I am Adding multiple CAShapeLayers to layer property of my UIView subclass by calling [self.layer addSublayer:shapeLayer];
To capture these layers in a UIImage I have implemented the following method which is meant to take an image of the layer property.
- (UIImage *)takeImage {
UIGraphicsBeginImageContext(self.frame.size);
CGContextRef context = UIGraphicsGetCurrentContext();
if (context) {
[self.layer renderInContext:context];
UIImage *snapshotImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return snapshotImage;
}
return nil;
}
My Problem is, that the resulting image is completely blank. Why is this so?
The image was great! Didn't set the IBOulet properly.
Related
I have a view that has a UIImage and a DrawView as subviews. The draw view responds to touches and creates a UIBezierPath for drawing on the image. When the user accepts their change I need to merge the underlying UIImage and any UIBezierPath's created into a single UIImage.
Make that UIBazierPath a public property of your DrawView, and keep updating it when user is drawing from within DrawView. When user hits the Accept button, use following code to simply Create a UIImageContext and draw both, the sourceImage and bezierPath over the context. Finally take whatever is drawn on the context in a resultImage.
UIBezierPath *path = drawView.Path // Your Bezier Path in DrawView
UIImage *sourceImage = sourceImageView.image; // Your Source Image from ImageView.
UIImage *resultImage = nil;
UIGraphicsBeginImageContext(sourceImage.size);
[sourceImage drawInRect:(CGRect){CGPointZero, sourceImage.size}];
[path stroke]; //Fill or Stroke path as you need.
[path fill];
resultImage = UIGraphicsGetImageFromCurrentImageContext(); //taking the merged result from context, in a new Image. This is your required image.
UIGraphicsEndImageContext();
//Use resultImage as you want.
I want to show an image in NSview or in the NSImageView. In my header file I have
#interface FVView : NSView
{
NSImageView *imageView;
}
#end
here is what I been trying to do in my implementation file:
- (void)drawRect:(NSRect)dirtyRect
{
[super drawRect:dirtyRect];
(Here I get an image called fitsImage........ then I do)
//Here I make the image
CGImageRef cgImage = CGImageRetain([fitsImage CGImageScaledToSize:maxSize]);
NSImage *imageR = [self imageFromCGImageRef:cgImage];
[imageR lockFocus];
//Here I have the view context
CGContextRef ctx = (CGContextRef)[[NSGraphicsContext currentContext] graphicsPort];
//Here I set the via dimensions
CGRect renderRect = CGRectMake(0., 0., maxSize.width, maxSize.height);
[self.layer renderInContext:ctx];
[imageR unlockFocus];
CGContextDrawImage(ctx, renderRect, cgImage);
CGImageRelease(cgImage);
}
I don't get anything in the NSview window when I run the script. No errors at all I just can't see what I'm doing wrong. My Xcode version in 5.1.1
I'm trying to learn how to manipulate CGImageRef and view it in a window or nsview.
Thank you.
I'm not quite sure what exactly your setup is. Drawing an image in a custom view is a separate thing from using an NSImageView. Also, a custom view that may (or may not) be layer-backed is different from a layer-hosting view.
You have a lot of the right elements, but they're all mixed up together. In no case do you have to lock focus on an NSImage. That's for drawing into an NSImage. Also, a custom view that subclasses from NSView doesn't have to call super in its -drawRect:. NSView doesn't draw anything.
To draw an image in a custom view, try:
- (void) drawRect:(NSRect)dirtyRect
{
CGImageRef cgImage = /* ... */;
NSSize maxSize = /* ... */;
CGContextRef ctx = (CGContextRef)[[NSGraphicsContext currentContext] graphicsPort];
CGRect renderRect = CGRectMake(0., 0., maxSize.width, maxSize.height);
CGContextDrawImage(ctx, renderRect, cgImage);
CGImageRelease(cgImage);
}
If you have an NSImageView, then you don't need a custom view or any drawing method or code. Just do the following at the point where you obtain the image or the information necessary to generate it:
NSImageView* imageView = /* ... */; // Often an outlet to a view in a NIB rather than a local variable.
CGImageRef cgImage = /* ... */;
NSImage* image = [[NSImage alloc] initWithCGImage:cgImage size:/* ... */];
imageView.image = image;
CGImageRelease(cgImage);
If you're working with a layer-hosting view, you just need to set the CGImage as the layer's content. Again, you do this whenever you obtain the image or the information necessary to generate it. It's not in -drawRect:.
CALayer* layer = /* ... */; // Perhaps someView.layer
CGImageRef cgImage = /* ... */;
layer.contents = (__bridge id)cgImage;
CGImageRelease(cgImage);
I'm trying to make a custom animation for replacing an NSView with another.
