I use UIScrollView, which zooms and scrolls UIImageView, which contains UIImage, which take pixels from CGImage.
Size of CGImage may be about 5000x2000 pixels
1) Is this a correct way to zoom and scroll big image?
Some logic may change periodically some region(rect) in that CGImage
2) How can i change individuall pixels in CGImage inplace without heawy processor usage (entire image recreation)?
my solution:
I create CGBitmapContext for storing big image at XRGB-format.
Subclass UIView for override drawRect: which represent my image
periodically updates do so:
update some rect
invoke [setNeedsDisplayInRect: rect]
in [drawRect: rect] do:
CGContextRef g = UIGraphicsGetCurrentContext();
CGImageRef imgAll = CGBitmapContextCreateImage( m_BmpContext );
CGImageRef imgRect = CGImageCreateWithImageInRect( imgAll, rect );
CGContextDrawImage( g, rect, imgRect );
CGImageRelease( imgRect );
CGImageRelease( imgAll );
and it's work fine for me
Related
In my iPad app, I have a UITableView that alloc/inits a UIView subclass every time a new cell is selected. I've overridden drawRect: in this UIView to draw a radial gradient and it works fine, but performance is suffering - when a cell is tapped, the UIView takes substantially longer to draw a gradient programmatically as opposed to using a .png for the background. Is there any way to "cache" my drawRect: method or the gradient it generates to improve performance? I'd rather use drawRect: instead of a .png. My method looks like this:
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
size_t gradLocationsNum = 2;
CGFloat gradLocations[2] = {0.0f, 1.0f};
CGFloat gradColors[8] = {0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.5f};
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace, gradColors, gradLocations, gradLocationsNum);
CGColorSpaceRelease(colorSpace);
CGPoint gradCenter = CGPointMake(CGRectGetMidX(self.bounds), CGRectGetMidY(self.bounds));
float gradRadius = MIN(self.bounds.size.width , self.bounds.size.height) ;
CGContextDrawRadialGradient (context, gradient, gradCenter, 0, gradCenter, gradRadius, kCGGradientDrawsAfterEndLocation);
CGGradientRelease(gradient);
}
Thanks!
You can render graphics into a context and then store that as a UIImage. This answer should get you started:
drawRect: is a method on UIView used to draw the view itself, not to pre-create graphic objects.
Since it seems that you want to create shapes to store them and draw later, it appears reasonable to create the shapes as UIImage and draw them using UIImageView. UIImage can be stored directly in an NSArray.
To create the images, do the following (on the main queue; not in drawRect:):
1) create a bitmap context
UIGraphicsBeginImageContextWithOptions(size, opaque, scale);
2) get the context
CGContextRef context = UIGraphicsGetCurrentContext();
3) draw whatever you need
4) export the context into an image
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
5) destroy the context
UIGraphicsEndImageContext();
6) store the reference to the image
[yourArray addObject:image];
Repeat for each shape you want to create.
For details see the documentation for the above mentioned functions. To get a better understanding of the difference between drawing in drawRect: and in arbitrary place in your program and of working with contexts in general, I would recommend you read the Quartz2D Programming Guide, especially the section on Graphics Contexts.
I have a png that I'm using as an image mask for another image. Both image have rounded corners that are being preserved with resizableImageWithCapInsets:. The image (not the mask) is being sized automatically because it is the progressImage of a UIProgressView.
The problem I'm having is that if I use CGImageMaskCreate to create a mask and simply give it the width of of the width of the UIProgressView, the mask image is being stretched (ie, it does not preserve the caps).
What I'd like to do is create a new UIImage with resizable caps, manually resize the image (perhaps by putting it in a UIImageView), get the data representation of the resized version of the mask image, then create a new image with that data and use that image as the mask. It seems, though, that even if I create a UIImageView with the image, and then set the frame of the UIImageView appropriately, getting the image back out of the view gives my original image.
Is there any way to get the result of a resizableImageWithCapInsets: image without it actually being drawn into the UI?
