share/shaders/circles.fs


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#version 330

// Input vertex attributes (from vertex shader)
in vec2 fragTexCoord;
in vec4 fragColor;

// Output fragment color
out vec4 finalColor;

void main()
{
    float radius = 0.1;
    vec2 distance_from_center = fragTexCoord - vec2(0.5);
// s <= 0 -> inside circle
// s > 0  -> outside circle
    if (length(distance_from_center) <= 0.5) {
        float s = length(distance_from_center) - radius;
        if (s <= 0) {
            finalColor = fragColor*1.5;
        } else {
            float t = 1 - s / (0.5 - radius);
            finalColor = vec4(fragColor.xyz, t*t);
        }
    } else {
        finalColor = vec4(0);
    }
}