使用CATransform3D将矩形图像转换为四边形
我有一个图像和一组四点（描述四边形Q）。 我想转换这个图像，以便它符合四边形Q.Photoshop将这个转换称为“扭曲”。 但根据这个四边形的来源（图像在空间移动的视angular），它实际上是一个尺度，旋转和透视matrix的组合。
我想知道是否可以使用CATransform3D 4x4matrix。 你有什么提示如何做到这一点？ 我已经尝试了四个点，并build立了16个方程（A'= A xu中的），但是它不起作用：我不确定我应该用什么作为z，z'，w和w'系数。
下图显示了我想要做的事情：
这里有几点的例子：
276.523, 236.438, 517.656, 208.945, 275.984, 331.285, 502.23, 292.344 261.441, 235.059, 515.09, 211.5, 263.555, 327.066, 500.734, 295 229.031, 161.277, 427.125, 192.562, 229.16, 226, 416.48, 256 我已经在iOS上创build了一个工具包： https ： //github.com/hfossli/AGGeometryKit/
确保你的定位点是左上angular（ CGPointZero ）。
+ (CATransform3D)rectToQuad:(CGRect)rect quadTL:(CGPoint)topLeft quadTR:(CGPoint)topRight quadBL:(CGPoint)bottomLeft quadBR:(CGPoint)bottomRight { return [self rectToQuad:rect quadTLX:topLeft.x quadTLY:topLeft.y quadTRX:topRight.x quadTRY:topRight.y quadBLX:bottomLeft.x quadBLY:bottomLeft.y quadBRX:bottomRight.x quadBRY:bottomRight.y]; } + (CATransform3D)rectToQuad:(CGRect)rect quadTLX:(CGFloat)x1a quadTLY:(CGFloat)y1a quadTRX:(CGFloat)x2a quadTRY:(CGFloat)y2a quadBLX:(CGFloat)x3a quadBLY:(CGFloat)y3a quadBRX:(CGFloat)x4a quadBRY:(CGFloat)y4a { CGFloat X = rect.origin.x; CGFloat Y = rect.origin.y; CGFloat W = rect.size.width; CGFloat H = rect.size.height; CGFloat y21 = y2a - y1a; CGFloat y32 = y3a - y2a; CGFloat y43 = y4a - y3a; CGFloat y14 = y1a - y4a; CGFloat y31 = y3a - y1a; CGFloat y42 = y4a - y2a; CGFloat a = -H*(x2a*x3a*y14 + x2a*x4a*y31 - x1a*x4a*y32 + x1a*x3a*y42); CGFloat b = W*(x2a*x3a*y14 + x3a*x4a*y21 + x1a*x4a*y32 + x1a*x2a*y43); CGFloat c = H*X*(x2a*x3a*y14 + x2a*x4a*y31 - x1a*x4a*y32 + x1a*x3a*y42) - H*W*x1a*(x4a*y32 - x3a*y42 + x2a*y43) - W*Y*(x2a*x3a*y14 + x3a*x4a*y21 + x1a*x4a*y32 + x1a*x2a*y43); CGFloat d = H*(-x4a*y21*y3a + x2a*y1a*y43 - x1a*y2a*y43 - x3a*y1a*y4a + x3a*y2a*y4a); CGFloat e = W*(x4a*y2a*y31 - x3a*y1a*y42 - x2a*y31*y4a + x1a*y3a*y42); CGFloat f = -(W*(x4a*(Y*y2a*y31 + H*y1a*y32) - x3a*(H + Y)*y1a*y42 + H*x2a*y1a*y43 + x2a*Y*(y1a - y3a)*y4a + x1a*Y*y3a*(-y2a + y4a)) - H*X*(x4a*y21*y3a - x2a*y1a*y43 + x3a*(y1a - y2a)*y4a + x1a*y2a*(-y3a + y4a))); CGFloat g = H*(x3a*y21 - x4a*y21 + (-x1a + x2a)*y43); CGFloat h = W*(-x2a*y31 + x4a*y31 + (x1a - x3a)*y42); CGFloat i = W*Y*(x2a*y31 - x4a*y31 - x1a*y42 + x3a*y42) + H*(X*(-(x3a*y21) + x4a*y21 + x1a*y43 - x2a*y43) + W*(-(x3a*y2a) + x4a*y2a + x2a*y3a - x4a*y3a - x2a*y4a + x3a*y4a)); const double kEpsilon = 0.0001; if(fabs(i) < kEpsilon) { i = kEpsilon* (i > 0 ? 1.0 : -1.0); } CATransform3D transform = {a/i, d/i, 0, g/i, b/i, e/i, 0, h/i, 0, 0, 1, 0, c/i, f/i, 0, 1.0}; return transform; }
