funny-animated-gif-from-profile-picture-bot/shaders/fragment.glsl

/*
    Copyright (C) 2021  hiimgoodpack

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/
#version 330 core

in vec2 vFragCoord;

uniform float aHorizontalOffset;
uniform sampler2D aTexture;

void main() {
	float distanceFromCenterSquared = dot(vFragCoord, vFragCoord);

	// alpha = 0 if fragment is outside circle
	// alpha = 1 if fragment is inside circle
	float alpha = distanceFromCenterSquared > 1 ? 0 : 1;

	// An equation which seems to work
	float specular = distanceFromCenterSquared * (-0.5f*vFragCoord.x + vFragCoord.y) + 1;

	vec2 texCoord = vFragCoord * vec2(0.5,0.5) + vec2(0.5+aHorizontalOffset,0.5);

	gl_FragColor = vec4(texture(aTexture, texCoord).xyz*specular, alpha);
}