I would try drawing image piece by piece into CGContext where you can access data provider or extract NSData through creating UIImage
- (UIImage*) drawImage:(UIImage *)image
atSize:(CGSize) size
{
UIGraphicsBeginImageContext(size);
CGContextRef context = UIGraphicsGetCurrentContext();
[image drawInRect:CGRectMake(0, 0, size.width, size.height)];
CGImageRef cgImage = CGBitmapContextCreateImage(context);
UIImage *outImage = [UIImage imageWithCGImage:cgImage];
CGImageRelease(cgImage);
UIGraphicsEndImageContext();
return outImage;
}
I want to do some custom drawing with CoreGraphics. I need a linear gradient on my view, but the thing is that this view is a rounded rectangle so I want my gradient to be also rounded at angles. You can see what I want to achieve on the image below:
So is this possible to implement in CoreGraphics or some other programmatic and easy way?
Thank you.
I don't think there is an API for that, but you can get the same effect if you first draw a radial gradient, say, in an (N+1)x(N+1) size bitmap context, then convert the image from the context to a resizable image with left and right caps set to N.
Pseudocode:
UIGraphicsBeginImageContextWithOptions(CGSizeMake(N+1,N+1), NO, 0.0f);
CGContextRef context = UIGraphicsGetCurrentContext();
// <draw the gradient into 'context'>
UIImage* gradientBase = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIImage* gradientImage = [gradientBase resizableImageWithCapInsets:UIEdgeInsetsMake(0,N,0,N)];
In case you want the image to scale vertically as well, you just have to set the caps to UIEdgeInsetsMake(N,N,N,N).
I just want to add more sample code for this technique, as some things weren't obvious for. Maybe it will be useful for somebody:
So, let's say, we have our custom view class and in it's drawRect: method we put this:
// Defining the rect in which to draw
CGRect drawRect=self.bounds;
Float32 gradientSize=drawRect.size.height; // The size of original radial gradient
CGPoint center=CGPointMake(0.5f*gradientSize,0.5f*gradientSize); // Center of gradient
// Creating the gradient
Float32 colors[4]={0.f,1.f,1.f,0.2f}; // From opaque white to transparent black
CGGradientRef gradient=CGGradientCreateWithColorComponents(CGColorSpaceCreateDeviceGray(), colors, nil, 2);
// Starting image and drawing gradient into it
UIGraphicsBeginImageContextWithOptions(CGSizeMake(gradientSize, gradientSize), NO, 1.f);
CGContextRef context=UIGraphicsGetCurrentContext();
CGContextDrawRadialGradient(context, gradient, center, 0.f, center, center.x, 0); // Drawing gradient
UIImage* gradientImage=UIGraphicsGetImageFromCurrentImageContext(); // Retrieving image from context
UIGraphicsEndImageContext(); // Ending process
gradientImage=[gradientImage resizableImageWithCapInsets:UIEdgeInsetsMake(0.f, center.x-1.f, 0.f, center.x-1.f)]; // Leaving 2 pixels wide area in center which will be tiled to fill whole area
// Drawing image into view frame
[gradientImage drawInRect:drawRect];
That's all. Also if you're not going to ever change the gradient while app is running, you would want to put everything except last line in awakeFromNib method and then in drawRect: just draw the gradientImage into view's frame. Also don't forget to retain the gradientImage in this case.
I'm building an app like the photo app by apple in the iPad. I have large full-screen image and I show them using a scrollView for managing zooming and paging. The main problem happen when I try to create a grid with the thumbnail of the images. I create them as UIImageView overlapped on a UIButton. All works great, but when I try the app on the iPad, it requires a lot of memory, I suppose it depend on the rescaling of the Image. There's a way to create a UIImageView with the little image,rescaling the larger image, without using so much memory?
