I have a custom view with that code :
- (void)drawRect:(CGRect)rect
{
UIImage* theImage = [UIImage imageNamed:#"blue_arrow"];
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetStrokeColorWithColor(context, [UIColor whiteColor].CGColor);
CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);
CGContextSetLineWidth(context, 1.0);
CGContextSetTextDrawingMode(context, kCGTextFill);
CGPoint posOnScreen = self.center;
CGContextDrawImage(context, CGRectMake(posOnScreen.x - theImage.size.width/2,
posOnScreen.y - theImage.size.height/2,
theImage.size.width,
theImage.size.height),
theImage .CGImage);
}
The image is an arrow, pointiing to the top.
But when drawn, it is draw upside down, pointing to bottom.
What causes that problem ?
How may I correct that, naturally without side effect ?
This is because Core Graphics is using a flipped coordinate system.
You could try flipping the object you're drawing to using the isFlipped property.
Or you could try using this code in your drawing method (Source):
CGContextTranslateCTM(context, 0, image.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
Related
I am creating a drawing app. One of the features is multicolour line drawing. It should work like user touch up the screen and leads on it drawing a line. Colour of the line changes smoothly. Like that http://www.examples.pavelgatilov.com/Screen%20Shot%202013-09-22%20at%208.37.42%20PM.png
I tried several approaches, but haven't been lucky.
My line drawing method is below:
- (void) drawLineFrom:(CGPoint)from to:(CGPoint)to width:(CGFloat)width
{
self.drawColor = toolColor;
UIGraphicsBeginImageContext(self.frame.size);
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextScaleCTM(ctx, 1.0f, -1.0f);
CGContextTranslateCTM(ctx, 0.0f, -self.frame.size.height);
if (drawImage != nil) {
CGRect rect = CGRectMake(0.0f, 0.0f, self.frame.size.width, self.frame.size.height);
CGContextDrawImage(ctx, rect, drawImage.CGImage);
}
CGContextSetLineCap(ctx, kCGLineCapRound);
CGContextSetLineWidth(ctx, width);
CGContextSetStrokeColorWithColor(ctx, self.drawColor.CGColor);
CGContextMoveToPoint(ctx, from.x, from.y);
CGContextAddLineToPoint(ctx, to.x, to.y);
CGContextStrokePath(ctx);
CGContextFlush(ctx);
drawImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
drawLayer.contents = (id)drawImage.CGImage;
}
Thanks for your help
Depending on exactly what colours, how they change and what effect you want / what happens with turns in the line, you may want to look at some combination of:
CGContextDrawLinearGradient with masking to the users drawn path.
colorWithPatternImage:
CGContextDrawLinearGradient drawn behind another layer and drawing transparency into the top layer with kCGBlendModeClear
How to draw a line on the UIImageView? I am using the UIImageView Sub Class, Its not support drawRect: method. I want to draw a line on the image view. How can I do this? Please help me. I am using below code for draw line.
- (void)drawRect:(CGRect)rect {
CGContextRef c = UIGraphicsGetCurrentContext();
CGFloat red[4] = {1.0f, 0.0f, 0.0f, 1.0f};
CGContextSetStrokeColor(c, red);
CGContextBeginPath(c);
CGContextMoveToPoint(c, 5.0f, 5.0f);
CGContextAddLineToPoint(c, 50.0f, 50.0f);
CGContextStrokePath(c);
}
The following code works by creating a new image the same size as the original, drawing a copy of the original image onto the new image, then drawing a 1 pixel line along to the top of the new image.
// UIImage *originalImage = <the image you want to add a line to>
// UIColor *lineColor = <the color of the line>
UIGraphicsBeginImageContext(originalImage.size);
// Pass 1: Draw the original image as the background
[originalImage drawAtPoint:CGPointMake(0,0)];
// Pass 2: Draw the line on top of original image
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 1.0);
CGContextMoveToPoint(context, 0, 0);
CGContextAddLineToPoint(context, originalImage.size.width, 0);
CGContextSetStrokeColorWithColor(context, [lineColor CGColor]);
CGContextStrokePath(context);
// Create new image
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
// Tidy up
UIGraphicsEndImageContext();
First, I wouldn't use a UIImageView. In fact the docs say...
If your subclass needs custom drawing code, it is recommended you use
UIView as the base class.
Use a UIView.
In the UIView add a UIImageView subView and put the image in there. Now you can do you custom drawing in the drawRect method of the UIView and it will appear on top of the image.
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor);
CGContextSetLineWidth(context, 5.0);
CGContextStrokeRect(context, self.bounds);
}
If this isn't working then the drawRect method probably isn't being called. Set a breakpoint to test it.
The best way to go about it in my opinion would be to take a invisible UIView of the same size as UIImageView for drawing and implement the touch methods on the UIView for drawing.
you can use something like:
CGPoint temp=[touch locationInView:self];
Use this in methods like:
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event;
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
Store all the points in an array and then draw those points on the UIImageView as it is.
Refer to Muhammad Saad Ansari
With Swift
func drawLines ( originalImage:UIImage, lineColor:CGColor ) -> UIImage{
UIGraphicsBeginImageContextWithOptions(originalImage.size,false,0.0)
originalImage.drawInRect(CGRectMake( 0, 0, originalImage.size.width, originalImage.size.height ))
let context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 5.0);
CGContextMoveToPoint(context, 0, 0);
CGContextAddLineToPoint(context, originalImage.size.width, 0);
CGContextSetStrokeColorWithColor(context,lineColor);
CGContextStrokePath(context);
// Create new image
var newImage = UIGraphicsGetImageFromCurrentImageContext();
// Tidy up
UIGraphicsEndImageContext();
return newImage
}
I am creating a simple drawing application in which I have a UIView in background & UIImageView in foreground. I am doing some drawing stuff in UIView and I have set an image in UIImageView. I want to add the transparency effect in UIImageView to show the lines behind the image. I know I can do this by reducing alpha, but I don’t want to change the alpha of image.
