I am new to Objective-C and iOS development. I have a view with some figures drawn by core drawing. Now I want to fill those shapes with color and I don't know the path or context of shape. Does Objective-C have any function like flood-fill or put-pixel so that by having only the stroke color I can fill any shape inside my view.
-(void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 4.0);
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGFloat components[] = {1.0, 0.0, 0.0, 1.0};
CGColorRef color = CGColorCreate(colorspace, components);
CGContextSetStrokeColorWithColor(context, color);
CGContextMoveToPoint(context, 50, 0);
CGContextAddLineToPoint(context, 0,320);
CGContextStrokePath(context);
CGColorSpaceRelease(colorspace);
CGColorRelease(color);
CGContextSetLineWidth(context, 2.0);
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
CGContextSetRGBFillColor(context, 0, 255, 0, 1.0);
CGContextMoveToPoint(context, 100, 100);
CGContextAddLineToPoint(context, 150, 150);
CGContextAddLineToPoint(context, 100, 200);
CGContextAddLineToPoint(context, 50, 150);
CGContextAddLineToPoint(context, 100, 100);
CGContextStrokePath(context);
CGContextSetLineWidth(context, 2.0);
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
CGRect rectangle = CGRectMake(60,170,200,80);
CGContextAddEllipseInRect(context, rectangle);
CGContextStrokePath(context);
}
This will make a circle and a square with some common region. I want a particular region to fill with color when a user taps that region.
So you are looking for flood fill in Objective C.
This is my implementation of Scan Line Flood Fill Algorithm.
Github : UIImageScanlineFloodfill
If you want to learn basic of flood fill:
Lode's Computer Graphics Tutorial Flood Fill
I hope this will help you.
Put your drawing code in the question and I can give you a specific answer.
Normally you just need to set a fill color using
[[UIColor redColor] setFill];
And any shapes you draw your core graphics will be filled with that color automatically.
Try this command:-
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
Core Graphics is closely tied to UIView and its drawRect: method and has a C interface. As you point out, you always draw in the current graphics context. I can think of 2 approaches: (1) When the user taps myView, set a property like myView.pointTapped, and in drawRect: find the shape to fill, set a fill color, and fill the closed path using GGGeometry methods.
There is an objective-C alternative: (2) Take a look at UIBezierPath. It's not as comprehensive as drawing in Core Graphics but it can be used in your ViewController implementation.
Related
I am trying to make an iPhone application with erasing. I am running into 2 problems, if you have a solution for either one please answer this. I would like to erase part of an image.
1) I am currently just clearing the rect but it has a square edge. I would like it to be round, I have previously tried translating but this does not work. I also need it to translate/rotate as few times as possible to maintain the same performance.
2) In addition I wanted to know if there are any other ways of erasing. When erasing fast it is erasing ever 1/2 inch. Is there a way to stroke a path and clear the rect or something? Sorry if this is hard to understand.
CGRect circleRect = CGRectMake([touch CGPointValue].x, [touch CGPointValue].y, 25, 25);
CGContextClearRect(currentContext,circleRect);
This code should do what you're looking for:
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineCap(context, kCGLineCapRound);
CGContextSetLineWidth(context, self.strokeWidth);
CGContextSetBlendMode(context, kCGBlendModeClear);
CGContextSetStrokeColorWithColor(context, [[UIColor clearColor] CGColor]);
CGContextBeginPath(context);
CGContextMoveToPoint(context, lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(context, currentPoint.x, currentPoint.y);
CGContextStrokePath(context);
CGContextFlush(context);
The key points are
1) CGContextSetLineCap(context, kCGLineCapRound), which makes it round
2) CGContextSetBlendMode(context, kCGBlendModeClear) which clears the context.
I realize this is an older question but I thought I would expand on Eric Reids answer as I was trying to use his example outside of the drawRect method and had to modify it to get it to work with a context I created in a 'touchesMoved' method in a UIView subclass.
