I have some UIViews that have different centers and transforms applied to them.
I want to reconstruct these views on to a bitmap context. (Basically I want to take what the user has created on screen and render it on to a movie file)
I am able to get the view rendered in the context to look almost correct however there seems to be an offset. I am thinking the problem is that the UIImageView's .center property is not reflected in the transforms that I am doing. However I am unsure how to do it.
Note that the UIViews are originally positioned/transformed relative to a 1024x768 ipad screen where as the video buffer is 352 x 288 pixels
If I just add a CGContextTranslateCTM(newContext,img.center.x,img.center.y) then everything looks completely off. Any ideas how to properly transform the view to the correct center?
CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
CGContextRotateCTM(newContext, M_PI_2);
CGContextScaleCTM(newContext, 1, -1);
for(int i=0; i<[self.renderObjects count]; i++){
UIImageView * img = [self.renderObjects objectAtIndex:i];
[img setNeedsDisplay];
[img setBackgroundColor:[UIColor colorWithRed:1 green:1 blue:1 alpha:0.2]];
CGContextSaveGState(newContext);
CGContextScaleCTM(newContext, 0.375, 0.34);
CGContextConcatCTM(newContext, img.transform);
[img.layer renderInContext:newContext];
CGContextRestoreGState(newContext);
}
Here is the code that made it work for me: note that the 1024, 768 is because the UIImageViews were positioned in the iPad coordinate system. The rotations are inverted though so if someone can find a general solution for that it would be great.
UIImageView * curr = your image
[curr setNeedsDisplay];
CGContextSaveGState(newContext);
CGContextScaleCTM(newContext,height/768.0,width/1024.0);
CGContextTranslateCTM(newContext, 768-curr.center.x, curr.center.y);
CGContextConcatCTM(newContext, curr.transform);
CGContextTranslateCTM(newContext, -curr.bounds.size.width/2, -curr.bounds.size.height/2);
[curr.layer renderInContext:newContext];
CGContextRestoreGState(newContext);
Related
I’m trying to make a custom UIProgressView where the image that gets filled up is the Nike Swoosh. I’ve tried to follow some tutorials but am getting nowhere.
My current approach:
Make the inside of swoosh transparent and surroundings black.
Then put a big UIProgressView behind that.
Since the middle of the swoosh is transparent, it looks like the swoosh is filling up.
But, modifying the height of the progress bar has proven to be a pain since it messes with the width in a weird way…and it’s hard to align the swoosh with the progress bar for responsiveness.
Are there any other ideas or libraries out there?
Thanks
My suggestion:
draw a second image programatically to apply as a mask against your 'swoosh' image, and then repeat this cyclically.
example, fill image from left (mask it from right)
{
//existing variables
IBOutlet UIImageView *swooshView;
}
-(UIImage *)maskImageOfSize:(CGSize )size filledTo:(CGFloat )percentage{
UIGraphicsBeginImageContextWithOptions ( size, NO, 0.0);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColourWithColour (context, [UIColor blackColor].CGColor);
CGRect fillRect = CGRectZero;
fillRect.size.height = size.height;
fillRect.size.width = size.width * percentage / 100.0;
fillRect.origin.x = (size.width - fillRect.size.width);
CGContextFillRect(context, fillRect);
UIImage *result = UIGraphicsGetImageFromImageContext();
UIGraphicsEndImageContext();
return result;
}
-(void)fillSwooshToPercentage:(CGFloat )percentage{
percentage = ((CGFloat ) fmaxf ( 0.0 , (fminf (100.0, (float) percentage ) ) );
// just policing a 'floor' and 'ceiling'...
swooshView.layer.mask = [self maskImageOfSize:self.swoosh.bounds.size filledTo:percentage];
}
I have a layer where I want the user to draw a 'mask' for cutting out images. It is semi-opaque so that they can see beneath what they are selecting.
How can I process this so that the drawing data has an alpha of 1.0, but retain the alpha channel (for masking)?
TL:DR - I'd like the black area to be a solid, single colour.
Here is the desired before and after (the white background should be transparent in both):
something like this:
for (pixel in image) {
if (pixel.alpha != 0.0) {
fill solid black
}
}
The following should do what you're after. Majority of the code is from How to set the opacity/alpha of a UIImage? I only added a test for the alpha value, before converting the colour of the pixel to black.
// Create a pixel buffer in an easy to use format
CGImageRef imageRef = [[UIImage imageNamed:#"testImage"] CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
UInt8 * m_PixelBuf = malloc(sizeof(UInt8) * height * width * 4);
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(m_PixelBuf, width, height,
bitsPerComponent, bytesPerRow, colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGContextRelease(context);
//alter the alpha when the alpha of the source != 0
int length = height * width * 4;
for (int i=0; i<length; i+=4) {
if (m_PixelBuf[i+3] != 0) {
m_PixelBuf[i+3] = 255;
}
}
//create a new image
CGContextRef ctx = CGBitmapContextCreate(m_PixelBuf, width, height,
bitsPerComponent, bytesPerRow, colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGImageRef newImgRef = CGBitmapContextCreateImage(ctx);
CGColorSpaceRelease(colorSpace);
CGContextRelease(ctx);
free(m_PixelBuf);
UIImage *finalImage = [UIImage imageWithCGImage:newImgRef];
CGImageRelease(newImgRef);
finalImage will now contain an image where all pixels that don't have an alpha of 0.0 have alpha of 1.
