I create a circle with a nice shadow with this code (I use MonoTouch.net for iPhone, Objective-C answers are fine of course)
UIGraphics.PushContext (ctx);
SizeF shadowSize = new SizeF (0f, -3f);
ctx.SetRGBFillColor (194f / 255f, 212f / 255f, 238f / 255f, 1f);
ctx.SetAllowsAntialiasing (true);
ctx.SetShadowWithColor (shadowSize, 20, new CGColor (0.9f, 0.7f));
RectangleF area = new RectangleF (35f, 15f, 210f, 210f);
ctx.FillEllipseInRect (area);
UIGraphics.PopContext ();
Then I want to add to it an arc and lines. When I do, the colors and shadow etc seem to stick around? How do I 'start fresh' while drawing my UIView ? (It's all in the same UIView; I am building up the image)
If you mean to clear everything that's drawn so you have a blank canvas, try CGContextClearRect before drawing anything.
But I think you mean that you want the shadow, fill color, etc. to only apply to that ellipse and not to the things that you draw afterward. To do that, you want to call the same state-setting methods again, but with different arguments. For instance, CGContextSetShadowWithColor expects a shadow color. But if you pass NULL for that argument, it will disable shadowing.
See also the CGContextSetShadow documentation, which has a note about all the ways you can disable shadowing. Pick the best one for you.
I think your main problem is that you're not taking advantage of Apple's excellent documentation. I gather that MonoTouch.net essentially maps Objective-C APIs to .NET modules with similar or identical symbol names. So with a quick Google search, you should be able to find the corresponding documentation in the iPhone OS Reference Library.
Before we begin drawing, save the state:
CGContextSaveGState(ctx);
Then after we are finished, return the state to what it was at the beginning:
CGContextRestoreGState(ctx);
Related
My current project contains a gravity simulator where sprites move in accordance with the forces they experience in the game scene.
One of my features involve allowing moving sprites to draw a line behind them so you can see what paths they take.
Shown here:
However, as the Sprite continues it's movements around the screen, the FPS begins to dive. This can be seen in this second image where some time has passed since the sprite first started its movement.
When researching, I found other people had posted with similar problems:
Multiple skshapenode in one draw?
However, in the question above, the answer's poster detailed that it (The answer) was meant for a static image, which isn't something I want, because this line will change in real time depending on what influences the sprites path, this was reflected when I tried implementing a function to add a new Line to the old one which didn't work. That Code here
I'm asking if anyone can assist me in finding a way to properly stop this constant FPS drop that comes from all the draw operations. My current draw code consists of two Functions.
-(void)updateDrawPath:(CGPoint)a B:(CGPoint)b
{
CGPathAddLineToPoint(_lineToDraw, NULL, b.x, b.y);
_lineNode.path = _lineToDraw;
}
-(void)traceObject:(SKPlanetNode *)p
{
_lineToDraw = CGPathCreateMutable();
CGPathMoveToPoint((_lineToDraw), NULL, p.position.x, p.position.y);
_lineNode = [SKShapeNode node];
_lineNode.path = _lineToDraw;
_lineNode.strokeColor = [SKColor whiteColor];
_lineNode.antialiased = YES;
_lineNode.lineWidth = 3;
[self addChild:_lineNode];
}
updateDrawPath: Draws line to latest position of Sprite.
traceObject: Takes SKPlanetNode (Subclass of SKSpriteNode), and sets it up to have a line drawn after it.
If anyone can suggest a way to do this and also reduce the terrible overhead I keep accumulating, it would be fantastic!
A couple suggestions:
Consider that SKShapeNode is more or less just a tool for debug drawing mostly, due to the fact that it doesn't draw in batches it's really not suitable to make a game around that or to use it extensively (both many shapes as well as few but complex shapes).
You could draw lines using a custom shader which will likely be faster and more elegant solution, though of course you may have to learn how to write shader programs first.
Be sure to measure performance only on a device, never the simulator.
I have read what I believe to be the relevant parts of the Quartz 2D Programming Guide, but cannot find an answer to the following (they don't seem to talk a lot about iOS in the document):
My application displays a drawing in a UIView. Every now and then I have to update the drawing in some way, e.g. change the fill colour of one of the shapes (I keep CGPathRefs to the important shapes to be able to redraw them with a different fill colour later). As described in the Section "Drawing With a CGLayer" on page 169 of the aforementioned document, I was thinking of drawing the entire drawing into a CGContext that I would obtain from a CGLayer, like so:
CGContextRef offscreenContext = CGLayerGetContext(offscreenLayer);
Then I could do my updating off-screen into the CGContext and draw the CGLayer into my UIView in the UIView's drawRect: method, like so:
CGContextDrawLayerAtPoint(viewContext, CGPointZero, offscreenLayer);
The problem I am having is, where do I get my CGLayer from? My understanding is I have to make it using CGLayerCreateWithContext and supply a CGContext as a parameter from which it inherits most of it's properties. Obviously, the right context would be the context of the UIView, that I am getting with
CGContextRef viewContext = UIGraphicsGetCurrentContext();
but if I am not mistaken, I can only get that within the drawRect: method and it is not valid to assume that the context I am given there will be the same one next time the method is called, i.e. I can only use that CGContext locally within the method.
So, how can I get a CGContext that I can use to initialise my CGLayer to create an offscreen CGContext to draw into and then draw the entire layer back into my UIView's CGContext?
PS: While you're at it; if anything above does not make sense or is not sane, please let me know. I am just starting to get my head around Quartz 2D.
