How to use CGContextDrawImage? - quartz-2d

Question

I need some help using the CGContextDrawImage. I have the following code which will create a Bitmap context and convert the pixel data to CGImageRef. Now I need to display that image using CGContextDrawImage. I'm not very clear on how I'm supposed to use that. The following is my code:
- (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);
}
Any help or a sample piece of code would be great. Thanks in advance!

Answer 1

Create a file named : MyDrawingView.h
#import <UIKit/UIKit.h>
#import <QuartzCore/QuartzCore.h>
#interface MyDrawingView : UIView
{
}
#end
now create a file named : MyDrawingView.m
#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)];
}
// now to use it in your view
#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];
// its your method to process(draw) image
- (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

If there is anyone else dealing with this problem, please try inserting the following code into Ereka's code. Dipen's solution seems a little too much. Right after the comment "//What code should go here to display the image," put the following code:
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];