For that reason I need to get an image of the NSView before it appears on the screen.
The view may contain layers and NSOpenGLView subviews, and therefore standard options like initWithFocusedViewRect and bitmapImageRepForCachingDisplayInRect do not work well in this case (they layers or OpenGL content well in my experiments).
I am looking for something like CGWindowListCreateImage, that is able to "capture" an offline NSWindow including layers and OpenGL content.
Any suggestions?
I created a category for this:
#implementation NSView (PecuniaAdditions)
/**
* Returns an offscreen view containing all visual elements of this view for printing,
* including CALayer content. Useful only for views that are layer-backed.
*/
- (NSView*)printViewForLayerBackedView;
{
NSRect bounds = self.bounds;
int bitmapBytesPerRow = 4 * bounds.size.width;
CGColorSpaceRef colorSpace = CGColorSpaceCreateWithName(kCGColorSpaceSRGB);
CGContextRef context = CGBitmapContextCreate (NULL,
bounds.size.width,
bounds.size.height,
8,
bitmapBytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedLast);
CGColorSpaceRelease(colorSpace);
if (context == NULL)
{
NSLog(#"getPrintViewForLayerBackedView: Failed to create context.");
return nil;
}
[[self layer] renderInContext: context];
CGImageRef img = CGBitmapContextCreateImage(context);
NSImage* image = [[NSImage alloc] initWithCGImage: img size: bounds.size];
NSImageView* canvas = [[NSImageView alloc] initWithFrame: bounds];
[canvas setImage: image];
CFRelease(img);
CFRelease(context);
return canvas;
}
#end
This code is primarily for printing NSViews which contain layered child views. Might help you too.
Let me tell you about the problem I am having and how I tried to solve it. I have a UIScrollView which loads subviews as one scrolls from left to right. Each subview has 10-20 images around 400x200 each. When I scroll from view to view, I experience quite a bit of lag.
After investigating, I discovered that after unloading all the views and trying it again, the lag was gone. I figured that the synchronous caching of the images was the cause of the lag. So I created a subclass of UIImageView which loaded the images asynchronously. The loading code looks like the following (self.dispatchQueue returns a serial dispatch queue).
- (void)loadImageNamed:(NSString *)name {
dispatch_async(self.dispatchQueue, ^{
UIImage *image = [UIImage imageNamed:name];
dispatch_sync(dispatch_get_main_queue(), ^{
self.image = image;
});
});
}
However, after changing all of my UIImageViews to this subclass, I still experienced lag (I'm not sure if it was lessened or not). I boiled down the cause of the problem to self.image = image;. Why is this causing so much lag (but only on the first load)?
Please help me. =(
EDIT 3: iOS 15 now offers UIImage.prepareForDisplay(completionHandler:).
image.prepareForDisplay { decodedImage in
imageView.image = decodedImage
}
or
imageView.image = await image.byPreparingForDisplay()
EDIT 2: Here is a Swift version that contains a few improvements. (Untested.)
https://gist.github.com/fumoboy007/d869e66ad0466a9c246d
EDIT: Actually, I believe all that is necessary is the following. (Untested.)
- (void)loadImageNamed:(NSString *)name {
dispatch_async(self.dispatchQueue, ^{
// Determine path to image depending on scale of device's screen,
// fallback to 1x if 2x is not available
NSString *pathTo1xImage = [[NSBundle mainBundle] pathForResource:name ofType:#"png"];
NSString *pathTo2xImage = [[NSBundle mainBundle] pathForResource:[name stringByAppendingString:#"#2x"] ofType:#"png"];
NSString *pathToImage = ([UIScreen mainScreen].scale == 1 || !pathTo2xImage) ? pathTo1xImage : pathTo2xImage;
UIImage *image = [[UIImage alloc] initWithContentsOfFile:pathToImage];
// Decompress image
if (image) {
UIGraphicsBeginImageContextWithOptions(image.size, NO, image.scale);
[image drawAtPoint:CGPointZero];
image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}
// Configure the UI with pre-decompressed UIImage
dispatch_async(dispatch_get_main_queue(), ^{
self.image = image;
});
});
}
ORIGINAL ANSWER: It turns out that it wasn't self.image = image; directly. The UIImage image loading methods don't decompress and process the image data right away; they do it when the view refreshes its display. So the solution was to go a level lower to Core Graphics and decompress and process the image data myself. The new code looks like the following.
