I am drawing a Linear Gradient on one of my CALayers with some colors, but randomly, with the same input, the colors are drawn on the screen as a pink color.
The code is as follows:
bottomComponents = bottomColor.colorComponents;
topComponents = topColor.colorComponents;
middleComponents = middleColor.colorComponents;
CGContextRef currentContext = UIGraphicsGetCurrentContext();
CGGradientRef glossGradient;
CGColorSpaceRef rgbColorspace;
size_t numberOfLocations = 3;
CGFloat locations[3] = {0.0f, MIDDLE_POINT, 1.0f};
CGFloat components[12] =
{
topComponents.red, topComponents.green, topComponents.blue, topComponents.alpha,
middleComponents.red, middleComponents.green, middleComponents.blue, middleComponents.alpha,
bottomComponents.red, bottomComponents.green, bottomComponents.blue, bottomComponents.alpha
};
rgbColorspace = CGColorSpaceCreateDeviceRGB();
glossGradient = CGGradientCreateWithColorComponents(rgbColorspace, components, locations, numberOfLocations);
CGRect currentBounds = self.bounds;
CGPoint topCenter = CGPointMake(CGRectGetMidX(currentBounds), 0.0f);
CGPoint bottomCenter = CGPointMake(CGRectGetMidX(currentBounds), CGRectGetHeight(currentBounds));
CGContextDrawLinearGradient(currentContext, glossGradient, topCenter, bottomCenter, 0);
CGGradientRelease(glossGradient);
CGColorSpaceRelease(rgbColorspace);
Where colorComponents is just returning a struct with the color components.
When I output the color in a log, it is the proper color, but when it shows up on screen, regardless of the start colors, it is a pink-ish color.
Is there anything that I have done wrong that could cause the random pink to show up?
The pink shows up completely sporadically. I will load from the exact same values and rarely, but surely, it will show up pink. Loading from different values yields the same results. Its happening around 1-2% of the time.
Any chance some of the times you use UIColor predefined colors? (For example greenColor)
I found those don't generate proper components.
Liviu
Related
I have an app that renders into a UIView's CGContext in drawRect. I also export those renderings using a background renderer. It uses the same rendering logic to render (in faster than real time) into a CGBitmapContext (which I subsequently transform into an mp4 file).
I have noticed that the output video has a number of weird glitches. Such as the image being rotated, weird duplications of the rendered images, random noise, and the timing is also odd.
I'm looking for ways to debug this. For the timing issue, I thought I'd render a string that tells me which frame I'm currently viewing, only to find rendering text into CGContext's not very well documented. In fact, the documentations around much of core graphics is quite unforgiving to some one of my experience.
So specifically, I'd like to know how to render text into a context. If its Core Text, must it inter-operate some how with the core graphics context? And in general, I'd appreciate any tips and advice on doing bitmap rendering and debugging the results.
according another question:
How to convert Text to Image in Cocoa Objective-C
we can use the CTLineDraw to draw the text in a CGBitmapContext
sample code:
NSString* string = #"terry.wang";
CGFloat fontSize = 10.0f;
// Create an attributed string with string and font information
CTFontRef font = CTFontCreateWithName(CFSTR("Helvetica Light"), fontSize, nil);
NSDictionary* attributes = [NSDictionary dictionaryWithObjectsAndKeys:
(id)font, kCTFontAttributeName,
nil];
NSAttributedString* as = [[NSAttributedString alloc] initWithString:string attributes:attributes];
CFRelease(font);
// Figure out how big an image we need
CTLineRef line = CTLineCreateWithAttributedString((CFAttributedStringRef)as);
CGFloat ascent, descent, leading;
double fWidth = CTLineGetTypographicBounds(line, &ascent, &descent, &leading);
// On iOS 4.0 and Mac OS X v10.6 you can pass null for data
size_t width = (size_t)ceilf(fWidth);
size_t height = (size_t)ceilf(ascent + descent);
void* data = malloc(width*height*4);
// Create the context and fill it with white background
CGColorSpaceRef space = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGImageAlphaPremultipliedLast;
CGContextRef ctx = CGBitmapContextCreate(data, width, height, 8, width*4, space, bitmapInfo);
CGColorSpaceRelease(space);
CGContextSetRGBFillColor(ctx, 1.0, 1.0, 1.0, 1.0); // white background
CGContextFillRect(ctx, CGRectMake(0.0, 0.0, width, height));
// Draw the text
CGFloat x = 0.0;
CGFloat y = descent;
CGContextSetTextPosition(ctx, x, y);
CTLineDraw(line, ctx);
CFRelease(line);
I want to make a graph in a UIView that shows numerical data. So I need to draw axis, a few coordinate lines, some tick marks, and then the data as connected straight lines. The data might typically consist of a few hundred x values in the range -500. to +1000. with corresponding y values in the range 300. to 350.
