It can be done by mallocing a temporary bitmap with 32bits per pixel
and then clearing the alpha component with a for loop and
and finally turn it back into a NSImage again.
I suspect is can be done in a simpler way using a clever
combination of NSColor and NSCompositingOperation. Or perhaps the image
needs to be composited with itself using drawAtPoint.
My code looks like this.
NSImage* img = some image with RGB and Alpha;
NSRect rect = some rect inside the image;
[img lockFocus];
[[NSColor clearColor] set];
NSRectFillUsingOperation(rect, NSCompositeXOR);
[img unlockFocus];
NOTE: Setting the alpha channel to 1 can be done by
using a blackColor with NSCompositePlusLighter.
What is the secret in clearing the alpha channel?
It won't be fast but this will work as well:
NSImage *newImage = [[NSImage alloc] initWithSize:[srcImage size]];
[newImage lockFocus];
[[NSColor whiteColor] set];
NSRectFill(NSMakeRect(0,0,[newImage size].width, [newImage size].height));
[srcImage compositeToPoint:NSZeroPoint operation:NSCompositeCopy];
[newImage unlockFocus];
Please read the AppKit release notes on the subject of image mutability. NSImage should basically be treated as immutable.
All of the pixel formats supported in graphics contexts have premultiplied alpha. If the alpha channel is zero, the other channels have to be zero too.
Related
I am trying to display a 32bit, 4 channeled image in my window. The fourth channel in the image is an alpha channel. As an experiment, I create a completely Red image, where each pixel has the RGB value: 255,0,0. For each pixel I also add an alpha value of 204.
What I expected to see was a completely Red image with some transparency, but what I see instead is a completely opaque image with the values altered.
Expected Output:
Current output:
The code I am using:
NSRect windowRect = {0,0,200,200};
m_NSWindow = [[NSWindow alloc] initWithContentRect:windowRect styleMask:NSBorderlessWindowMask backing:NSBackingStoreBuffered defer:NO];
[m_NSWindow setTitle:#"overlayWindow"];
[m_NSWindow makeKeyAndOrderFront:nil];
g_imageView = [[NSImageView alloc] initWithFrame:NSMakeRect(0,0,200,200)];
[m_NSWindow.contentView addSubview:g_imageView];
[m_NSWindow setOpaque:NO];
[m_NSWindow setAlphaValue:1.0];
NSBitmapImageRep* imageRep = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes:nil
pixelsWide:200
pixelsHigh:200
bitsPerSample:8
samplesPerPixel:4
hasAlpha:YES
isPlanar:NO
colorSpaceName:NSDeviceRGBColorSpace
bitmapFormat:NSAlphaNonpremultipliedBitmapFormat
bytesPerRow:(200*4)
bitsPerPixel:32];
memcpy(imageRep.bitmapData,m_paintBuffer.data,160000);
NSSize imageSize = NSMakeSize(200,200);
NSImage* myImage = [[NSImage alloc] initWithSize: imageSize];
[myImage addRepresentation:imageRep];
[g_imageView setImage:myImage];
where m_paintBuffer.data points to the raw pixel data for the image.
Not sure if it is relevant to the question, but m_paintBuffer is of type Mat from OpenCV
The window's content view is not the entirety of the window's content, as it were. Even a borderless window has (private) theme views surrounding and containing the content view.
In particular, the window has a background color of a light gray. This is drawn "behind" your content view and is opaque. However, you can change it by setting the window's backgroundColor property to, for example, [NSColor clearColor]. And that's what you should do to achieve your desired effect.
I have an NSImageView in the lower left with a red background. In the screenshot it is displaying a PDF document.
I want the shape of the document filled in white white, instead it is transparent and the red background bleeds through the document. How do I force the PDF to not be transparent?
Or the more general question, how do I get the NSImageView to fill transparent images with a solid color. My current strategy is to create a new image the same size with a white background and draw the original image on top and then use the new image in the image view. Is there a better way?
