CATransform3D:透视变换后计算高度

Question

我有一个高度为50的图层,我将它围绕x轴旋转...如何在旋转进行时计算高度？

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

绕 y 轴旋转

• y' = y*cos q - z*sin q
• z' = y*sin q + z*cos q
• x' = x

高度为 y1 - y0。因此计算新的 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;