Question

What I am doing is on every touch event I am creating an image from unsigned char *. Here is my function

-(void)paint:(ImageWarper::WarpedImage *)warpedImg isCircleRequired:(bool)doDrawCircle atPoint:(CGPoint)pt{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
if(!mWarper) 
    return;
unsigned char *pixelData = warpedImg->Image.Data;
int imageHeight  = warpedImg->Image.Height;
int scanWidth = warpedImg->Image.ScanWidth;
int imageWidth = warpedImg->Image.Width;
CGDataProviderRef provider = CGDataProviderCreateWithData(
                                                          NULL, 
                                                          pixelData, 
                                                          imageHeight * scanWidth, 
                                                          (CGDataProviderReleaseDataCallback)&freeRawData); 
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
int bytesPerPixel = warpedImg->Image.Bpp;
CGImageRef imageRef = CGImageCreate(imageWidth,
                                    imageHeight,
                                    BitsPerComponent,
                                    bytesPerPixel * BitsPerComponent,
                                    scanWidth,
                                    colorSpaceRef,
                                    bitmapInfo,
                                    provider,
                                    NULL,
                                    YES,
                                    renderingIntent);
if(!imageRef)
    return;

UIImage *uiImage = [UIImage imageWithCGImage:imageRef];
imgScrollView.imgView.image = uiImage;
UIGraphicsBeginImageContext(mbmpImage.size); 
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(ctx, 1.5);
CGContextSetStrokeColorWithColor(ctx, [UIColor whiteColor].CGColor);

[mbmpImage drawInRect:CGRectMake(0, 0, mbmpImage.size.width, mbmpImage.size.height)];

[uiImage drawInRect:CGRectMake(warpedImg->Position.X, warpedImg->Position.Y, warpedImg->Image.Width, warpedImg->Image.Height)];         

if(doDrawCircle){
    [mbmpImage release];
    mbmpImage = [UIGraphicsGetImageFromCurrentImageContext() retain];       

    CGContextStrokeEllipseInRect(ctx,CGRectMake(pt.x - mRadius, pt.y - mRadius, mRadius*2, mRadius*2));
}
else{
    [mbmpImage release];
    mbmpImage = [UIGraphicsGetImageFromCurrentImageContext() retain];
}
UIImage * resultingImage = [UIGraphicsGetImageFromCurrentImageContext() retain];    

UIGraphicsEndImageContext();
imgScrollView.imgView.image =  resultingImage ;

if(!doDrawCircle)   {   
    [mbmpImage release];
    mbmpImage = [resultingImage retain];

}
if(doDrawCircle){
    CGPoint pt2 = [self.view convertPoint:pt fromView:imgScrollView];
    imgPreview.hidden = NO;
    [self addText:mbmpImage text: @"+" atPoint:pt atRect:(warpedImg->Position.X, warpedImg->Position.Y, warpedImg->Image.Width, warpedImg->Image.Height)];
}
else{
    [popoverController dismissPopoverAnimated:YES];
}
[resultingImage release];
CGColorSpaceRelease(colorSpaceRef);
CGDataProviderRelease(provider);
CGImageRelease(imageRef);

[pool drain];
 }

This Function is called as follows:

NSMutableDictionary *d = [[NSMutableDictionary alloc] initWithObjectsAndKeys:[NSValue valueWithPointer:wp1],@"warper", @"YES",@"isCircleRequired",
                                  [NSValue valueWithCGPoint:location],@"point",nil];
[self performSelector:@selector(paintDic:) withObject:d];
[d release];
wp1 = nil;

-(void)paintDic:(NSMutableDictionary *)dictionary{
ImageWarper::WarpedImage *wp1 =  (ImageWarper::WarpedImage *)[[dictionary objectForKey:@"warper"] pointerValue];
[self paint:wp1
    isCircleRequired:[dictionary objectForKey:@"isCircleRequired"] 
    atPoint:[[dictionary objectForKey:@"point"] CGPointValue]];
}

I am using following callback function to release data.

void freeRawData(void *info, const void *data, size_t size) {
data = nil;
}

Can any one help me how do I optimize the speed of this. It is working fine on new iphone but not older iphones.

I am calling paint in perform selector so that I dont get hold of execution while it completes its creation of images.
Also any help to create images directly from raw data i.e. unsigned char * will be appreciated.

Answer 1

Before you attempt any optimizations, measure where you spend your time. Instruments’ performance tools will help you here.

Off the top of my head, I see a bit of stuff that really need not be there in the code you showed:

• First and foremost: if you can get away with drawing less often, then do that.
• The probability that your device’s colorspace changes during the life-time of your app can be neglected — cacheing the color space in a static variable might shave some time off this code.
• You’re already doing CG-level drawing — not creating UIImages but using CGContextDrawImage instead might save you quite some time, too.
• If you need not support iOS 3, use dispatch_async instead of performSelector:withObject: — that way you don’t need to wrap and unwrap your non-object types.

But like I said:

Measure your app before performing any optimizations!

Including these measures, I also reduced the number of run loops this code was executed. This measure improved performance of my app drastically.