这个代码我没有得分。 我所做的只是在互联网上搜集各种不完整的答案。
我们终于得到这个工作。 我们尝试了几种不同的方法，但大多数都失败了。 有些甚至在给出相同点作为input和输出时（例如，来自KennyTM的…我们一定在那里丢失了某些东西），甚至检索到一个非单一matrix。
使用OpenCV如下，我们得到一个CATransform3D准备在CAAnimation层上使用：
+ (CATransform3D)transformQuadrilateral:(Quadrilateral)origin toQuadrilateral:(Quadrilateral)destination { CvPoint2D32f *cvsrc = [self openCVMatrixWithQuadrilateral:origin]; CvMat *src_mat = cvCreateMat( 4, 2, CV_32FC1 ); cvSetData(src_mat, cvsrc, sizeof(CvPoint2D32f)); CvPoint2D32f *cvdst = [self openCVMatrixWithQuadrilateral:destination]; CvMat *dst_mat = cvCreateMat( 4, 2, CV_32FC1 ); cvSetData(dst_mat, cvdst, sizeof(CvPoint2D32f)); CvMat *H = cvCreateMat(3,3,CV_32FC1); cvFindHomography(src_mat, dst_mat, H); cvReleaseMat(&src_mat); cvReleaseMat(&dst_mat); CATransform3D transform = [self transform3DWithCMatrix:H->data.fl]; cvReleaseMat(&H); return transform; } + (CvPoint2D32f *)openCVMatrixWithQuadrilateral:(Quadrilateral)origin { CvPoint2D32f *cvsrc = (CvPoint2D32f *)malloc(4*sizeof(CvPoint2D32f)); cvsrc[0].x = origin.upperLeft.x; cvsrc[0].y = origin.upperLeft.y; cvsrc[1].x = origin.upperRight.x; cvsrc[1].y = origin.upperRight.y; cvsrc[2].x = origin.lowerRight.x; cvsrc[2].y = origin.lowerRight.y; cvsrc[3].x = origin.lowerLeft.x; cvsrc[3].y = origin.lowerLeft.y; return cvsrc; } + (CATransform3D)transform3DWithCMatrix:(float *)matrix { CATransform3D transform = CATransform3DIdentity; transform.m11 = matrix[0]; transform.m21 = matrix[1]; transform.m41 = matrix[2]; transform.m12 = matrix[3]; transform.m22 = matrix[4]; transform.m42 = matrix[5]; transform.m14 = matrix[6]; transform.m24 = matrix[7]; transform.m44 = matrix[8]; return transform; }
这是一个示例项目，它应用上面的hfossli的答案的代码，并创build一个UIView类别设置框架，并在一次调用中应用转换：
https://github.com/joshrl/FreeTransform
UIView +四边形代码：
#import <UIKit/UIKit.h> #import <QuartzCore/QuartzCore.h> @interface UIView (Quadrilateral) //Sets frame to bounding box of quad and applies transform - (void)transformToFitQuadTopLeft:(CGPoint)tl topRight:(CGPoint)tr bottomLeft:(CGPoint)bl bottomRight:(CGPoint)br; @end @implementation UIView (Quadrilateral) - (void)transformToFitQuadTopLeft:(CGPoint)tl topRight:(CGPoint)tr bottomLeft:(CGPoint)bl bottomRight:(CGPoint)br { NSAssert(CGPointEqualToPoint(self.layer.anchorPoint, CGPointZero),@"Anchor point must be (0,0)!"); CGRect boundingBox = [[self class] boundingBoxForQuadTR:tr tl:tl bl:bl br:br]; self.frame = boundingBox; CGPoint frameTopLeft = boundingBox.origin; CATransform3D transform = [[self class] rectToQuad:self.bounds