uniform float uTwist;  // 扭曲强度
uniform float uTime;
varying vec2 vUv;

void main() {
    vec2 center = vec2(0.5);
    vec2 offset = vUv - center;
    float radius = length(offset);
    float angle = atan(offset.y, offset.x);

    // 扭曲强度随半径衰减
    float twistAmount = uTwist * (1.0 - radius);

    // 角度添加扭曲偏移
    angle += twistAmount + uTime * 0.5;

    // 转回笛卡尔坐标
    vec2 twistedUv = center + vec2(cos(angle), sin(angle)) * radius;

    // 使用扭曲后的UV采样纹理
    vec4 color = texture2D(uTexture, twistedUv);

    gl_FragColor = color;
}

float ripple(vec2 uv, vec2 center, float time) {
    float dist = length(uv - center);
    float ripple = sin(dist * 20.0 - time * 5.0);
    ripple *= exp(-dist * 3.0); // 衰减

    return ripple * 0.05;
}

void main() {
    vec2 uv = vUv;
    float rippleEffect = ripple(uv, vec2(0.5), uTime);

    // 扭曲方向从中心向外
    vec2 dir = normalize(uv - vec2(0.5));
    vec2 twistedUv = uv + dir * rippleEffect;

    vec4 color = texture2D(uTexture, twistedUv);

    gl_FragColor = color;
}

vec2 vortex(vec2 uv, vec2 center, float radius, float strength) {
    vec2 offset = uv - center;
    float dist = length(offset);

    if (dist < radius) {
        float percent = (radius - dist) / radius;
        float theta = percent * percent * strength * 8.0;
        float sinTheta = sin(theta);
        float cosTheta = cos(theta);

        offset = vec2(
            offset.x * cosTheta - offset.y * sinTheta,
            offset.x * sinTheta + offset.y * cosTheta
        );
    }

    return center + offset;
}