Hi,
what is the best way to render a string and output it as an image in a
custom QC plugin?
I tried 2 approaches:
_1_ using NSAttributed string:
1. Create an NSAttributed String S
2. Convert S in a texture T with genTextureWithBounds
3. Create an outputImageProvider using T
..it works, but it is still a bit slow when I render houndreds of strings.
_2_ using Quartz2D primitives:
1. Create a bitmap context from QC context with CGBitmapContextCreate
2. Use Quartz2D functions to draw text on the context created
(CGContextSelectFont/CGContextShowTextAtPoint, etc)
3. Release the context created
4. Create an outputImageProvider
here is the code of the second approach:
////////////////////////////////////////////////////////////////
- (BOOL) execute:(id<QCPlugInContext>)context atTime:(NSTimeInterval)time
withArguments:(NSDictionary*)arguments
{
CGLContextObj cgl_ctx = [context CGLContextObj];
CGContextRef myContext;
/* Create CGContext and draw text into it */
myContext = CGBitmapContextCreate(baseAddress, w, h, 8, rowBytes,
[context colorSpace], kCGImageAlphaPremultipliedFirst |
kCGBitmapByteOrder32Host);
if(myContext == NULL) {
free(baseAddress);
return NO;
}
CGContextClearRect(myContext, CGRectMake(0,0,w, h));
CGContextSelectFont (myContext,
"Helvetica-Bold",
100,
kCGEncodingMacRoman);
CGContextSetCharacterSpacing (myContext, 10);
CGContextSetTextDrawingMode (myContext, kCGTextFill);
CGContextSetRGBFillColor (myContext, 1, 1, 1, 1);
CGContextShowTextAtPoint (myContext, 0, (h/2), "some text", 11);
/* We don't need context anymore */
CGContextRelease(myContext);
#if __BIG_ENDIAN__
_placeHolderProvider = [[context
outputImageProviderFromBufferWithPixelFormat:QCPlugInPixelFormatARGB8
pixelsWide:w pixelsHigh:h baseAddress:baseAddress bytesPerRow:rowBytes
releaseCallback:_BufferReleaseCallback releaseContext:NULL
colorSpace:[context colorSpace] shouldColorMatch:YES] retain];
#else
_placeHolderProvider = [[context
outputImageProviderFromBufferWithPixelFormat:QCPlugInPixelFormatBGRA8
pixelsWide:w pixelsHigh:h baseAddress:baseAddress bytesPerRow:rowBytes
releaseCallback:_BufferReleaseCallback releaseContext:NULL
colorSpace:[context colorSpace] shouldColorMatch:YES] retain];
#endif
self.outputImage = _placeHolderProvider;
return YES;
}
////////////////////////////////////////////////////////////////
..but this approach has got very low performance compared to the first one.
..are there other ways to output a string as an image? How can I improve
performance?
Thank you,
Luke
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