quadTL:CGPointMake(tl.x-frameTopLeft.x, tl.y-frameTopLeft.y) quadTR:CGPointMake(tr.x-frameTopLeft.x, tr.y-frameTopLeft.y) quadBL:CGPointMake(bl.x-frameTopLeft.x, bl.y-frameTopLeft.y) quadBR:CGPointMake(br.x-frameTopLeft.x, br.y-frameTopLeft.y)]; self.layer.transform = transform; } + (CGRect)boundingBoxForQuadTR:(CGPoint)tr tl:(CGPoint)tl bl:(CGPoint)bl br:(CGPoint)br { CGRect boundingBox = CGRectZero; CGFloat xmin = MIN(MIN(MIN(tr.x, tl.x), bl.x),br.x); CGFloat ymin = MIN(MIN(MIN(tr.y, tl.y), bl.y),br.y); CGFloat xmax = MAX(MAX(MAX(tr.x, tl.x), bl.x),br.x); CGFloat ymax = MAX(MAX(MAX(tr.y, tl.y), bl.y),br.y); boundingBox.origin.x = xmin; boundingBox.origin.y = ymin; boundingBox.size.width = xmax - xmin; boundingBox.size.height = ymax - ymin; return boundingBox; } + (CATransform3D)rectToQuad:(CGRect)rect quadTL:(CGPoint)topLeft quadTR:(CGPoint)topRight quadBL:(CGPoint)bottomLeft quadBR:(CGPoint)bottomRight { return [self rectToQuad:rect quadTLX:topLeft.x quadTLY:topLeft.y quadTRX:topRight.x quadTRY:topRight.y quadBLX:bottomLeft.x quadBLY:bottomLeft.y quadBRX:bottomRight.x quadBRY:bottomRight.y]; } + (CATransform3D)rectToQuad:(CGRect)rect quadTLX:(CGFloat)x1a quadTLY:(CGFloat)y1a quadTRX:(CGFloat)x2a quadTRY:(CGFloat)y2a quadBLX:(CGFloat)x3a quadBLY:(CGFloat)y3a quadBRX:(CGFloat)x4a quadBRY:(CGFloat)y4a { CGFloat X = rect.origin.x; CGFloat Y = rect.origin.y; CGFloat W = rect.size.width; CGFloat H = rect.size.height; CGFloat y21 = y2a - y1a; CGFloat y32 = y3a - y2a; CGFloat y43 = y4a - y3a; CGFloat y14 = y1a - y4a; CGFloat y31 = y3a - y1a; CGFloat y42 = y4a - y2a; CGFloat a = -H*(x2a*x3a*y14 + x2a*x4a*y31 - x1a*x4a*y32 + x1a*x3a*y42); CGFloat b = W*(x2a*x3a*y14 + x3a*x4a*y21 + x1a*x4a*y32 + x1a*x2a*y43); CGFloat c = H*X*(x2a*x3a*y14 + x2a*x4a*y31 - x1a*x4a*y32 + x1a*x3a*y42) - H*W*x1a*(x4a*y32 - x3a*y42 + x2a*y43) - W*Y*(x2a*x3a*y14 + x3a*x4a*y21 + x1a*x4a*y32 + x1a*x2a*y43); CGFloat d = H*(-x4a*y21*y3a + x2a*y1a*y43 - x1a*y2a*y43 - x3a*y1a*y4a + x3a*y2a*y4a); CGFloat e = W*(x4a*y2a*y31 - x3a*y1a*y42 - x2a*y31*y4a + x1a*y3a*y42); CGFloat f = -(W*(x4a*(Y*y2a*y31 + H*y1a*y32) - x3a*(H + Y)*y1a*y42 + H*x2a*y1a*y43 + x2a*Y*(y1a - y3a)*y4a + x1a*Y*y3a*(-y2a + y4a)) - H*X*(x4a*y21*y3a - x2a*y1a*y43 + x3a*(y1a - y2a)*y4a + x1a*y2a*(-y3a + y4a))); CGFloat g = H*(x3a*y21 - x4a*y21 + (-x1a + x2a)*y43); CGFloat h = W*(-x2a*y31 + x4a*y31 + (x1a - x3a)*y42); CGFloat i = W*Y*(x2a*y31 - x4a*y31 - x1a*y42 + x3a*y42) + H*(X*(-(x3a*y21) + x4a*y21 + x1a*y43 - x2a*y43) + W*(-(x3a*y2a) + x4a*y2a + x2a*y3a - x4a*y3a - x2a*y4a + x3a*y4a)); const double kEpsilon = 0.0001; if(fabs(i) < kEpsilon) { i = kEpsilon* (i > 0 ? 1.0 : -1.0); } CATransform3D transform = {a/i, d/i, 0, g/i, b/i, e/i, 0, h/i, 0, 0, 1, 0, c/i, f/i, 0, 1.0}; return transform; } @end