NSImage* newImage = [[NSImage alloc] initWithSize:[image size]];
[newImage lockFocus];
[[NSColor whiteColor] set];
CGRect rc = NSMakeRect(0,0,[newImage size].width, [newImage size].height);
NSRectFill(rc);
[image drawInRect:rc];
[newImage unlockFocus];
image = newImage;
I have an NSImage, initialized with PDF data, created like this:
NSData* data = [view dataWithPDFInsideRect:view.bounds];
slideImage = [[NSImage alloc] initWithData:data];
The slideImage is now the size of the view.
When I try to render the image in an NSImageView, it only draws sharp when the image view is exactly the original size of the image, even if you clear the cache or change the image size. I tried setting the cacheMode to NSImageCacheNever, which also didn't work. The only image rep in the image is the PDF one, and when I render it to a PDF file it shows that it's vector.
As a workaround, I create a NSBitmapImageRep with a different size, call drawInRect on the original image, and put the bitmap representation inside a new NSImage and render that, which works, but it feels like it's not optimal:
- (NSBitmapImageRep*)drawToBitmapOfWidth:(NSInteger)width
andHeight:(NSInteger)height
withScale:(CGFloat)scale
{
NSBitmapImageRep *bmpImageRep = [[NSBitmapImageRep alloc]
initWithBitmapDataPlanes:NULL
pixelsWide:width * scale
pixelsHigh:height * scale
bitsPerSample:8
samplesPerPixel:4
hasAlpha:YES
isPlanar:NO
colorSpaceName:NSCalibratedRGBColorSpace
bitmapFormat:NSAlphaFirstBitmapFormat
bytesPerRow:0
bitsPerPixel:0
];
bmpImageRep = [bmpImageRep bitmapImageRepByRetaggingWithColorSpace:
[NSColorSpace sRGBColorSpace]];
[bmpImageRep setSize:NSMakeSize(width, height)];
NSGraphicsContext *bitmapContext = [NSGraphicsContext graphicsContextWithBitmapImageRep:bmpImageRep];
[NSGraphicsContext saveGraphicsState];
[NSGraphicsContext setCurrentContext:bitmapContext];
[self drawInRect:NSMakeRect(0, 0, width, height) fromRect:NSZeroRect operation:NSCompositeCopy fraction:1];
[NSGraphicsContext restoreGraphicsState];
return bmpImageRep;
}
- (NSImage*)rasterizedImageForSize:(NSSize)size
{
NSImage* newImage = [[NSImage alloc] initWithSize:size];
NSBitmapImageRep* rep = [self drawToBitmapOfWidth:size.width andHeight:size.height withScale:1];
[newImage addRepresentation:rep];
return newImage;
}
How can I get the PDF to render nicely at any size without resorting to hacks like mine?
The point of NSImage is that you create it with the size (in points) that you want it to be. The backing representation can be vector based (e.g. PDF), and the NSImage is resolution independent (i.e. it supports different pixels per point), but the NSImage still has a fixed size (in points).
One one the points of an NSImage is that it will / can add a cache representation to speed up subsequent drawing.
If you need to draw a PDF to multiple sizes, and you want to use an NSImage, you're probably best of creating an NSImage for your given target size. If you want to, you can keep the NSPDFImageRef around -- I don't think it'll save you much.
We tried the following:
NSPDFImageRep* rep = self.representations.lastObject;
return [NSImage imageWithSize:size flipped:NO drawingHandler:^BOOL (NSRect dstRect)
{
[[NSGraphicsContext currentContext] setImageInterpolation:NSImageInterpolationHigh];
[rep drawInRect:dstRect fromRect:NSZeroRect operation:NSCompositeCopy fraction:1 respectFlipped:YES hints:#{
NSImageHintInterpolation: #(NSImageInterpolationHigh)
}];
return YES;
}];
And that does give you nice results when scaling up, but makes for blurry images
when scaling down.
I am working on a OSX/Cocoa graphics application which (for performance reasons) I would like to render at 640x480 when the user selects "full screen" mode. For what it's worth, the content is a custom NSView which draws using openGL.
I understand that rather than actually change the user's resolution, it's preferable to change the backbuffer (as explained on another SO question here: Programmatically change resolution OS X).
