CT-DW: drawing with CoreText in bitmap context on background thread causes exception

[triplef]

Using the CT-DW branch (see #925), calling CTLineDraw() on a background thread to draw into a bitmap context causes the following exception:

E/WIL: E:\repo\WinObjC\WinObjC_Internal\Source\winmd2objc\ObjCUWP\ObjCUWP\projections\WindowsGraphicsDisplay.mm(46)\(null)!00C511D2: (caller: 0140B4AC) Objective-C Exception(1) tid(130) 80070490 Element not found.
    [+[WGDDisplayInformation getForCurrentView](_comInst->GetForCurrentView(unmarshalledReturn.GetAddressOf()))]

This can be reproduced by calling the following code on a background thread:

NSString *text = @"Test";

CGColorRef myCGColor = [UIColor blackColor].CGColor;
CTFontRef myCFFont = CTFontCreateWithName((__bridge CFStringRef)@"Helvetica", 20, NULL);
NSDictionary *attributesDict = @{(id)kCTFontAttributeName: (__bridge id)myCFFont,
                                 (id)kCTForegroundColorAttributeName: (__bridge id)myCGColor};

CGSize contextSize = CGSizeMake(1000, 1000);
CGColorSpaceRef colSpace = CGColorSpaceCreateDeviceRGB();
void*   bitmapData = malloc(contextSize.width*contextSize.height*4);
CGContextRef bitmapContext = CGBitmapContextCreate(bitmapData, contextSize.width, contextSize.height, 8, contextSize.width*4, colSpace, kCGImageAlphaPremultipliedFirst|kCGBitmapByteOrder32Host);
CGColorSpaceRelease(colSpace);

CGContextSetRGBFillColor(bitmapContext, 0, 0.0, 0.0, 1);
CGContextFillRect(bitmapContext, CGRectMake(0.0, 0.0, contextSize.width, contextSize.height));
CGContextSetRGBFillColor(bitmapContext, 1,1,1,1);
CGContextSetTextMatrix(bitmapContext, CGAffineTransformIdentity);

CFAttributedStringRef attrString = CFAttributedStringCreate(kCFAllocatorDefault, (__bridge CFStringRef)text, (__bridge CFDictionaryRef)attributesDict);
CTLineRef line = CTLineCreateWithAttributedString(attrString);
CGContextSetTextPosition(bitmapContext, 1, floorf(contextSize.height/5)+1);

CTLineDraw(line, bitmapContext);

[rajsesh]

@triplef thanks for trying this out early and providing feedback.