shader_type canvas_item;
render_mode unshaded;

uniform float cutoff: hint_range(0.0, 1.0);
uniform float smooth_size: hint_range(0.0, 0.1);
uniform sampler2D mask: hint_default_black;

void fragment() {
    float value = texture(mask, UV).r;
    float alpha = smoothstep(
        cutoff,
        cutoff + smooth_size,
        value * (1.0 - smooth_size) + smooth_size
    );
    COLOR = vec4(COLOR.rgb, alpha);
}