So I thought a good approach would be to transform the coordinates of the UIView so (for the example values given) the left side of the view is -500, and right side is 1000, the top is 400 and the bottom is 300. And y increases upwards. Then in drawRect: I could write a bunch of CGContextMoveToPoint() and CGContextAddLineToPoint() statements with my own coordinate system and not have to mentally translate each call to the UIView coordinates.
I wrote the following function to generate my own CGContextRef but it doesn't do what I expected. I've been trying variations on it for a couple days now and wasting so much time. Can someone say how to fix it? I realize I can't get clear in my mind whether the transform is supposed to specify the UIView coordinates in terms of my coordinates, or vice versa, or something else entirely.
static inline CGContextRef myCTX(CGRect rect, CGFloat xLeft, CGFloat xRight, CGFloat yBottom, CGFloat yTop) {
CGAffineTransform ctxTranslate = CGAffineTransformMakeTranslation(xLeft, rect.size.height - yTop);
CGAffineTransform ctxScale = CGAffineTransformMakeScale( rect.size.width / (xRight - xLeft), -rect.size.height / (yTop - yBottom) ); //minus so y increases toward top
CGAffineTransform combinedTransform = CGAffineTransformConcat(ctxTranslate, ctxScale);
CGContextRef c = UIGraphicsGetCurrentContext();
CGContextConcatCTM(c, combinedTransform);
return c;
}
The way I'm using this is that inside drawRect I just have:
CGContextRef ctx = myCTX(rect, self.xLeft, self.xRight, self.yBottom, self.yTop);
and then a series of statements like:
CGContextAddLineToPoint(ctx, [x[i] floatValue], [y[i] floatValue]);
I figured this out by experimenting. The transform requires 3 steps instead of 2 (or, if not required, at least it works this way):
static inline CGContextRef myCTX(CGRect rect, CGFloat xLeft, CGFloat xRight, CGFloat yBottom, CGFloat yTop) {
CGAffineTransform translate1 = CGAffineTransformMakeTranslation(-xLeft, -yBottom);
CGAffineTransform scale = CGAffineTransformMakeScale( rect.size.width / (xRight - xLeft), -rect.size.height / (yTop - yBottom) );
CGAffineTransform transform = CGAffineTransformConcat(translate1, scale);
CGAffineTransform translate2 = CGAffineTransformMakeTranslation(1, rect.size.height);
transform = CGAffineTransformConcat(transform, translate2);
CGContextRef c = UIGraphicsGetCurrentContext();
CGContextConcatCTM(c, transform);
return c;
}
You use this function inside drawRect. In my case the xLeft, xRight, etc. values are properties of a UIView subclass and are set by the viewController. So the view's drawRect looks like so:
- (void)drawRect:(CGRect)rect
{
CGContextRef c = UIGraphicsGetCurrentContext();
CGContextSaveGState(c);
CGContextRef ctx = myCTX(rect, self.xLeft, self.xRight, self.yBottom, self.yTop);
…
all of the CGContextMoveToPoint(), CGContextAddLineToPoint(), calls to
draw your desired lines, rectangles, curves, etc. but not stroke or fill them
…
CGContextRestoreGState(c);
CGContextSetLineWidth(c, 1);
CGContextStrokePath(c);
}
The CGContextSetLineWidth call isn't needed if you want a line width of 1. If you don't restore the graphics state before strokePath the path width is affected by the scaling.
Now I have to figure out how to draw text onto the view.
My end goal is to fill an arbitrarily sized rectangle with an NSImage. I want to:
Fill the entire rectangle
Preserve the aspect ratio of the image
Show as much as possible of the image while maintaining 1) and 2)
When not all the image can be shown, crop toward the center.
This demonstrates what I'm trying to do. The original image of the boat at the top is drawn into various sized rectangles below.
Okay, so far so good. I added a category to NSImage to do this.
