CATransform3D：透視變換後計算高度

Question

我有一個高度爲50的圖層，並且我將它圍繞x軸旋轉。 。 。如何在旋轉過程中計算高度？

CATransform3D subLayerTransform = CATransform3DMakeTranslation(0, 0, 0); 
subLayerTransform.m34 = -1/1800; //How does height relate to perspective and angle? 
subLayerTransform = CATransform3DTranslate(subLayerTransform, 0, 0, 0); 
subLayerTransform = CATransform3DRotate(subLayerTransform, 45 * (M_PI/180), 1, 0, 0); 
_transitionLayer.sublayerTransform = subLayerTransform; 

Answer 1

繞y軸

• Y '= Y * COS q - Z *罪q
• Z'= Y *罪Q + Z * COS q
• x'= x

並且高度是y1-y0。爲此計算新的y1和y0：

CGFloat y0 = 0; 
CGFloat y1 = 50; 
CGFloat z = -1800; //This relates to the m34 perspective matrix. 

y0 = y0 * cos(radians(45)) - z * sin(radians(45)); 
y1 = y1 * cos(radians(45)) - z * sin(radians(45)); 

CGFloat newHeight = y1 - y0;