Following that advice, I end up with the following two methods (see below) to toggle between fullscreen and windowed. The trouble is that when I go fullscreen, the content does indeed render at 640x480 but is not scaled (IE it appears as if we stayed at the window's resolution and "zoomed" into a 640x480 corner of the render).
I'm probably missing something obvious here - I suppose I could translate the render according to the actual screen resolution to "center" it, but that seems overcomplicated?
- (void)goFullscreen{
// Bounce if we're already fullscreen
if(_isFullscreen){return;}
// Save original size and position
NSRect frame = [self.window.contentView frame];
original_size = frame.size;
original_position = frame.origin;
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:NO],NSFullScreenModeAllScreens,
nil];
// In lieu of changing resolution, we set the backbuffer to 640x480
GLint dim[2] = {640, 480};
CGLSetParameter([[self openGLContext] CGLContextObj], kCGLCPSurfaceBackingSize, dim);
CGLEnable ([[self openGLContext] CGLContextObj], kCGLCESurfaceBackingSize);
// Go fullscreen!
[self enterFullScreenMode:[NSScreen mainScreen] withOptions:options];
_isFullscreen=true;
}
- (void)goWindowed{
// Bounce if we're already windowed
if(!_isFullscreen){return;}
// Reset backbuffer
GLint dim[2] = {original_size.width, original_size.height};
CGLSetParameter([[self openGLContext] CGLContextObj], kCGLCPSurfaceBackingSize, dim);
CGLEnable ([[self openGLContext] CGLContextObj], kCGLCESurfaceBackingSize);
// Go windowed!
[self exitFullScreenModeWithOptions:nil];
[self.window makeFirstResponder:self];
_isFullscreen=false;
}
Update
Here's now to do something similar to datenwolf's suggestion below, but not using openGL (useful for non-gl content).
// Render into a specific size
renderDimensions = NSMakeSize(640, 480);
NSImage *drawIntoImage = [[NSImage alloc] initWithSize:renderDimensions];
[drawIntoImage lockFocus];
[self drawViewOfSize:renderDimensions];
[drawIntoImage unlockFocus];
[self syphonSendImage:drawIntoImage];
// Resize to fit preview area and draw
NSSize newSize = NSMakeSize(self.frame.size.width, self.frame.size.height);
[drawIntoImage setSize: newSize];
[[NSColor blackColor] set];
[self lockFocus];
[NSBezierPath fillRect:self.frame];
[drawIntoImage drawAtPoint:NSZeroPoint fromRect:self.frame operation:NSCompositeCopy fraction:1];
[self unlockFocus];
Use a FBO with a texture of the desired target resolution attached and render to that FBO/texture in said resolution. Then switch to the main framebuffer and draw a full screen quad using the texture rendered to just before. Use whatever magnification filter you like best. If you want to bring out the big guns you could implement a Lancosz / sinc interpolator in the fragment shader to upscaling the intermediary texture.
I have an NSAttributedString which I would like to draw into a CGImage so that I can later draw the CGImage into an NSView. Here's what I have so far:
// Draw attributed string into NSImage
NSImage* cacheImage = [[NSImage alloc] initWithSize:NSMakeSize(w, h)];
[cacheImage lockFocus];
[attributedString drawWithRect:NSMakeRect(0, 0, width, height) options:0];
[cacheImage unlockFocus];
// Convert NSImage to CGImageRef
CGImageSourceRef source = CGImageSourceCreateWithData(
(CFDataRef)[cacheImage TIFFRepresentation], NULL);
CGImageRef img = CGImageSourceCreateImageAtIndex(source, 0, NULL);
I'm not using -[NSImage CGImageForProposedRect:context:hints] because my app must use the 10.5 sdk.
When I draw this into my NSView using CGContextDrawImage, it draws a transparent background around the text, causing whatever is behind the window to show through. I think I want to create a clipping mask, but I can't figure out how to do that.
It sounds like your blend mode it set up as Copy instead of SourceOver. Take a look at the CoreGraphics blend mode documentation.