iOS如何有效地執行cgimage的旋轉（最多125幀）？

Question

我有兩個圖像，我們稱它們爲圖像A和圖像B.我試圖旋轉和縮放圖像A，並在特定位置將其繪製在圖像B的頂部。

我使用下面的功能和方法： 1.旋轉和縮放我的圖像 2.將圖像A繪製到圖像B的特定位置。

此代碼工作正常，但相當緩慢，有沒有辦法改善它？

功能旋轉和縮放：

CGImageRef rotateAndScaleImageCreate(const CGImageRef cgImage, const CGFloat radians,const CGFloat scalefactor){ 
CGImageRef rotatedImageRef = NULL; 

const CGFloat originalWidth = CGImageGetWidth(cgImage)*scalefactor; 
const CGFloat originalHeight = CGImageGetHeight(cgImage)*scalefactor; 

const CGRect imgRect = (CGRect){.origin.x = 0.0f, .origin.y = 0.0f, .size.width = originalWidth, .size.height = originalHeight}; 
const CGRect rotatedRect = CGRectApplyAffineTransform(imgRect, CGAffineTransformMakeRotation(radians)); 

/// Create an ARGB bitmap context 
CGContextRef bmContext = NYXImageCreateARGBBitmapContext(rotatedRect.size.width, rotatedRect.size.height, 0); 
if (!bmContext) 
    return nil; 

/// Rotation happen here 
CGContextTranslateCTM(bmContext, +(rotatedRect.size.width * 0.5f), +(rotatedRect.size.height * 0.5f)); 
CGContextRotateCTM(bmContext, radians); 

/// Draw the image in the bitmap context 
CGContextDrawImage(bmContext, (CGRect){.origin.x = -originalWidth * 0.5f, .origin.y = -originalHeight * 0.5f, .size.width = originalWidth, .size.height = originalHeight}, cgImage); 

/// Create an image object from the context 
rotatedImageRef = CGBitmapContextCreateImage(bmContext); 

/// Cleanup 
//CGImageRelease(rotatedImageRef); 
CGContextRelease(bmContext); 

return rotatedImageRef; 
} 

方法在特定地點的另一個圖像中繪製圖像：

-(UIImage*) PositionImage:(CGImageRef)image backgroundImage:(CGImageRef)backgroundImage atPointX:(float)X pointY:(float)Y withScale:(float)scale andRotation:(float)rotation{ 


////////////////////////////////////////// 

CGLayerRef   layer; 

CGImageRef   resultImage; 

CGContextRef  context, layerContext; 
void    *bitmapData; 
CGColorSpaceRef  colorSpace; 
CGSize    canvasSize; 

int     bitmapByteCount; 
int     bitmapBytesPerRow; 

//Get the background image 
//UIImage * backgroundImg = [UIImage imageNamed:@"Mask-Inverted.png"]; 

//Initialize the canvas size! 
canvasSize = CGSizeMake(480,640);//[backgroundImg size]; 


// 
bitmapBytesPerRow = (canvasSize.width * 4); 
bitmapByteCount  = (bitmapBytesPerRow * canvasSize.height); 

//Create the color space 
colorSpace = CGColorSpaceCreateDeviceRGB(); 

bitmapData = malloc(bitmapByteCount); 

//Check the the buffer is alloc'd 
if(bitmapData == NULL){ 
    NSLog(@"Buffer could not be alloc'd"); 
} 

//Create the context 
context = CGBitmapContextCreate(bitmapData, canvasSize.width, canvasSize.height, 8, bitmapBytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast); 

if(context == NULL){ 
    NSLog(@"Context could not be created"); 
} 


///Create the Layer 
layer = CGLayerCreateWithContext(context, canvasSize, NULL); 

if(layer == NULL){ 
    NSLog(@"Layer could not be created"); 
} 

///Create the layer Context 
layerContext = CGLayerGetContext(layer); 

if(layerContext == NULL){ 
    NSLog(@"No Layer context"); 
} 


//Draw the image background into the bitmap context 
CGContextDrawImage(context, CGRectMake(0.0f,0.0f,480,640),backgroundImage); 

//Rotate and Scale Image 
CGImageRef rotatedImage =rotateAndScaleImageCreate(image,rotation,scale); 

//Draw a image on the layer 
CGContextDrawImage(layerContext,CGRectMake(0,0,CGImageGetWidth(rotatedImage),CGImageGetHeight(rotatedImage)),rotatedImage); 
CGImageRelease(rotatedImage); 

//Draw the layer in the context at the coordinate 
CGContextDrawLayerAtPoint(context, CGPointMake(X-CGImageGetWidth(rotatedImage)*0.5f, Y-CGImageGetHeight(rotatedImage)*0.5f), layer); 
CGLayerRelease(layer); 

//Get the result image 
resultImage = CGBitmapContextCreateImage(context); 
CGContextRelease(context); 

//Cleanup 
free(bitmapData); 
CGColorSpaceRelease(colorSpace); 
//Create UIImage 
UIImage *imageReturned = [UIImage imageWithCGImage:resultImage]; 
CGImageRelease(resultImage); 
return imageReturned; 

} 

Answer 1

如果你在同一時間創造大量的圖片，再利用相同的CGContext。另外，請勿創建新的旋轉圖像;在現有的上下文中旋轉圖像。

基本上，你只需要創建一次CGContext一次，不管你最終制作了多少圖片。這應該會顯着加快速度。