shader_type canvas_item;

// Parameters
uniform float alpha_threshold : hint_range(0.0, 1.0) = 0.1; // below this = fully transparent
uniform float alpha_modifier : hint_range(0.0, 1.0) = 1.0;  // global alpha multiplier

void fragment() {
    // Sample the current frame automatically
    vec4 tex_color = texture(TEXTURE, UV);

    // Convert color to luminance (grayscale)
    float lum = dot(tex_color.rgb, vec3(0.299, 0.587, 0.114));

    // Apply threshold: if below threshold, alpha = 0
    float alpha = lum < alpha_threshold ? 0.0 : lum;

    // Apply global modifier
    alpha *= alpha_modifier;

    COLOR = vec4(tex_color.rgb, alpha);
}