JoshRL 100％感谢，这是JoshRL的Swift版本。
这已经完全和完全debugging。 遭受“Swift太长”问题的行被重构和破坏testing。
它在大批量生产中工作完美无瑕。 希望能帮助别人。
不能更容易使用。 示例显示如何在下面的Swift中使用。
2016年Swift版…充分，工作，复制和粘贴解决scheme
// JoshQuadView in Swift // from: https://stackoverflow.com/a/18606029/294884 // NB: JoshRL uses the ordering convention // "topleft, topright, bottomleft, bottomright" // which is different from "clockwise from topleft". // Note: is not meant to handle concave. import UIKit class JoshQuadView:UIView { func transformToFitQuadTopLeft(tl:CGPoint,tr:CGPoint,bl:CGPoint,br:CGPoint) { guard CGPointEqualToPoint(self.layer.anchorPoint, CGPointZero) else { print("suck");return } let b:CGRect = boundingBoxForQuadTR(tl, tr, bl, br) self.frame = b self.layer.transform = rectToQuad( self.bounds, CGPointMake(tl.xb.origin.x, tl.yb.origin.y), CGPointMake(tr.xb.origin.x, tr.yb.origin.y), CGPointMake(bl.xb.origin.x, bl.yb.origin.y), CGPointMake(br.xb.origin.x, br.yb.origin.y) ) } func boundingBoxForQuadTR( tl:CGPoint, _ tr:CGPoint, _ bl:CGPoint, _ br:CGPoint )->(CGRect) { var b:CGRect = CGRectZero let xmin:CGFloat = min(min(min(tr.x, tl.x), bl.x),br.x); let ymin:CGFloat = min(min(min(tr.y, tl.y), bl.y),br.y); let xmax:CGFloat = max(max(max(tr.x, tl.x), bl.x),br.x); let ymax:CGFloat = max(max(max(tr.y, tl.y), bl.y),br.y); b.origin.x = xmin b.origin.y = ymin b.size.width = xmax - xmin b.size.height = ymax - ymin return b; } func rectToQuad( rect:CGRect, _ topLeft:CGPoint, _ topRight:CGPoint, _ bottomLeft:CGPoint, _ bottomRight:CGPoint )->(CATransform3D) { return rectToQuad(rect, topLeft.x, topLeft.y, topRight.x, topRight.y, bottomLeft.x, bottomLeft.y, bottomRight.x, bottomRight.y) } func rectToQuad( rect:CGRect, _ x1a:CGFloat, _ y1a:CGFloat, _ x2a:CGFloat, _ y2a:CGFloat, _ x3a:CGFloat, _ y3a:CGFloat, _ x4a:CGFloat, _ y4a:CGFloat )->(CATransform3D) { let X = rect.origin.x; let Y = rect.origin.y; let W = rect.size.width; let H = rect.size.height; let y21 = y2a - y1a; let y32 = y3a - y2a; let y43 = y4a - y3a; let y14 = y1a - y4a; let y31 = y3a - y1a; let y42 = y4a - y2a; let a = -H*(x2a*x3a*y14 + x2a*x4a*y31 - x1a*x4a*y32 + x1a*x3a*y42); let b = W*(x2a*x3a*y14 + x3a*x4a*y21 + x1a*x4a*y32 + x1a*x2a*y43); // let c = H*X*(x2a*x3a*y14 + x2a*x4a*y31 - x1a*x4a*y32 + x1a*x3a*y42) - H*W*x1a*(x4a*y32 - x3a*y42 + x2a*y43) - W*Y*(x2a*x3a*y14 + x3a*x4a*y21 + x1a*x4a*y32 + x1a*x2a*y43); // Could be too long for Swift. Replaced with four lines: let c0 = -H*W*x1a*(x4a*y32 - x3a*y42 + x2a*y43) let cx = H*X*(x2a*x3a*y14 + x2a*x4a*y31 - x1a*x4a*y32 + x1a*x3a*y42) let cy = -W*Y*(x2a*x3a*y14 + x3a*x4a*y21 + x1a*x4a*y32 + x1a*x2a*y43) let c = c0 + cx + cy let d = H*(-x4a*y21*y3a + x2a*y1a*y43 - x1a*y2a*y43 - x3a*y1a*y4a + x3a*y2a*y4a); let e = W*(x4a*y2a*y31 - x3a*y1a*y42 - x2a*y31*y4a + x1a*y3a*y42); // let f = -(W*(x4a*(Y*y2a*y31 + H*y1a*y32) - x3a*(H + Y)*y1a*y42 + H*x2a*y1a*y43 + x2a*Y*(y1a - y3a)*y4a + x1a*Y*y3a*(-y2a + y4a)) - H*X*(x4a*y21*y3a - x2a*y1a*y43 + x3a*(y1a - y2a)*y4a + x1a*y2a*(-y3a + y4a))); // Is too long for Swift. Replaced with four lines: let f0 = -W*H*(x4a*y1a*y32 - x3a*y1a*y42 + x2a*y1a*y43) let fx = H*X*(x4a*y21*y3a - x2a*y1a*y43 - x3a*y21*y4a + x1a*y2a*y43) let fy = -W*Y*(x4a*y2a*y31 - x3a*y1a*y42 - x2a*y31*y4a + x1a*y3a*y42) let f = f0 + fx + fy let g = H*(x3a*y21 - x4a*y21 + (-x1a + x2a)*y43); let h = W*(-x2a*y31 + x4a*y31 + (x1a - x3a)*y42); // let i = W*Y*(x2a*y31 - x4a*y31 - x1a*y42 + x3a*y42) + H*(X*(-(x3a*y21) + x4a*y21 + x1a*y43 - x2a*y43) + W*(-(x3a*y2a) + x4a*y2a + x2a*y3a - x4a*y3a - x2a*y4a + x3a*y4a)); // Is too long for Swift. Replaced with four lines: let i0 = H*W*(x3a*y42 - x4a*y32 - x2a*y43) let ix = H*X*(x4a*y21 - x3a*y21 + x1a*y43 - x2a*y43) let iy = W*Y*(x2a*y31 - x4a*y31 - x1a*y42 + x3a*y42) var i = i0 + ix + iy let kEpsilon:CGFloat = 0.0001; if(fabs(i) < kEpsilon) { i = kEpsilon * (i > 0 ? 1.0 : -1.0); } return CATransform3D(m11:a/i, m12:d/i, m13:0, m14:g/i, m21:b/i, m22:e/i, m23:0, m24:h/i, m31:0, m32:0, m33:1, m34:0, m41:c/i, m42:f/i, m43:0, m44:1.0) } }
在Swift中使用：
假设你有一个容器视图“QuadScreen”。
放下你想要拉伸的视图将成为场景中的JoshQuadView。 在这里的例子“jqv”。
只需在场景中放置四个angular落手柄（即图像），即处理图标的PNG。 下面的代码完全处理这些句柄; 只需按照代码中的注释说明如何在故事板中轻松设置即可。
这只是执行拉伸的一行代码：
class QuadScreen:UIViewController { // sit your JoshQuadView in this view @IBOutlet var jqv:JoshQuadView! // simply have four small subview views, "handles" // with an icon on them (perhaps a small circle) // and put those over the four corners of the jqv // NOTE numbered CLOCKWISE from top left here: @IBOutlet var handle1:UIView! @IBOutlet var handle2:UIView! @IBOutlet var handle3:UIView! @IBOutlet var handle4:UIView! // put a pan recognizer on each handle, action goes to here // (for the pan recognizers, set cancels-in-view as needed // if you, example, highlight them on touch in their class) @IBAction func dragHandle(p:UIPanGestureRecognizer!) { let tr = p.translationInView(p.view) p.view!.center.x += tr.x p.view!.center.y += tr.y p.setTranslation(CGPointZero, inView: p.view) jqv.transformToFitQuadTopLeft( handle1.center, tr: handle2.center, bl: handle4.center, br: handle3.center ) // it's that simple, there's nothing else to do p.setTranslation(CGPointZero, inView: p.view) } override func viewDidLayoutSubviews() { // don't forget to do this....is critical. jqv.layer.anchorPoint = CGPointMake(0, 0) }
作为一个好奇心，为了谷歌的利益，这是可笑的容易做到这一点
Android的
他们有一个内置的重塑多边形的命令。 这个优秀的答案有复制和粘贴代码： https ： //stackoverflow.com/a/34667015/294884
锚点独立解决scheme：
我真的很喜欢@joshrl回答他在哪里做了一个类“UIView +四边形”，它使用@ hfossli上面最好的答案。 但是，多次调用类别来更改四边形失败，代码要求AnchorPoint左上angular。
我的解决scheme（来自他们的）：
- 帐户的任何AnchorPoint
- 允许改变四边形
UIView + Quadrilateral.h ：
#import <UIKit/UIKit.h> #import <QuartzCore/QuartzCore.h> @interface UIView (Quadrilateral) //Sets frame to bounding box of quad and applies transform - (void)transformToFitQuadTopLeft:(CGPoint)tl topRight:(CGPoint)tr bottomLeft:(CGPoint)bl bottomRight:(CGPoint)br; @end
UIView + Quadrilateral.m ：
#import "UIView+Quadrilateral.h" @implementation UIView (Quadrilateral) - (void)transformToFitQuadTopLeft:(CGPoint)tl topRight:(CGPoint)tr bottomLeft:(CGPoint)bl bottomRight:(CGPoint)br { CGRect boundingBox = [[self class] boundingBoxForQuadTR:tr tl:tl bl:bl br:br]; self.layer.transform = CATransform3DIdentity; // keeps current transform from interfering self.frame = boundingBox; CGPoint frameTopLeft = boundingBox.origin; CATransform3D transform = [[self class] rectToQuad:self.bounds quadTL:CGPointMake(tl.x-frameTopLeft.x, tl.y-frameTopLeft.y) quadTR:CGPointMake(tr.x-frameTopLeft.x, tr.y-frameTopLeft.y) quadBL:CGPointMake(bl.x-frameTopLeft.x, bl.y-frameTopLeft.y) quadBR:CGPointMake(br.x-frameTopLeft.x, br.y-frameTopLeft.y)]; // To account for anchor point, we must translate, transform, translate CGPoint anchorPoint = self.layer.position; CGPoint anchorOffset = CGPointMake(anchorPoint.x - boundingBox.origin.x, anchorPoint.y - boundingBox.origin.y); CATransform3D transPos = CATransform3DMakeTranslation(anchorOffset.x, anchorOffset.y, 0.); CATransform3D transNeg = CATransform3DMakeTranslation(-anchorOffset.x, -anchorOffset.y, 0.); CATransform3D fullTransform = CATransform3DConcat(CATransform3DConcat(transPos, transform), transNeg); // Now we set our transform self.layer.transform = fullTransform; } + (CGRect)boundingBoxForQuadTR:(CGPoint)tr tl:(CGPoint)tl bl:(CGPoint)bl br:(CGPoint)br { CGRect boundingBox = CGRectZero; CGFloat xmin = MIN(MIN(MIN(tr.x, tl.x), bl.x),br.x); CGFloat