uniform sampler2D m_ColorMap;
uniform vec2      m_OverlayOrigin;
uniform vec2      m_OverlaySize;
uniform float     m_FadePx;

in  vec2 texCoord;
out vec4 outFragColor;

void main() {
    vec4 col = texture(m_ColorMap, texCoord);

    // Abstand des Fragments vom nächsten Overlay-Rand in Screen-Pixeln
    float distL = gl_FragCoord.x - m_OverlayOrigin.x;
    float distR = (m_OverlayOrigin.x + m_OverlaySize.x) - gl_FragCoord.x;
    float distB = gl_FragCoord.y - m_OverlayOrigin.y;
    float distT = (m_OverlayOrigin.y + m_OverlaySize.y) - gl_FragCoord.y;
    float edgeFade = clamp(min(min(distL, distR), min(distB, distT)) / m_FadePx, 0.0, 1.0);

    outFragColor = vec4(col.rgb, col.a * edgeFade);
}