#implementation NSImage (Fill)
/**
* Crops source to best fit the destination
*
* destRect is the rect in which we want to draw the image
* sourceRect is the rect of the image
*/
-(NSRect)scaleAspectFillRect:(NSRect)destRect fromRect:(NSRect)sourceRect
{
NSSize sourceSize = sourceRect.size;
NSSize destSize = destRect.size;
CGFloat sourceAspect = sourceSize.width / sourceSize.height;
CGFloat destAspect = destSize.width / destSize.height;
NSRect cropRect = NSZeroRect;
if (sourceAspect > destAspect) { // source is proportionally wider than dest
cropRect.size.height = sourceSize.height;
cropRect.size.width = cropRect.size.height * destAspect;
cropRect.origin.x = (sourceSize.width - cropRect.size.width) / 2;
} else { // dest is proportionally wider than source (or they are equal)
cropRect.size.width = sourceSize.width;
cropRect.size.height = cropRect.size.width / destAspect;
cropRect.origin.y = (sourceSize.height - cropRect.size.height) / 2;
}
return cropRect;
}
- (void)drawScaledAspectFilledInRect:(NSRect)rect
{
NSRect imageRect = NSMakeRect(0, 0, [self size].width, [self size].height);
NSRect sourceRect = [self scaleAspectFillRect:rect fromRect:imageRect];
[[NSGraphicsContext currentContext]
setImageInterpolation:NSImageInterpolationHigh];
[self drawInRect:rect
fromRect:sourceRect
operation:NSCompositeSourceOver
fraction:1.0 respectFlipped:YES hints:nil];
}
#end
When I want to draw the image into a certain rectangle I call:
[myImage drawScaledAspectFilledInRect:onScreenRect];
Works really well except for one problem. At certain sizes the image looks quite blurry:
My first thought was that I need to draw on integral pixels, so I used NSIntegralRect() before drawing. No luck.
As I thought about it I figured that it's probably a result of the interpolation. To draw from the larger image to the smaller draw rect NSImage has to interpolate. The blurry images are likely just a case where the values don't map very well and we end up with some undesirable artifacts that can't be avoided.
So, the question is this: How do I choose an optimal rect that avoids those artifacts? I can adjust either the draw rect or the crop rect before drawing to avoid this, but I don't know how or when to adjust them.
I'm trying to emulate the color tint effect from the UITabBarItem.
When I draw a linear gradient at an angle, I get visible aliasing in the middle part of the gradient where the two colors meet at the same location. Left is UITabBarItem, right is my gradient with visible aliasing (stepping):
Here is the snippet of relevant code:
UIGraphicsBeginImageContextWithOptions(size, NO, 0.0);
CGContextRef c = UIGraphicsGetCurrentContext();
CGContextSaveGState(c);
CGContextScaleCTM(c, 1.0, -1.0);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGFloat components[16] = {1,1,1,1,
109.0/255.0,175.0/255.0,246.0/255.0,1,
31.0/255.0,133.0/255.0,242.0/255.0,1,
143.0/255.0,194.0/255.0,248.0/255.0,1};
CGFloat locations[4] = {0.0, 0.62, 0.62, 1};
CGGradientRef colorGradient =
CGGradientCreateWithColorComponents(colorSpace, components,
locations, (size_t)4);
CGContextDrawLinearGradient(c, colorGradient, CGPointZero,
CGPointMake(size.width*1.0/3.9, -size.height),0);
CGGradientRelease(colorGradient);
CGColorSpaceRelease(colorSpace);
CGContextRestoreGState(c);
UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return resultImage;
What do I need to change, to get a smooth angled gradient like in UITabBarItem?
What is the interpolation quality of your context set to? CGContextGetInterpolationQuality()/CGContextSetInterpolationQuality(). Try changing that if it's too low.
If that doesn't work, I'm curious what happens if you draw the gradient vertically (0,Ymin)-(0,Ymax) but apply a rotation transformation to your context...
As a current workaround, I draw the gradient at double resolution into an image and then draw the image with original dimensions. The image scaling that occurs, takes care of the aliasing. At the pixel level the result is not as smooth as in the UITabBarItem, but that probably uses an image created in Photoshop or something similar.
I've finally got my main app release (Tap Play MMO - check it out ;-) ) and I'm now working on expanding it.
To do this I need to have a circle that has four seperate buttons in it, these buttons will essentially be quarters. I've come to the conclusion that the circlular image will need to be constructed of four images, one for each quarter, but due to the necessity of rectangular image shapes I'm going to end up with some overlap, although the overlap will be transparent.
What's the best way of getting this to work? I need something really simple really, I've looked at this
http://iphonedevelopment.blogspot.com/2010/03/irregularly-shaped-uibuttons.html
Before but not yet succeeded in getting it to work. Anyone able to offer some advice?
