如何使用CGContextDrawImage？

Question

我需要一些使用CGContextDrawImage的帮助。我有以下代码，它将创建一个位图上下文，并将像素数据转换为CGImageRef。现在，我需要使用CGContextDrawImage显示该图像。我不是很清楚我应该如何使用它。以下是我的代码：

- (void)drawBufferWidth:(int)width height:(int)height pixels:(unsigned char*)pixels
    {
     const int area = width *height;
     const int componentsPerPixel = 4;
     unsigned char pixelData[area * componentsPerPixel];

     for(int i = 0; i<area; i++)
     {
          const int offset = i * componentsPerPixel;
          pixelData[offset] = pixels[0];
          pixelData[offset+1] = pixels[1];
          pixelData[offset+2] = pixels[2];
          pixelData[offset+3] = pixels[3];
     }

     const size_t BitsPerComponent = 8;
     const size_t BytesPerRow=((BitsPerComponent * width) / 8) * componentsPerPixel;
     CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
     CGContextRef gtx = CGBitmapContextCreate(pixelData, width, height, BitsPerComponent, BytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast);
     CGImageRef myimage = CGBitmapContextCreateImage(gtx);

     //What code should go here to display the image?

     CGContextRelease(gtx);
     CGImageRelease(myimage);

}

任何帮助或一段示例代码都会很棒。提前感谢！

Answer 1

创建名为MyDrawingView.h的文件

#import <UIKit/UIKit.h>
#import <QuartzCore/QuartzCore.h>

@interface MyDrawingView : UIView
{
}

@end

现在创建一个名为MyDrawingView.m的文件

#import "MyChartView.h"

@implementation MyDrawingView

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code

        // Write your initialization code if any.

    }
    return self;
}

// Only override drawRect: if you perform custom drawing.
- (void)drawRect:(CGRect)rect
{
    // Drawing code

    // Create Current Context To Draw
    CGContextRef context = UIGraphicsGetCurrentContext();

    UIImage *image = [UIImage imageNamed:@"image.jpg"];
    // Draws your image at given poing
    [image drawAtPoint:CGPointMake(10, 10)];
}

//现在在您的视图中使用它

 #import "MyChartView.h"    

 MyDrawingView *drawView = [[MyDrawingView alloc] initWithFrame:CGRectMake(0, 0, 200, 200)];
 [self.view addSubview:drawView];


 // whenever you want to update that view call
 [drawView setNeedsDisplay];

//这是你处理(绘制)图像的方法

- (void)drawBufferWidth:(int)width height:(int)height pixels:(unsigned char*)pixels
{
    const int area = width *height;
    const int componentsPerPixel = 4;
    unsigned char pixelData[area * componentsPerPixel];

    for(int i = 0; i<area; i++)
    {
        const int offset = i * componentsPerPixel;
        pixelData[offset] = pixels[0];
        pixelData[offset+1] = pixels[1];
        pixelData[offset+2] = pixels[2];
        pixelData[offset+3] = pixels[3];
    }

    const size_t BitsPerComponent = 8;
    const size_t BytesPerRow=((BitsPerComponent * width) / 8) * componentsPerPixel;
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef gtx = CGBitmapContextCreate(pixelData, width, height, BitsPerComponent, BytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast);
    CGImageRef myimage = CGBitmapContextCreateImage(gtx);

    // Convert to UIImage
    UIImage *image = [UIImage imageWithCGImage:myimage];

    // Create a rect to display
    CGRect imageRect = CGRectMake(0, 0, image.size.width, image.size.height);

    // Here is the Two Snnipets to draw image
    CGContextRef context = UIGraphicsGetCurrentContext();

    // Transform image
    CGContextTranslateCTM(context, 0, image.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    // Finaly Draw your image
    CGContextDrawImage(context, imageRect, image.CGImage);

    // You can also use following to draw your image in 'drawRect' method
    //    [[UIImage imageWithCGImage:myimage] drawInRect:CGRectMake(0, 0, 145, 15)];

    CGContextRelease(gtx);
    CGImageRelease(myimage);
}

Answer 2

如果有其他人处理这个问题，请尝试将以下代码插入到Ereka的代码中。Dipen的解决方案似乎有点过了。在注释“//什么代码应该在这里显示图像”之后，放入以下代码：

CGRect myContextRect = CGRectMake (0, 0, width, height);
CGContextDrawImage (gtx, myContextRect, myimage);
CGImageRef imageRef = CGBitmapContextCreateImage(gtx);
UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
UIImageView *imgView = [[UIImageView alloc] initWithImage:finalImage];
[self.view addSubview:imgView];