CODEWITHSUNDEEP
iosopengl-esuiimagegrand-central-dispatchquartz-2d
jfisk
jfisk

Reputation: 6205

How to generate a UIImage programmatically with Quartz 2D and Grand CEntral Dispatch

Right now i haven an image being generated on a tap programmatically with Quartz 2D. I wanted to use it in combination with grand central dispatch so it can be created on another cpu and trigger the usual fade in animation when its completed. Right now I use the follow code at the bottom of this post but im getting these invalid context errors. Is there a way to do this or am i out of luck?

CGContextTranslateCTM: invalid context 0x0 CGContextScaleCTM: invalid context 0x0 CGContextSaveGState: invalid context 0x0 CGContextSetCompositeOperation: invalid context 0x0 CGContextFillRects: invalid context 0x0 CGContextRestoreGState: invalid context 0x0 CGContextDrawImage: invalid context 0x0

my code:

    dispatch_group_t group = dispatch_group_create();
    dispatch_group_async(group, dispatch_get_global_queue(0, 0), ^{
        self.view.contentScaleFactor=[[UIScreen mainScreen] scale];
        CGSize sizeofText=[stopName sizeWithFont:[UIFont fontWithName:@"Helvetica-Bold" size:17.5*[self.view contentScaleFactor]]];
        CGSize size;
        size.width=1024;
        size.height=1024;

        UIImage *leftCap = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"leftcap@2x" ofType:@"png"]];
        UIImage *center = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"center@2x" ofType:@"png"]];
        UIImage *rightCap = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"rightcap@2x" ofType:@"png"]];
        UIImage *spike = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"spike@2x" ofType:@"png"]];
        UIGraphicsBeginImageContextWithOptions(size,false,0);

        CGContextRef context = UIGraphicsGetCurrentContext(); //get the context we just made above
        CGContextTranslateCTM(context, 0,size.height);
        CGContextScaleCTM(context, 1, -1);

        width=(19*[self.view contentScaleFactor])+(sizeofText.width)+(43*[self.view contentScaleFactor]);

        height=60*[self.view contentScaleFactor];

        //draw calls
        [leftCap drawInRect:CGRectMake(0,1024- 54.0f*[self.view contentScaleFactor], 19.0f*[self.view contentScaleFactor], 54.0f*[self.view contentScaleFactor])];    
        [center drawInRect:CGRectMake(19.0f*[self.view contentScaleFactor],1024- 54.0f*[self.view contentScaleFactor],(sizeofText.width), 54.0f*[self.view contentScaleFactor])];
        [rightCap drawInRect:CGRectMake((sizeofText.width)+19*[self.view contentScaleFactor],1024- 54.0f*[self.view contentScaleFactor], 43.0f*[self.view contentScaleFactor], 54.0f*[self.view contentScaleFactor])];
        [spike drawInRect:CGRectMake((width/2)-((32.0f*[self.view contentScaleFactor])/2.0f),1024-(43.5*[self.view contentScaleFactor])- 27.0f*[self.view contentScaleFactor], 32.0f*[self.view contentScaleFactor], 27.0f*[self.view contentScaleFactor])];

        CGContextSelectFont(context, "Helvetica-Bold", 17.5*[self.view contentScaleFactor], kCGEncodingMacRoman);
        CGContextSetTextDrawingMode(context, kCGTextFill);
        CGContextSetTextPosition(context,19.f*[self.view contentScaleFactor],1024- (7.5*[self.view contentScaleFactor])-(sizeofText.height));
        CGContextShowText(context, [stopName UTF8String], strlen([stopName UTF8String]));

        image=UIGraphicsGetImageFromCurrentImageContext();



        UIGraphicsEndImageContext();

    });



    dispatch_group_notify(group, dispatch_get_global_queue(0, 0), ^{
        NSLog(@"done. I would trigger the fade in animation ehre"); 
    });

Upvotes: 2

Views: 3682

Answers (1)

Tony Million
Tony Million

Reputation: 4296

I do something similar except I am using CGBitmapContextCreate in place of UIGraphicsBeginImageContextWithOptions. Looks like your context isn't being created - probably because you are calling a UI* function on a background thread.

CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();

CGContextRef _composedImageContext = CGBitmapContextCreate(NULL, 
                                              width, 
                                              height, 
                                              8, 
                                              width*4, 
                                              rgbColorSpace, 
                                              kCGImageAlphaPremultipliedFirst);

CGColorSpaceRelease( rgbColorSpace );


// draw your things into _composedImageContext

//finally turn the context into a CGImage
CGImageRef cgImage = CGBitmapContextCreateImage(_composedImageContext);

Upvotes: 4

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