Core Graphics drawing only black - iphone

Question

I'm trying to develop a chess game on the iPhone, and have become stuck on an otherwise insignificant detail but can not seem to get past it. Can anybody see the piece that's missing?
Here's the problem. When a user clicks on a square, it should highlight in some faded color. What actually is happening though, is it just draws black, totally regardless of what color I set it to.
Here's an image of what I get. The black circle should be red, or any color.
Here, notice the UIView I'm drawing to is behind the pieces view. Doubt it matters, but I want to be complete.
Finally, the code for the layer:
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
// Initialization code
self.backgroundColor = [UIColor clearColor];
rowSelected = 0;
colSelected = 0;
}
return self;
}
-(void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextClearRect(context, rect);
CGContextSetRGBStrokeColor(context, 255.0, 0.0, 0.0, 1.0);
if (rowSelected && colSelected)
{
int gridsize = (self.frame.size.width / 8);
int sx = (colSelected-1) * gridsize;
int sy = (rowSelected-1) * gridsize;
int ex = gridsize;
int ey = gridsize;
CGContextFillEllipseInRect(context, CGRectMake(sx,sy,ex,ey));
}
}
// Handles the start of a touch
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
int gridsize = (self.frame.size.width / 8);
// Position of touch in view
UITouch *touch = [[event allTouches] anyObject];
CGPoint loc = [touch locationInView:self.superview];
int x = loc.x / gridsize;
int y = loc.y / gridsize;
rowSelected = y + 1;
colSelected = x + 1;
[self setNeedsDisplay];
}
I have tried a number of things, using a value of 1 rather than 255, playing with the alpha, etc, but I can't get anything other than a solid black.
EDIT:
Also, here's the code of this view's superview:
#implementation ChessBoard
-(id)initWithFrame:(CGRect)frame
{
if (self != [super initWithFrame:frame])
return self;
int SQUARE_SIZE = frame.size.width / 8;
currentSet = BW;
UIImage *img = [UIImage imageNamed:#"board.png"];
background = [[UIImageView alloc] initWithImage:img];
[background setFrame:frame];
[self addSubview:background];
overlay = [[ChessBoardOverlay alloc] initWithFrame:frame];
[self addSubview:overlay];

Answer 1

In the function CGContextSetRGBStrokeColor color compontent values (red, green,blue, alpha) need to be between 0 and 1. Since you are assuming that 255 is the maximum for a color you need to divide all of your color component values by 255.0f.
CGContextSetRGBStrokeColor(context, 255.0f/255.0f, 0.0/255.0f, 0.0/255.0f, 1.0);

Answer 2

You say you're drawing to a layer... but a CALayer doesn't have a drawRect: method, it has drawInContext:
I would guess by trying to call drawRect: in your instance of a CALayer that the true context hasn't been built correctly, or it has but you're not tying in to it.

Answer 3

Maybe you should state your color this way:
CGContextSetRGBStrokeColor(context, 255.0/255.0f, 0.0/255.0f, 0.0/255.0f, 1.0f);
This happened to me once using:
[UIColor colorWithRed:12.0/255.0f green:78.0/255.0f blue:149.0/255.0f alpha:1.0f];
until I added the /255.0f so that may work.