You can use UIGraphics to create a thumbnail. Here's this code to do it:
UIGraphicsBeginImageContext(CGSizeMake(length, length));
CGContextRef currentContext = UIGraphicsGetCurrentContext();
CGContextClipToRect( currentContext, clippedRect);
CGFloat scaleFactor = length/sideFull;
if (widthGreaterThanHeight) {
//a landscape image – make context shift the original image to the left when drawn into the context
CGContextTranslateCTM(currentContext, -((mainImage.size.width - sideFull) / 2) * scaleFactor, 0);
}
else {
//a portfolio image – make context shift the original image upwards when drawn into the context
CGContextTranslateCTM(currentContext, 0, -((mainImage.size.height - sideFull) / 2) * scaleFactor);
}
//this will automatically scale any CGImage down/up to the required thumbnail side (length) when the CGImage gets drawn into the context on the next line of code
CGContextScaleCTM(currentContext, scaleFactor, scaleFactor);
[mainImageView.layer renderInContext:currentContext];
UIImage* thumbnail = UIGraphicsGetImageFromCurrentImageContext();
I am trying to use an image (270 degrees of a circle, similar to a pacman logo, painted as Core Graphics) to create a mask. What I am doing is this
1. creating a Core Graphics path
CGContextSaveGState(context);
CGContextBeginPath(context);
CGContextMoveToPoint(context,circleCenter.x,circleCenter.y);
//CGContextSetAllowsAntialiasing(myBitmapContext, YES);
CGContextAddArc(context,circleCenter.x, circleCenter.y,circleRadius,startingAngle, endingAngle, 0); // 0 is counterclockwise
CGContextClosePath(context);
CGContextSetRGBStrokeColor(context,1.0,0.0,0.0,1.0);
CGContextSetRGBFillColor(context,1.0,0.0,0.0,0.2);
CGContextDrawPath(context, kCGPathFillStroke);
2. then I'm creating an image of the path that has the path just painted
CGImageRef pacmanImage = CGBitmapContextCreateImage (context);
3. restoring the context
CGContextRestoreGState(context);
CGContextSaveGState(context);
4. creating a 1 bit mask (which will provide the black-white mask)
bitsPerComponent = 1;
bitsPerPixel = bitsPerComponent * 1 ;
bytesPerRow = (CGImageGetWidth(imgToMaskRef) * bitsPerPixel);
mask = CGImageCreate(CGImageGetWidth(imgToMaskRef),
CGImageGetHeight(imgToMaskRef),
bitsPerComponent,
bitsPerPixel,
bytesPerRow,
greyColorSpace,
kCGImageAlphaNone,
CGImageGetDataProvider(pacmanImage),
NULL, //decode
YES, //shouldInterpolate
kCGRenderingIntentDefault);
5. masking the imgToMaskRef (which is a CGImageRef imgToMaskRef =imgToMask.CGImage;) with the mask just created
imageMaskedWithImage = CGImageCreateWithMask(imgToMaskRef, mask);
CGContextDrawImage(context,imgRectBox, imageMaskedWithImage);
CGImageRef maskedImageFinal = CGBitmapContextCreateImage (context);
6. returning the maskedImageFinal to the caller of this method (as wheelChoiceMadeState, which is a CGImageRef) who then updates the CALayer contents property with the image
theLayer.contents = (id) wheelChoiceMadeState;
the problem I am seeing is that the mask does not work properly and looks very strange indeed. I get strange patterns across the path painted by the Core Graphics. My hunch is there is something with CGImageGetDataProvider() but I am not sure.
Any help would be appreciated
thank you
CGImageGetDataProvider does not change the data at all. If the data of pacmanImage does not exactly match the parameters passed to CGImageCreate (bitsPer,bytesPer,colorSpace,...) the result is undefined. If it does exactly match, there would be no point in creating mask.
You need to create a grayscale CGBitmapContext to draw the mask into, and a CGImage that uses the same pixels and parameters as the bitmap. You can then use the CGImage to mask another image.
Only use CGBitmapContextCreateImage if you want a snapshot of a CGBitmapContext that you will continue to modify. For a single use bitmap, pass the same buffer to the bitmap and the matching CGImage you create.
Edit:
finalRect is the size the final image should be. It is either large enough to hold the original image, and the pacman is positioned inside it, or it is large enough to hold the pacman, and the original image is cropped to fit. In this example, the original image is cropped. Otherwise the pacman path would have to be positioned relative to the original image.
maskContext = CGBitmapContextCreate( ... , finalRect.size.width , finalRect.size.height , ... );
// add the pacman path and set the stroke and fill colors
CGContextDrawPath( maskContext , kCGPathFillStroke );
maskImage = CGBitmapContextCreateImage( maskContext );
imageToMask = CGImageCreateWithImageInRect( originalImage , finalRect );
finalImage = CGImageCreateWithMask( imageToMask , maskImage );