ymin = MIN(MIN(MIN(tr.y, tl.y), bl.y),br.y); CGFloat xmax = MAX(MAX(MAX(tr.x, tl.x), bl.x),br.x); CGFloat ymax = MAX(MAX(MAX(tr.y, tl.y), bl.y),br.y); boundingBox.origin.x = xmin; boundingBox.origin.y = ymin; boundingBox.size.width = xmax - xmin; boundingBox.size.height = ymax - ymin; return boundingBox; } + (CATransform3D)rectToQuad:(CGRect)rect quadTL:(CGPoint)topLeft quadTR:(CGPoint)topRight quadBL:(CGPoint)bottomLeft quadBR:(CGPoint)bottomRight { return [self rectToQuad:rect quadTLX:topLeft.x quadTLY:topLeft.y quadTRX:topRight.x quadTRY:topRight.y quadBLX:bottomLeft.x quadBLY:bottomLeft.y quadBRX:bottomRight.x quadBRY:bottomRight.y]; } + (CATransform3D)rectToQuad:(CGRect)rect quadTLX:(CGFloat)x1a quadTLY:(CGFloat)y1a quadTRX:(CGFloat)x2a quadTRY:(CGFloat)y2a quadBLX:(CGFloat)x3a quadBLY:(CGFloat)y3a quadBRX:(CGFloat)x4a quadBRY:(CGFloat)y4a { CGFloat X = rect.origin.x; CGFloat Y = rect.origin.y; CGFloat W = rect.size.width; CGFloat H = rect.size.height; CGFloat y21 = y2a - y1a; CGFloat y32 = y3a - y2a; CGFloat y43 = y4a - y3a; CGFloat y14 = y1a - y4a; CGFloat y31 = y3a - y1a; CGFloat y42 = y4a - y2a; CGFloat a = -H*(x2a*x3a*y14 + x2a*x4a*y31 - x1a*x4a*y32 + x1a*x3a*y42); CGFloat b = W*(x2a*x3a*y14 + x3a*x4a*y21 + x1a*x4a*y32 + x1a*x2a*y43); CGFloat c = H*X*(x2a*x3a*y14 + x2a*x4a*y31 - x1a*x4a*y32 + x1a*x3a*y42) - H*W*x1a*(x4a*y32 - x3a*y42 + x2a*y43) - W*Y*(x2a*x3a*y14 + x3a*x4a*y21 + x1a*x4a*y32 + x1a*x2a*y43); CGFloat d = H*(-x4a*y21*y3a + x2a*y1a*y43 - x1a*y2a*y43 - x3a*y1a*y4a + x3a*y2a*y4a); CGFloat e = W*(x4a*y2a*y31 - x3a*y1a*y42 - x2a*y31*y4a + x1a*y3a*y42); CGFloat f = -(W*(x4a*(Y*y2a*y31 + H*y1a*y32) - x3a*(H + Y)*y1a*y42 + H*x2a*y1a*y43 + x2a*Y*(y1a - y3a)*y4a + x1a*Y*y3a*(-y2a + y4a)) - H*X*(x4a*y21*y3a - x2a*y1a*y43 + x3a*(y1a - y2a)*y4a + x1a*y2a*(-y3a + y4a))); CGFloat g = H*(x3a*y21 - x4a*y21 + (-x1a + x2a)*y43); CGFloat h = W*(-x2a*y31 + x4a*y31 + (x1a - x3a)*y42); CGFloat i = W*Y*(x2a*y31 - x4a*y31 - x1a*y42 + x3a*y42) + H*(X*(-(x3a*y21) + x4a*y21 + x1a*y43 - x2a*y43) + W*(-(x3a*y2a) + x4a*y2a + x2a*y3a - x4a*y3a - x2a*y4a + x3a*y4a)); const double kEpsilon = 0.0001; if(fabs(i) < kEpsilon) { i = kEpsilon* (i > 0 ? 1.0 : -1.0); } CATransform3D transform = {a/i, d/i, 0, g/i, b/i, e/i, 0, h/i, 0, 0, 1, 0, c/i, f/i, 0, 1.0}; return transform; } @end
上面的类别是如此简单和优雅，它应该包含在每个工具箱中。 感谢上述代码的最终来源。 不应该给我信任。
如果你的新四边形是一个平行四边形，那么这就叫做“剪切”，用CGAffineTransform可以很容易地完成。 请参阅Jeff LaMarche的优秀文章CGAffineTransform 1.1 。
如果您的新四边形不是平行四边形，请参阅以下问题了解如何应用CATransform3D： iPhone图像拉伸（倾斜） 。