First of all, if you are doing it from in an iOS environment, I think you are right. The documentation clearly said that the only way to obtain a CGContextRef is by
CGContextRef ctx = UIGraphicGetCurrentContext();
Then you use that context for creating the CGLayer with
CGLayerRef layer = CGLayerCreateWithContext(ctx, (CGSize){0,0}, NULL);
And if you want to draw on that layer, you have to draw it with the context you get from the layer. (It is somewhat different from the context you passed in earlier to create the CGLayer). Im guessing the CGLayerCreateWithContext saves the information it can get from the context passed in, but not everything. (One of the example is the ColorSpace information, you have to re-specify when you fill something with the context from CGLayer).
You can get the CGLayer context reference from the CGLayerGetContext() function and use that to draw.
CGContextRef layerCtx = CGLayerGetContext(layer);
CGContextBeginPath(layerCtx);
CGContextMoveToPoint(layerCtx, -10, 10);
CGContextAddLineToPoint(layerCtx, 100, 10);
CGContextAddLineToPoint(layerCtx, 100, 100);
CGContextClosePath(layerCtx);
One point that I found out is when you draw something offscreen, it automatically clips the thing offscreen. (make sense, so it doesnt draw things that is not seen) but when you move the layer (using the matrix transformation). The clipped path is not showing (missing).
One last thing, if you save the reference to a layer into a variable and later on you want to draw it, you can use CGContextDrawLayerAtPoint() method like
CGContextDrawLayerAtPoint(ctx, (CGPoint) {newPointX, newPointY}, layer);
It will sort of "stampt" or "draw" the layer at that newPointX and new PointY coordinate.
I hope that answer your question, if its not please let me know.
I'm drawing an oblong 'egg' shape (on iOS), and want to use it as a boundary for particles. My thought is to use the curve paths to make a UIView and then use hitTest:withEvent: or pointInside:withEvent: to enforce boundary collision.
The problem is, of course, that UIView is always rectangular. How would you go about checking to see if a point is inside an irregular shape like this?
- (void)drawRect:(CGRect)rect {
int w = rect.size.width;
int h = rect.size.height;
CGContextBeginPath(context);
CGContextMoveToPoint(context, w/2, h/5);
CGContextAddCurveToPoint(context, w*0.1, h/4.3, w*0.1, h*0.82, w/2, h*0.8);
CGContextAddCurveToPoint(context, w*0.9, h*0.82, w*0.9, h/4.3, w/2, h*0.2);
I'm using openFrameworks, for what that's worth. This code is just Obj-C but I'm open to any C++/obj-C++ solutions out there.
If you make a CGPathRef you can use CGPathContainsPoint. You can use that same CGPathRef to render into the context. You could also call CGContextPathContainsPoint on the context containing the path, but depending on when you need to test you might not have a context. And another alternative is the containsPoint selector on UIBezierPath.
If you want to code this from scratch, http://www.softsurfer.com/Archive/algorithm_0103/algorithm_0103.htm goes through a couple of different algorithms that will work for an arbitrary polygon.
I can combine rect1 with rect2 using CGRectUnion() and get a combined rect3 fine.
Is it possible to subtract a rect1 from a rect3 (which contains rect1) and get a remaining part of rect?
As Brad Larson said, you can't do this in Quartz, because the CGRect functions work with nothing but rects and their component parts (points, sizes, and single numbers).
If you were programming the Mac, I would suggest using another API named HIShape. It's the modern successor to QuickDraw Regions, and as such, it is capable of non-rectangular shapes. Unfortunately, though HIShape is still available on 64-bit Mac OS X, it is not available on iOS.
If you really need something like this, you will have to write it yourself, including your own HIShape-like not-necessarily-rectangular shape class.
Try CGRectIntersection if I could understand you correctly.
well, it depends... on how rect3 contains rect1...
i mean, it may happens that the resulting area is no more a rect...
for example, if rect1 is all inside rect3 the remaining area is not a rect, so you couldn't use the CGRect object.
You could obtain a rect just in case rect3 and rect1 share completely a side and have it (all of it) in common. So i need to know what kind of objet you wanna obtain by that subtraction...
may it be a new image with 2 different areas coloured? or slit the resuting area in more CGrect (upper rect, left, bitton, right...)
what are you going to do with the resulting "object"?
luca
Ultimately I'm working on a box blur function for use on iPhone.
That function would take a UIImage and draw transparent copies, first to the sides, then take that image and draw transparent copies above and below, returning a nicely blurred image.
Reading the Drawing with Quartz 2D Programming Guide, it recommends using CGLayers for this kind of operation.
The example code in the guide is a little dense for me to understand, so I would like someone to show me a very simple example of taking a UIImage and converting it to a CGLayer that I would then draw copies of and return as a UIImage.
It would be OK if values were hard-coded (for simplicity). This is just for me to wrap my head around, not for production code.
UIImage *myImage = …;
CGLayerRef layer = CGLayerCreateWithContext(destinationContext, myImage.size, /*auxiliaryInfo*/ NULL);
if (layer) {
CGContextRef layerContext = CGLayerGetContext(layer);
CGContextDrawImage(layerContext, (CGRect){ CGPointZero, myImage.size }, myImage.CGImage);
//Use CGContextDrawLayerAtPoint or CGContextDrawLayerInRect as many times as necessary. Whichever function you choose, be sure to pass destinationContext to it—you can't draw the layer into itself!
CFRelease(layer);
}
That is technically my first ever iPhone code (I only program on the Mac), so beware. I have used CGLayer before, though, and as far as I know, Quartz is no different on the iPhone.
… and return as a UIImage.
I'm not sure how to do this part, having never worked with UIKit.