片元旋转UV函数

[taontech]

需要Atan2方法,但是shader没有原生atan2.

float ATan2(vec2 dir)
{
    float angle = asin(dir.x) > 0.0 ? acos(dir.y) : -acos(dir.y);
    return angle;
}
vec2 rotatePt(in vec2 pt, in vec2 center, in float rad){
    float r = length(pt-center);
    float nextRad = ATan2((pt-center)/r);
    nextRad -= rad;
    return vec2(center.x + cos(nextRad)*r, center.y + sin(nextRad)*r);
}