I call this method from 'touchesMoved' and pass it the CGPoint of the touch in the view I'm drawing in.
-(void) processEraseAtPoint:(CGPoint)point
{
// setup a context with the size of our canvas view (the canvas view is the UIView instance I'm drawing into)
UIGraphicsBeginImageContext(self.canvasView.bounds.size);
// get a reference to the context we just created
CGContextRef context = UIGraphicsGetCurrentContext();
// draw the image we want to edit into this context (this is the image containing the drawing I want to erase part of)
[self.canvasView.incrementalImage drawAtPoint:CGPointZero];
// set our context options
CGContextSetLineCap(context, kCGLineCapRound);
CGContextSetLineWidth(context, self.canvasView.settings.brushDiameter);
CGContextSetBlendMode(context, kCGBlendModeClear);
// make the color clear since we're erasing
CGContextSetStrokeColorWithColor(context, [[UIColor clearColor] CGColor]);
// start our path in this context
CGContextBeginPath(context);
// set our first point
CGContextMoveToPoint(context, lastTouch.x, lastTouch.y);
// draw from our last point to this point
CGContextAddLineToPoint(context, point.x, point.y);
// stroke this path (in this case it's clear so it will erase what's there)
CGContextStrokePath(context);
// set our incrementalImage in the canvasView with the updated image from this context
// Note that in the canvasView 'drawRect' method I am calling
// '[self.incrementalImage drawInRect:rect]', so this new image will get drawn
// in my canvasView when I call 'setNeedsDisplay'
self.canvasView.incrementalImage = UIGraphicsGetImageFromCurrentImageContext();
// cleanup our context
CGContextFlush(context);
UIGraphicsEndImageContext();
// set our last touch point for the next line segment
lastTouch = point;
// update our view
[self.canvasView setNeedsDisplay];
}
Very frustrating experience understanding UIGraphicsPushContext(context) and UIGraphicsPopContext()
My understanding is that I can set attributes of the context like the stroke color and then push the context on a stack so I can set a new color for the current context. When I'm done doing that I can return to the context by popping it.
Below is my code. When I run the code below two lines are drawn in blue. What I expect to happen is: that I first set the color green. Go to the blueLine function and push the green context. Draw in blue. Then pop the green context. Allowing the drawLine function to drawn in green.
Here is a screenshot of what is drawn (two blue lines): http://dl.dropbox.com/u/1207310/iOS%20Simulator%20Screen%20shot%20Feb%205%2C%202012%209.00.35%20PM.png
Any help is GREATLY appreciated! Thank you.
- (void)drawBlueLine:(CGContextRef)context
{
UIGraphicsPushContext(context);
[[UIColor blueColor] setStroke];
CGContextBeginPath(context);
CGContextMoveToPoint(context, self.bounds.origin.x, 100);
CGContextAddLineToPoint(context, self.bounds.origin.x+self.bounds.size.width, 200);
CGContextStrokePath(context);
UIGraphicsPopContext();
}
- (void)drawLine:(CGContextRef)context
{
UIGraphicsPushContext(context);
CGContextBeginPath(context);
CGContextMoveToPoint(context, self.bounds.origin.x, 200);
CGContextAddLineToPoint(context, self.bounds.origin.x+self.bounds.size.width, 300);
CGContextStrokePath(context);
UIGraphicsPopContext();
}
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
[[UIColor redColor] setStroke];
CGContextSetLineWidth(context, 5.0);
[self drawBlueLine:context];
[self drawLine:context];
}
Or shouldn't this work?
- (void)drawLine:(CGContextRef)oldContext
{
UIGraphicsPushContext(oldContext); //makes oldContext the current context but there is a copy on the stack
[[UIColor blueColor] setStroke];
CGContextBeginPath(oldContext);
CGContextMoveToPoint(oldContext, self.bounds.origin.x, 200);
CGContextAddLineToPoint(oldContext, self.bounds.origin.x+self.bounds.size.width, 300);
CGContextStrokePath(oldContext);
UIGraphicsPopContext(); //previous oldContext is moved back into place containing red?