In case it makes any difference I'll be deploying to a iOS 3.X framework (will be 4.2 down the line when 4.2 comes out for iPad)
Skip the buttons and simply respond to touches in your view that contains the circle.
Create a CGPath for each area that you want to capture touches, when your UIview receives a touch, check for membership inside the paths.
[Edited answer to show skeleton implementation details -- TomH]
Here's how I would approach the problem: (I haven't tested this code and the syntax may not be quite right, but this is the general idea)
1) Using PS or your favorite image creation application, create one png of the quarter circles. Add it to your XCode project.
2) Add a UIView to the UI. Set the UIView's layer's contents to the png.
self.myView = [[UIView alloc] initWithRect:CGRectMake(10.0, 10.0, 100.0, 100,0)];
[myView.layer setContents:(id)[UIImage loadImageNamed:#"my.png"]];
3) Create CGPaths that describe the region in the UIView that you are interested in.
self.quadrantOnePath = CGPathCreateMutable();
CGPathMoveToPoint(self.quadrantOnePath, NULL, 50.0, 50.0);
CGPathAddLineToPoint(self.quadrantOnePath, NULL, 100.0, 50.0);
CGPathAddArc(self.quadrantOnePath, NULL, 50.0, 50.0, 50.0, 0.0, M_PI2, 1);
CGPathCloseSubpath(self.quadrantOnePath);
// create paths for the other 3 circle quadrants too!
4) Add a UIGestureRecognizer and listen/observe for taps in the view
UITapGestureRecognizer *tapRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(handleGesture:)];
[tapRecognizer setNumberOfTapsRequired:2]; // default is 1
5) When tapRecognizer invokes its target selector
- (void)handleGesture:(UIGestureRecognizer *) recognizer {
CGPoint touchPoint = [recognizer locationOfTouch:0 inView:self.myView];
bool processTouch = CGPathContainsPoint(self.quadrantOnePath, NULL, touchPoint, true);
if(processTouch) {
// call your method to process the touch
}
}
Don't forget to release everything when appropriate -- use CGPathRelease to release paths.
Another thought: If the graphic that you are using to represent your circle quadrants is simply a filled color (i.e. no fancy graphics, layer effects, etc.), you could also use the paths you created in the UIView's drawRect method to draw the quadrants too. This would address one of the failings of the approach above: there isn't a tight integration between the graphic and the paths used to check for the touches. That is, if you swap out the graphic for something different, change the size of the graphic, etc., your paths used to check for touches will be out of sync. Potentially a high maintenance piece of code.
I can't see, why overlapping is needed.
Just create 4 buttons and give each one a slice of your image.
edit after comment
see this great project. One example is exactly what you want to do.
It works by incorporating the alpha-value of a pixel in the overwritten
pointInside:withEvent: and a category on UIImage, that adds this method
- (UIColor *)colorAtPixel:(CGPoint)point {
// Cancel if point is outside image coordinates
if (!CGRectContainsPoint(CGRectMake(0.0f, 0.0f, self.size.width, self.size.height), point)) {
return nil;
}
// Create a 1x1 pixel byte array and bitmap context to draw the pixel into.
// Reference: http://stackoverflow.com/questions/1042830/retrieving-a-pixel-alpha-value-for-a-uiimage
NSInteger pointX = trunc(point.x);
NSInteger pointY = trunc(point.y);
CGImageRef cgImage = self.CGImage;
NSUInteger width = self.size.width;
NSUInteger height = self.size.height;
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
int bytesPerPixel = 4;
int bytesPerRow = bytesPerPixel * 1;
NSUInteger bitsPerComponent = 8;
unsigned char pixelData[4] = { 0, 0, 0, 0 };
CGContextRef context = CGBitmapContextCreate(pixelData,
1,
1,
bitsPerComponent,
bytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextSetBlendMode(context, kCGBlendModeCopy);
// Draw the pixel we are interested in onto the bitmap context
CGContextTranslateCTM(context, -pointX, pointY-(CGFloat)height);
CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, (CGFloat)width, (CGFloat)height), cgImage);
CGContextRelease(context);
// Convert color values [0..255] to floats [0.0..1.0]
CGFloat red = (CGFloat)pixelData[0] / 255.0f;
CGFloat green = (CGFloat)pixelData[1] / 255.0f;
CGFloat blue = (CGFloat)pixelData[2] / 255.0f;
CGFloat alpha = (CGFloat)pixelData[3] / 255.0f;
return [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
}
Here's an awesome project that solves the problem of irregular shaped buttons so easily:
http://christinemorris.com/2011/06/ios-irregular-shaped-buttons/