Does anyone know how to animate a radar animation like the image below?
alt text http://img197.imageshack.us/img197/7124/circle0.png
With it growing outwards? I have to draw the circle using Quartz or some other way?
To draw a static circle in a UIView subclass:
- (void)drawRect:(CGRect)rect
{
CGRect rect = { 0.0f, 0.0f, 100.0f, 100.0f };
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetRGBStrokeColor(context, 1.0, 0.0, 0.0, 1.0);
CGContextSetLineWidth(context, 2.0f);
CGContextAddEllipseInRect(context, rect);
CGContextStrokePath(context);
}
From there you just need to animate it with a timer, vary the size of the rect, and add more circles.
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
I have a CGContextRef and can draw on it and specify the alpha, and if I try and use it it works perfectly. However, I am trying to colourise it (currently either red or green), but whatever blend mode I choose, the alpha is set to 1 (because I am drawing with alpha as 1). Drawing it the correct colour is not really a viable option, as I would like to be able to colour UIImages loaded from the filesystem as well, so how should I achieve this?
Edit: Example code (width and height are predefined floats, points is an array of CGPoints all of which lie inside the context and color is a UIColor with an opacity of 100%) -
UIGraphicsBeginImageContext(CGSizeMake(width,height));
CGContextRef contextRef = UIGraphicsGetCurrentContext();
CGContextClearRect(contextRef, CGRectMake(0.0f, 0.0f, width, height));
CGContextSetRGBStrokeColor(contextRef, 0.0f, 0.0f, 0.0f, 1.0f);
CGContextSetRGBFillColor(contextRef, 1.0f, 1.0f, 1.0f, 1.0f);
CGContextSetLineWidth(contextRef, lineWidth);
CGContextBeginPath(contextRef);
CGContextMoveToPoint(contextRef, points[0].x, points[0].y);
for (int i = 1; i < 4; i++) {
CGContextAddLineToPoint(contextRef, points[i].x, points[i].y);
}
CGContextAddLineToPoint(contextRef, points[0].x, points[0].y); // Encloses shape
CGContextDrawPath(contextRef, kCGPathFillStroke);
[color setFill];
CGContextBeginPath(contextRef);
CGContextSetBlendMode(contextRef, kCGBlendModeMultiply);
CGContextAddRect(contextRef, CGRectMake(0.0f, 0.0f, width, height));
CGContextDrawPath(contextRef, kCGPathFill);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
Thank you in advance for your help,
jrtc27
The problem was I needed a CGContextClipToMask. This meant my code required the following:
CGContextTranslateCTM(contextRef, 0, height);
CGContextScaleCTM(contextRef, 1.0, -1.0);
to convert the coordinates and then
CGRect rect = CGRectMake(0.0f, 0.0f, width, height);
CGContextClipToMask(contextRef, rect, UIGraphicsGetImageFromCurrentImageContext().CGImage);
to fix it.
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);
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.
Newbie Q.
I wish to subclass a UIView so that it renders a circle.
How is that done in an iPhone?
In the drawRect: method do:
- (void)drawRect:(CGRect)rect
{
CGContextRef ctx = UIGraphicsGetCurrentContext();
UIGraphicsPushContext(ctx);
CGContextSetRGBFillColor(ctx, 1.0f, 1.0f, 1.0f, 1.0f); // white color
CGContextFillEllipseInRect(ctx, CGRectMake(10.0f, 10.0f, 100.0f, 100.0f)); // a white filled circle with a diameter of 100 pixels, centered in (60, 60)
UIGraphicsPopContext();
}