player/js/utils/webgl/shaders/tint_shader.frag

precision mediump float;
uniform sampler2D u_image;
varying vec2 v_texCoord;
uniform float color_amount;
uniform vec4 whiteToColor;
uniform vec4 blackToColor;

void main() {
    vec4 textureValue = texture2D(u_image, v_texCoord);
    float saturation = (textureValue.r + textureValue.g + textureValue.b) / 3.0;
    vec4 textureMapped = blackToColor + (whiteToColor - blackToColor) * saturation;
    gl_FragColor = vec4(mix(textureValue.rgb, textureMapped.rgb, color_amount),textureValue.a);
}