}
- (void)drawRect:(CGRect)rect
{
CGContextRef oldContext = UIGraphicsGetCurrentContext();
[[UIColor redColor] setStroke];
[self drawLine:oldContext];
//anything I draw here should be red. Shouldn't it?`
What UIGraphicsPushContext and UIGraphicsPopContext does as change which context is being used for drawing, not necessarily save and restore any given context's state. What your code is doing is simply repetitively replacing the context that was current prior to the call to drawRect: with the context you grab with UIGraphicsGetCurrentContext (they are likely to be the same anyway).
If you want to save an restore a given context's state, use CGContextSaveGState and CGContextRestoreGState instead.
The problem is the way you are setting the color, you need to use
CGContextSetStrokeColorWithColor(context, color)
like this:
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor)
and
CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor)
so that the color is connected to the context.
[[UIColor redColor] setStroke];
is changing the color for all strokes...I'm curious if it would overide the above function if it was set for the context, I think it would not...
I wondered if anyone knows how to get a shadaow effect like the one in things as per the screenshot. To me it looks like the shadow effect is created by having a shadow at the bottom of the cell above and the top of the cell below.
I can create the one from the cell above using the code below but can't figure out how to do it on the cell underneath as it doesn't get shown it's as if the cells are rendered in reverse order in terms of the z-index.
self.layer.shadowOffset = CGSizeMake(0, 2);
self.layer.shadowColor = [[UIColor blackColor] CGColor];
self.layer.shadowRadius = 2;
self.layer.shadowOpacity = 0.5;
CGFloat top = self.layer.bounds.origin.y;
CGFloat left = self.layer.bounds.origin.x;
CGFloat width = self.layer.bounds.size.width;
CGRect shadowFrame = CGRectMake(left, top, width, 44);
CGPathRef shadowPath = [UIBezierPath bezierPathWithRect:shadowFrame].CGPath;
self.layer.shadowPath = shadowPath;
Any suggestions much appreciated.
Things http://www.purplesmash.com/images/Things.jpg
Just create hollow rectangle while drawing with CoreGraphics (align it exactly that hollow part cover your cell visible view) and set shadow for context - this will save performance for you.
UPDATE:
I've tried this inside my cell drawRect: method
// Creating path which will hold our hollow rectangle
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddRect(path, NULL, CGRectMake(-8.0f, -8.0f, 336.0f, 96.0f));
CGPathAddRect(path, NULL, CGRectMake(-5.0f, 0.0f, 330.0f, 80.0f));
// Saving current graphics context state
CGContextSaveGState(context);
// Configuring shadow
CGContextSetShadowWithColor(context, CGSizeMake(0.0f, 0.0f), 6.0f,
[[UIColor blackColor] CGColor]);
// Adding our path
CGContextAddPath(context, path);
// Configure hollow rectangle fill color
CGContextSetRGBFillColor(context, 1.0, 1.0, 1.0, 1.0);
// Fill rectangle and keep hollow part transparent
CGContextEOFillPath(context);
// Restore graphics context
CGContextRestoreGState(context);
Of course additional improvement will be pre-calculate CGMutablePathRef path somewhere in initialization or in this method by condition if(path == NULL). Colors can be retained too. If this should be last row of your cell update, than maybe you don't event need to save context state.
You probably need to do this by drawing the shadows as part of the checked cell instead of setting the shadow properties on the surrounding cells.
I'd do it by adding one or two CAGradientLayers as children of the checked cell's contentView.layer.
I have edited this in light of the suggestion from moonlight. I put that code into a method addInnerTopShadow when a cell needs that I call the method. I have added another method addInnerBottomShadow which puts in the shadow at the bottom.