I want to do it with CGContextSetBlendMode, but I don’t know how to do this. Kindly help me to resolve this issue.
Thanks!
IMAGE http://www.freeimagehosting.net/q3237
UIImage *img = [UIImage imageNamed:#"Image.png"];
UIGraphicsBeginImageContext(self.view.frame.size);
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetBlendMode(ctx, kCGBlendModeMultiply);
[img drawInRect:CGRectMake(0, 0, 768, 1004) blendMode:kCGBlendModeDarken alpha:1]; [imageView.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width,self.view.frame.size.height)];
CGContextSetBlendMode(ctx, kCGBlendModeDarken);
imageView.image = UIGraphicsGetImageFromCurrentImageContext();
No need to keep imageview do it like this..
Since you are drawing on two different context you wont be able to use blend modes across them. For that you need to draw other stuff on your drawing view and then draw your image..
- (void)drawRect:(CGRect)rect {
// do ur drawing stuff first
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, 0, self.bounds.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
CGContextDrawImage(context, self.bounds, self.image.CGImage);
CGContextSetBlendMode(context, kCGBlendModeSaturation);
CGContextSetRGBFillColor(context, 0.0, 0.0, 0.0, 1.0);
CGContextFillRect(context, rect);
}
I would like to rewrite the Apple source code, GLPaint application, but not using OpenGL like the example, I would like to use Core Graphics library. But I stuck in displaying the texture like GLPaint.
This is my code in Core Graphics:
- (void) drawLineFromPoint: (CGPoint) fromPoint toPoint: (CGPoint) toPoint {
UIGraphicsBeginImageContext(self.frame.size);
CGContextRef context = UIGraphicsGetCurrentContext();
[drawImage.image drawInRect:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height)];
UIImage * image = [UIImage imageNamed:#"Particle.png"];
UIColor * color = [UIColor colorWithPatternImage:image];
CGContextSetStrokeColorWithColor(context, color.CGColor);
CGContextSetLineCap(context, kCGLineCapRound);
CGContextSetLineWidth(context, 5.0);
CGContextBeginPath(context);
CGContextMoveToPoint(context, fromPoint.x, fromPoint.y);
CGContextAddLineToPoint(context, toPoint.x, toPoint.y);
CGContextStrokePath(context);
drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}
--- But I receive this result:
--- I would like to have this result:
Does my code wrong? Any one can help me on this? Thank you very much.
If you don't want the pattern, don't set a colour with a pattern image as your stroke colour.
Instead of
UIImage * image = [UIImage imageNamed:#"Particle.png"];
UIColor * color = [UIColor colorWithPatternImage:image];
Just do
UIColor *color = [UIColor blackColor];
Kindly make sure you have the Particle.png added to the project. Also check the constants kBrushScale and kPalette* in GLPaint code.
I'm currently drawing a line using Core Graphics. It's really bare bones and simple.
- (void)drawRect:(CGRect)rect {
CGContextRef c = UIGraphicsGetCurrentContext();
CGFloat red[4] = {1.0f, 0.0f, 0.0f, 1.0f};
CGContextSetStrokeColor(c, red);
CGContextBeginPath(c);
CGContextMoveToPoint(c, 5.0f, 5.0f);
CGContextAddLineToPoint(c, 300.0f, 600.0f);
CGContextSetLineWidth(c, 25);
CGContextSetLineCap(c, kCGLineCapRound);
CGContextStrokePath(c);
}
This works well. Let's say that we wanted to draw a custom style line. Say we wanted to imitate the style of a crayon for example. And that the designer handed your crayon style images: http://imgur.com/a/N40ig
To do accomplish this effect I think I need to do something like this:
Create a special colored versions of crayonImage1-crayonImage4
Every time you add a line to line you use one of the crayonImages
You alternate the crayonImages every time you draw a point.
Step 1 makes sense. I can use the following method:
- (UIImage *)image:(UIImage *)img withColor:(UIColor *)color {
// begin a new image context, to draw our colored image onto
UIGraphicsBeginImageContext(img.size);
// get a reference to that context we created
CGContextRef context = UIGraphicsGetCurrentContext();
// set the fill color
[color setFill];
// translate/flip the graphics context (for transforming from CG* coords to UI* coords
CGContextTranslateCTM(context, 0, img.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
// set the blend mode to color burn, and the original image
CGContextSetBlendMode(context, kCGBlendModeColorBurn);
CGRect rect = CGRectMake(0, 0, img.size.width, img.size.height);
CGContextDrawImage(context, rect, img.CGImage);
// set a mask that matches the shape of the image, then draw (color burn) a colored rectangle
CGContextClipToMask(context, rect, img.CGImage);
CGContextAddRect(context, rect);
CGContextDrawPath(context,kCGPathFill);
// generate a new UIImage from the graphics context we drew onto
UIImage *coloredImg = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
//return the color-burned image
return coloredImg;
}
I'm unsure how I can complete steps 2 and 3. Is there an API in CoreGraphics for setting an image as the point of line? If so what is it and how can I use it?
Thanks in advance,
-David
Start with the following example: http://www.ifans.com/forums/showthread.php?t=132024
But for brushes, don't draw a line. Simply draw the brush image using CGContextDrawImage.
Basically, you simply draw an image for every touch.