sqrt(m.x * m.x + m.y * m.y);
    float radius = 0.5;
    float bot    = 0.01831563888; /* exp(-4.0) */
    float ratio  = mag * 2.0 / radius;

    if (ratio <= 2.0) FRAGCOLOR.a = exp(-ratio*ratio)-bot*ratio*0.5;
    else FRAGCOLOR.a = 0.0;

    vec2  shifted = TexCoord1 + cloneOffset;
    FRAGCOLOR.rgb = texture2DRect(texture0, shifted).rgb;
}