I call these methods in the drawRect method and when I want to change between the states I call the method:
[cell setNeedsDisplay];
This allows me to toggle the state of the cell without doing things like
[self.tableView reloadData];
As the methods suggest I have outer shadow methods that put a shadow on the first and last cells but that's another issue and has been answered many times. I now have my app working exactly how I want. So thanks to Rob and Moonlight.
-(void)addInnerBottomShadow
{
CGContextRef context = UIGraphicsGetCurrentContext();
// Creating path which will hold our hollow rectangle
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddRect(path, NULL, CGRectMake(0, 44, 480, 80));
CGPathAddRect(path, NULL, CGRectMake(0, 54, 480, 96));
// Saving current graphics context state
CGContextSaveGState(context);
// Configuring shadow
CGContextSetShadowWithColor(context, CGSizeMake(0.0f, 0.0f), 6.0f, [[UIColor blackColor] CGColor]);
// Adding our path
CGContextAddPath(context, path);
// Configure hollow rectangle fill color
CGContextSetRGBFillColor(context, 1.0, 1.0, 1.0, 1.0);
// Fill rectangle and keep hollow part transparent
CGContextEOFillPath(context);
CGContextClipToRect(context, self.bounds);
// Restore graphics context
CGContextRestoreGState(context);
}
-(void)addInnerTopShadow
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddRect(path, NULL, CGRectMake(-8.0f, -8.0f, 336.0f, 96.0f));
CGPathAddRect(path, NULL, CGRectMake(-5.0f, 0.0f, 330.0f, 80.0f));
// Saving current graphics context state
CGContextSaveGState(context);
// Configuring shadow
CGContextSetShadowWithColor(context, CGSizeMake(0.0f, 0.0f), 7.0f, [[UIColor blackColor] CGColor]);
// Adding our path
CGContextAddPath(context, path);
// Configure hollow rectangle fill color
CGContextSetRGBFillColor(context, 1.0, 1.0, 1.0, 1.0);
// Fill rectangle and keep hollow part transparent
CGContextEOFillPath(context);
CGContextClipToRect(context, self.bounds);
// Restore graphics context
CGContextRestoreGState(context);
}
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.
trying to draw circle divided to dynamically provided number of sectors. In the end my circle should look like pie.
I've created class Circle which contains number of Pies inside. Circle has method - (void)draw which calles [pie draw]; in for (Pie *pie in self.pies) loop.
Implementation of pie looks like this:
- (void)draw {
CGContextRef context = UIGraphicsGetCurrentContext();
float startAngleRads = degreesToRadians(_startAngle);
float endAngleRads = degreesToRadians(_endAngle);
CGContextBeginPath(context);
CGContextSetLineWidth(context, 1.0f);
CGContextSetLineCap(context, kCGLineCapRound);
CGContextSetLineJoin(context, kCGLineJoinRound);
CGColorRef strokeColor = [_strokeColor CGColor];
CGContextSetStrokeColorWithColor(context, strokeColor);
CGColorRef fillColor = [_bgColor CGColor];
CGContextSetFillColorWithColor(context, fillColor);
CGContextMoveToPoint(context, _x, _y);
CGContextAddArc(context, _x, _y, _r, startAngleRads, endAngleRads, YES);
CGContextDrawPath(context, kCGPathStroke);
CGContextFlush(context);
}
This draws nice circle with sectors but without any filling of course. When I change last lines to CGContextDrawPath(context, kCGPathStrokeFill); my stroke lines disappears and only last line (last sector) stays at the screen, other parts of circle are filled with bgcolor and no stroke is visible anymore.
The question is: how can I draw completly separated "sectors" (every sector should look like triangle with Arc and Stroke and Fill). I need this because I want to toggle visibility of that sectors but at the moment I cant even figure out how to draw them correctly.
If this is important, all drawing happens on the layer with self.opaque = NO;.
Ok, found my error: had to set NO in CGContextAddArc call.