The underlying model for this app should not be images. This is not a question of "how do I create one rendition of the image from the other."
Instead, the underlying object model should be an array of paths. Then, when you want to create the image with translucent paths vs opaque paths, it's just a question of how you render this array of paths. Once you tackle it that way, the problem is not a complex image manipulation question but a simple rendering question.
By the way, I really like this array-of-paths model, because then it becomes quite trivial to do things like "gee, let me provide an undo function, letting the user remove one stroke at a time." It opens you up to all sorts of nice functional enhancements.
In terms of specifics of how to render these paths, it can be implemented in a variety of different ways. You could use custom drawRect function for UIView subclass that renders the paths with the appropriate alpha. Or you can do it with CAShapeLayer objects, too. Or you can do some hybrid (creating new image snapshots as you finish adding each path, saving you from having to re-render all of the paths each time). There are tons of ways of tackling this.
But the key insight is to employ an underlying model of an array of paths, and then the rendering of your two types of images becomes fairly trivial exercise:
The first image is a rendering of a bunch of paths as CAShapeLayer objects with alpha of 0.5. The second is the same rendering, but with an alpha of 1.0. Again, it doesn't matter if you use shape layers or low level Core Graphics calls, but the underlying idea is the same. Either render your paths with translucency or not.
In my project I have to make a screenshot of the screen and apply blur to create the effect of frosted glass. Content can be moved under the glass and blured picture changed.
I'v used Accelerate.framework to speedup blurring, also i,v used OpenGL to draw CIImage directly to GLView.
Now I'm looking for a way to optimize getting screenshot of the screen.
I use this method to get screenshot of some area at the bottom of the screen:
CGSize size = CGSizeMake(rect.size.width, rect.size.height);
// get screenshot of self.view
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGContextRef ctx = CGBitmapContextCreate(nil, size.width, size.height, 8, 0, colorSpaceRef, kCGImageAlphaPremultipliedFirst);
CGContextClearRect(ctx, rect);
CGColorSpaceRelease(colorSpaceRef);
CGContextSetInterpolationQuality(ctx, kCGInterpolationNone);
CGContextSetShouldAntialias(ctx, NO);
CGContextSetAllowsAntialiasing(ctx, NO);
CGContextTranslateCTM(ctx, 0.0, someView.frame.size.height);
CGContextScaleCTM(ctx, 1, -1);
//add mask
CGImageRef maskImage = [UIImage imageNamed:#"mask.png"].CGImage;
CGContextClipToMask(ctx, rect, maskImage);
[someView.layer renderInContext:ctx];
//get screenshot image
CGImageRef imageRef = CGBitmapContextCreateImage(ctx);
It works fine and fast if self.view has 1-2 subviews, but if there are several subviews (or it is tableview), then everything starts to slow down.
So i try to find a fast way to get pixels from some rect on screen. Maybe using a low-level API.
if just perform some animations , try this way , called -snapshotViewAfterScreenUpdates: or -resizableSnapshotViewFromRect:afterScreenUpdates:withCapInsets: method which are UIView provided , these method return UIView object without rendering into a bitmap image , so it is a more efficient .
On iOS and most mobile devices there is a restriction on the size of the image that you can load, due to memory contraints. Is it possible to have a large image on disk (say 5,000 pixels by 5,000 pixels) but only read a smaller rectangle within that image (say 100x100) into memory for display?
In other words, do you need to load the entire image into memory if you just want to see a small subsection of it? If it's possible to load just the smaller portion, how can we do this?
This way, one could save a lot of space like spritesheets do for repetitive content. It would be important to note that the overall goal is to minimize the file size so the large image should be compressed with jpeg or png or some other kind of compression. I suspect video formats are like this because you never load an entire video into the memory.
Although I have not utilized the techniques, you might find the following Apple Sample useful:
LargeImageDownsizing Sample
You could do something with mapped NSData like this:
UIImage *pixelDataForRect(NSString *fileName, const CGRect pixelRect)
{
// get the pixels from that image
uint32_t width = pixelRect.size.width;
uint32_t height = pixelRect.size.height;
// create the context
UIGraphicsBeginImageContext(CGSizeMake(width, height));
CGContextRef bitMapContext = UIGraphicsGetCurrentContext();
CGAffineTransform flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, height);
CGContextConcatCTM(bitMapContext, flipVertical);
// render the image (assume PNG compression)
CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef) [NSData dataWithContentsOfMappedFile:fileName]);
CGImageRef image = CGImageCreateWithPNGDataProvider(provider, NULL, YES, kCGRenderingIntentDefault);
CGDataProviderRelease(provider);
uint32_t imageWidth = CGImageGetWidth(image);
uint32_t imageHeight = CGImageGetHeight(image);
CGRect drawRect = CGRectMake(-pixelRect.origin.x, -((imageHeight - pixelRect.origin.y) - height), imageWidth, imageHeight);
CGContextDrawImage(bitMapContext, drawRect, image);
CGImageRelease(image);
UIImage *retImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return retImage;
}
Your best bet is using UIScrollView with CATiledLayer.
