iOS 实现图片自定义变换

 1 -(void)changeImageByPoints:(NSArray *)pointArray{
 2     UIImage * image = _image; //全局需要变换的图片
 3     float width = CGImageGetWidth(image.CGImage);
 4     float height = CGImageGetHeight(image.CGImage);
 5     
 6     CGPoint p0 = [pointArray[0]CGPointValue];
 7     CGPoint p1 = [pointArray[1]CGPointValue];
 8     CGPoint p2 = [pointArray[2]CGPointValue];
 9     CGPoint p3 = [pointArray[3]CGPointValue];
10     
11     //痛觉相对于父视图的绝对4个顶点计算出新的宽度和高度
12     float minLeft = MIN(MIN(p0.x, p1.x), MIN(p2.x, p3.x));
13     float minTop = MIN(MIN(p0.y, p1.y), MIN(p2.y, p3.y));
14     float shapW = KINT((MAX(MAX(p0.x, p1.x), MAX(p2.x, p3.x)) - minLeft));
15     float shapH = KINT((MAX(MAX(p0.y, p1.y), MAX(p2.y, p3.y)) - minTop));
16     
17     //change point relative to image not superview
18     p0.x = p0.x - minLeft;
19     p1.x = p1.x - minLeft;
20     p2.x = p2.x - minLeft;
21     p3.x = p3.x - minLeft;
22     p0.y = p0.y - minTop;
23     p1.y = p1.y - minTop;
24     p2.y = p2.y - minTop;
25     p3.y = p3.y - minTop;   
26     
27     //创建一个bitmapcontext
28     if (!_first) {
29         needData = malloc(KINT(width)* KINT(height) * 4);
30         CGContextRef imageContext = CGBitmapContextCreate(needData, width, height, 8, width * 4, CGImageGetColorSpace(image.CGImage), CGImageGetAlphaInfo(image.CGImage));
31         CGContextDrawImage(imageContext, CGRectMake(0, 0, width, height), image.CGImage);
32         data = malloc(KINT(width) * KINT(height) * 4);
33         data = CGBitmapContextGetData(imageContext);
34         _first = YES;
35     }  
36     
37     //初始化新的图片需要的data
38     unsigned char* shapeData = malloc(shapW * shapH * 4);
39     for (int i = 0; i < shapH -1; i ++) {
40         for (int j = 0; j < shapW -1; j++) {
41             int offset = (i * shapW + j) * 4;
42             shapeData[offset] = 255;
43             shapeData[offset + 1] = 255;
44             shapeData[offset + 2] = 255;
45             shapeData[offset + 3] = 255;
46         }
47     }
48  
49     //给data添加对应的像素值
50     for (int i = 0; i < height -1; i++) {
51         for (int j = 0; j < width -1; j++) {
52             CGPoint originPoint = CGPointMake(j, i);
53             int originOffset = (i * width + j) * 4;
54             // 计算原图每个点在新图中的位置
55             float xFunc = (float)originPoint.x / (float)width;
56             float yFunc = (float)originPoint.y / (float)height;
57                    
58             float delx = (p1.x - p0.x) * xFunc;
59             float dely = (p1.y - p0.y) * xFunc;
60             CGPoint topPoint = CGPointMake(p0.x + delx, p0.y + dely);
61             
62             delx = (p2.x - p3.x) * xFunc;
63             dely = (p2.y - p3.y) * xFunc;
64             CGPoint bottomPoint = CGPointMake(p3.x + delx, p3.y + dely);
65             
66             delx = (bottomPoint.x - topPoint.x) * yFunc;
67             dely = (bottomPoint.y - topPoint.y) * yFunc;
68             
69             CGPoint newPoint = CGPointMake(topPoint.x + delx, topPoint.y + dely);
70             
71             int newOffset = ((KINT(newPoint.y) * shapW + KINT(newPoint.x))) * 4;
72             
73             //give shapeView new value
74             shapeData[newOffset] = data[originOffset];
75             shapeData[newOffset + 1] = data[originOffset + 1];
76             shapeData[newOffset + 2] = data[originOffset + 2];
77             shapeData[newOffset + 3] = data[originOffset + 3];
78             
79         }
80     }
81     //创建新图片
82     CGContextRef newContext = CGBitmapContextCreate(shapeData, shapW, shapH, 8, shapW * 4, CGImageGetColorSpace(image.CGImage), CGImageGetAlphaInfo(image.CGImage));
83     
84     CGImageRef cgImage = CGBitmapContextCreateImage(newContext);
85     _imageView.image = [UIImage imageWithCGImage:cgImage ];  //这个_imageView就是贴上viewcontroller上面的UIImageview
86     _imageView.frame = CGRectMake(minLeft, minTop, shapW, shapH);
87     CGContextRelease(newContext);
88     CGImageRelease(cgImage);
89     free(shapeData);
90 }