【Godot】オーラエフェクトシェーダー

shader_type canvas_item;
render_mode blend_premul_alpha;

// This shader only works properly with premultiplied alpha blend mode.
// オーラの幅
uniform float aura_width = 4.0;
// オーラの色
uniform vec4 aura_color: hint_color;
// オーラの点滅速度
uniform float aura_blink_interval = 2.0;

void fragment() {
	float w = aura_width  * abs(sin(TIME * aura_blink_interval));
	
	vec4 col = texture(TEXTURE, UV);
	vec2 ps = TEXTURE_PIXEL_SIZE;
	float a;
	float maxa = col.a;
	float mina = col.a;

	a = texture(TEXTURE, UV + vec2(0.0, -w) * ps).a;
	maxa = max(a, maxa);
	mina = min(a, mina);

	a = texture(TEXTURE, UV + vec2(0.0, w) * ps).a;
	maxa = max(a, maxa);
	mina = min(a, mina);

	a = texture(TEXTURE, UV + vec2(-w, 0.0) * ps).a;
	maxa = max(a, maxa);
	mina = min(a, mina);

	a = texture(TEXTURE, UV + vec2(w, 0.0) * ps).a;
	maxa = max(a, maxa);
	mina = min(a, mina);

	col.rgb *= col.a;

	COLOR = col;
	COLOR.rgb += aura_color.rgb * (maxa - mina);
}