Check out the "Designing Apps with Scroll Views presentation from WWDC 2010 for a description of how to do this:
https://developer.apple.com/videos/wwdc/2010/
The idea is to take your large image and chop it down into tiles, and then use a UIScrollView to provide your user with a scrollable view of the image, only loading those sections of the image that are necessary based on the position of the scrollview. This is accomplished using CATiledLayer.
I've found some code which gives me a UIImage out of a PDF-File. It works, but I have two questions:
Is there a possibility to achieve a better quality of the UIImage? (See Screenshot)
I only see the first page in my UIImageView. Do I have to embed the file in a UIScrollView to be complete?
Or is it better to render just one page and use buttons to navigate through the pages?
P.S. I know that UIWebView can display PDF-Pages with some functionalities but I need it as a UIImage or at least in a UIView.
Bad quality Image:
Code:
-(UIImage *)image {
UIGraphicsBeginImageContext(CGSizeMake(280, 320));
CGContextRef context = UIGraphicsGetCurrentContext();
CFURLRef pdfURL = CFBundleCopyResourceURL(CFBundleGetMainBundle(), CFSTR("ls.pdf"), NULL, NULL);
CGPDFDocumentRef pdf = CGPDFDocumentCreateWithURL((CFURLRef)pdfURL);
CGContextTranslateCTM(context, 0.0, 320);
CGContextScaleCTM(context, 1.0, -1.0);
CGPDFPageRef page = CGPDFDocumentGetPage(pdf, 4);
CGContextSaveGState(context);
CGAffineTransform pdfTransform = CGPDFPageGetDrawingTransform(page, kCGPDFCropBox, CGRectMake(0, 0, 280, 320), 0, true);
CGContextConcatCTM(context, pdfTransform);
CGContextDrawPDFPage(context, page);
CGContextRestoreGState(context);
UIImage *resultingImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return resultingImage;
}
I know i'm a little late here, but i hope i can help someone else looking for an answer.
As to the questions asked:
I'm afraid the only way to achieve a better image quality is to render a bigger image, and letting the UIImageView resize it for you. I don't think you can set the resolution, but using a bigger image may be a good choice. It won't take too long for the page to render, and the image will have a better quality. PDF files are rendered on demand depending on the zoom level, that's why they seem to have "better quality".
As to rendering all the pages, you can get the number of pages in the document calling CGPDFDocumentGetNumberOfPages( pdf ) and using a simple for loop you can concat all the images generated in one single image. For displaying it, use the UIScrollVIew.
In my opinion, this approach is better than the above, but you should try to optimize it, for example rendering always the current, the previous and the next page. For nice scrolling transition effects, why not use a horizontal UIScrollView.
For more generic rendering code, i always do the rotation like this:
int rotation = CGPDFPageGetRotationAngle(page);
CGContextTranslateCTM(context, 0, imageSize.height);//moves up Height
CGContextScaleCTM(context, 1.0, -1.0);//flips horizontally down
CGContextRotateCTM(context, -rotation*M_PI/180);//rotates the pdf
CGRect placement = CGContextGetClipBoundingBox(context);//get the flip's placement
CGContextTranslateCTM(context, placement.origin.x, placement.origin.y);//moves the the correct place
//do all your drawings
CGContextDrawPDFPage(context, page);
//undo the rotations/scaling/translations
CGContextTranslateCTM(context, -placement.origin.x, -placement.origin.y);
CGContextRotateCTM(context, rotation*M_PI/180);
CGContextScaleCTM(context, 1.0, -1.0);
CGContextTranslateCTM(context, 0, -imageSize.height);
Steipete already mentioned setting the white background:
CGContextSetRGBFillColor(context, 1, 1, 1, 1);
CGContextFillRect(context, CGRectMake(0, 0, imageSize.width, imageSize.height));
So the last thing to keep in mind is when exporting an image, set the quality to the maximum. For example:
UIImageJPEGRepresentation(image, 1);
What are you doing with the CGContextTranslateCTM(context, 0.0, 320); call?
You should extract the proper metrics form the pdf, with code like this:
cropBox = CGPDFPageGetBoxRect(page, kCGPDFCropBox);
rotate = CGPDFPageGetRotationAngle(page);
Also, as you see, the pdf might has rotation info, so you need to use the CGContextTranslateCTM/CGContextRotateCTM/CGContextScaleCTM depending on the angle.
You also might wanna clip any content that is outside of the CropBox area, as pdf has various viewPorts that you usually don't wanna display (e.g. for printers so that seamless printing is possible) -> use CGContextClip.
Next, you're forgetting that the pdf reference defines a white background color. There are a lot of documents out there that don't define any background color at all - you'll get weird results if you don't draw a white background on your own --> CGContextSetRGBFillColor & CGContextFillRect.