//
// Fragment shader for Gaussian splats.
// Renders a Gaussian splat within a quad, discarding fragments outside the unit circle.
// Applies an approximate Gaussian falloff based on distance from the center and outputs
// a color modulated by the alpha and Gaussian weight.
//
void main() {
    if (v_splitDirection < 0.0 && gl_FragCoord.x > czm_splitPosition) discard;
    if (v_splitDirection > 0.0 && gl_FragCoord.x < czm_splitPosition) discard;

    float A = -dot(v_vertPos, v_vertPos);
    if (A < -4.) {
        discard;
    }

    float B = exp(A * 4.) * v_splatColor.a ;
    out_FragColor = vec4(v_splatColor.rgb * B , B);
}