// fog.shader 构造 fog 效果
// noise 为配置好的噪音取样纹理
// texture 为蒙版 mask，用于控制雾气浓度
shader_type canvas_item;
uniform sampler2D noise: repeat_enable;

void fragment() {
	float fog_alpha_1 = texture(noise, vec2(UV.x / 2.0 + TIME /100.0, UV.y / 4.0 - TIME / 100.0)).r;
	float fog_alpha_2 = texture(noise, vec2(UV.x / 2.0 + 0.5 + TIME /50.0, UV.y / 4.0 + 0.5 - TIME / 160.0)).r;
	float fog_alpha_3 = texture(noise, vec2(UV.x / 2.0 + 0.25 + TIME /25.0, UV.y / 4.0 - 0.25 - TIME / 160.0)).r;
	float fog_alpha = mix(fog_alpha_3, mix(fog_alpha_1, fog_alpha_2, 0.5), 0.7);
	// COLOR.a 越接近 1.0， factor 越接近 1.0；COLOR.a 越接近 0.0, factor 越接近 0.0
	float factor = pow(COLOR.a, 2);
	float strength = smoothstep(.0, .2, COLOR.a);
	// factor 越靠近 1， fog_alpha 也靠近 1； factor 越靠近 0.，fog_alpha 越靠近自己
	//COLOR.a = mix(fog_alpha, 1., factor);
	COLOR.a = mix(fog_alpha, 1., factor) * strength;
}