- (void)loadImageNamed:(NSString *)name {
dispatch_async(self.dispatchQueue, ^{
// Determine path to image depending on scale of device's screen,
// fallback to 1x if 2x is not available
NSString *pathTo1xImage = [[NSBundle mainBundle] pathForResource:name ofType:#"png"];
NSString *pathTo2xImage = [[NSBundle mainBundle] pathForResource:[name stringByAppendingString:#"#2x"] ofType:#"png"];
NSString *pathToImage = ([UIScreen mainScreen].scale == 1 || !pathTo2xImage) ? pathTo1xImage : pathTo2xImage;
UIImage *uiImage = nil;
if (pathToImage) {
// Load the image
CGDataProviderRef imageDataProvider = CGDataProviderCreateWithFilename([pathToImage fileSystemRepresentation]);
CGImageRef image = CGImageCreateWithPNGDataProvider(imageDataProvider, NULL, NO, kCGRenderingIntentDefault);
// Create a bitmap context from the image's specifications
// (Note: We need to specify kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little
// because PNGs are optimized by Xcode this way.)
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef bitmapContext = CGBitmapContextCreate(NULL, CGImageGetWidth(image), CGImageGetHeight(image), CGImageGetBitsPerComponent(image), CGImageGetWidth(image) * 4, colorSpace, kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little);
// Draw the image into the bitmap context
CGContextDrawImage(bitmapContext, CGRectMake(0, 0, CGImageGetWidth(image), CGImageGetHeight(image)), image);
// Extract the decompressed image
CGImageRef decompressedImage = CGBitmapContextCreateImage(bitmapContext);
// Create a UIImage
uiImage = [[UIImage alloc] initWithCGImage:decompressedImage];
// Release everything
CGImageRelease(decompressedImage);
CGContextRelease(bitmapContext);
CGColorSpaceRelease(colorSpace);
CGImageRelease(image);
CGDataProviderRelease(imageDataProvider);
}
// Configure the UI with pre-decompressed UIImage
dispatch_async(dispatch_get_main_queue(), ^{
self.image = uiImage;
});
});
}
I think, the problem could be Images themselves. For example - I got in one of my projects 10 images 640x600 layered with alpha transparency on each other. When I try to push or pop viewcontroller from this viewcontroller.. it lags a lot.
when I leave only few images or use quite smaller images - no lag.
P.S. tested on sdk 4.2 ios5 iphone 4.
I'd like to take a UITextView and allow the user to enter text into it and then trigger a copy of the contents onto a quartz bitmap context. Does anyone know how I can perform this copy action? Should I override the drawRect method and call [super drawRect] and then take the resulting context and copy it? If so, does anyone have any reference to sample code to copy from one context to another?
Update: from reading the link in the answer below, I put together this much to attempt to copy my UIView contents into a bitmap context, but something is still not right. I get my contents mirrored across the X axis (i.e. upside down). I tried using CGContextScaleCTM() but that seems to have no effect.
I've verified that the created UIImage from the first four lines do properly create a UIImage that isn't strangely rotated/flipped, so there is something I'm doing wrong with the later calls.
// copy contents to bitmap context
UIGraphicsBeginImageContext(mTextView.bounds.size);
[mTextView.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage* image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
[self setNeedsDisplay];
// render the created image to the bitmap context
CGImageRef cgImage = [image CGImage];
CGContextScaleCTM(mContext, 1.0, -1.0); // doesn't seem to change result
CGContextDrawImage(mContext, CGRectMake(
mTextView.frame.origin.x,
mTextView.frame.origin.y,
[image size].width, [image size].height), cgImage);
Any suggestions?
Here is the code I used to get a UIImage of UIView:
#implementation UIView (Sreenshot)
- (UIImage *)screenshot{
UIGraphicsBeginImageContextWithOptions(self.bounds.size, NO, [UIScreen mainScreen].scale);
/* iOS 7 */
BOOL visible = !self.hidden && self.superview;
CGFloat alpha = self.alpha;
BOOL animating = self.layer.animationKeys != nil;
BOOL success = YES;
if ([self respondsToSelector:#selector(drawViewHierarchyInRect:afterScreenUpdates:)]){
//only works when visible
if (!animating && alpha == 1 && visible) {
success = [self drawViewHierarchyInRect:self.bounds afterScreenUpdates:NO];
}else{
self.alpha = 1;
success = [self drawViewHierarchyInRect:self.bounds afterScreenUpdates:YES];
self.alpha = alpha;
}
}
if(!success){ /* iOS 6 */
self.alpha = 1;
[self.layer renderInContext:UIGraphicsGetCurrentContext()];
self.alpha = alpha;
}
UIImage* img = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return img;
}
#end
You can use in iOS 7 and later:
- (UIView *)snapshotViewAfterScreenUpdates:(BOOL)afterUpdates