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Native Development

New Contributor
Posts: 2
Registered: ‎11-27-2012
My Device: 9000
My Carrier: XL Axiata

Crop image into certain shape

hi there is there any way to crop image into certain image such as ellipse or triangle ? or can image.copy() handle copying image pixel by pixel. 

if anyone has already made a method to crop a circular shape on an image please let me know 


best regards



Posts: 18
Registered: ‎03-30-2012
My Device: Playbook
My Carrier: Ropdgers

Re: Crop image into certain shape

Posts: 508
Registered: ‎01-19-2011
My Device: My Trusty Red Plane
My Carrier: Outer Space

Re: Crop image into certain shape

yes there is, and it's pretty straightforward.


take a look at this


bb::cascades::Image Triangle::fromQImage(const QImage &origQImage, Color color)
	bb::ImageData imageData(bb::PixelFormat::RGBA_Premultiplied, origQImage.width(), origQImage.height());
	int y = 0;

	unsigned char *dstLine = imageData.pixels();

	float red = color.red();
	float green = color.green();
	float blue = color.blue();

	for (y = 0; y < origQImage.height(); y++)
		unsigned char * dst = dstLine;
		for (int x = 0; x < imageData.width(); x++)
			QRgb srcPixel = origQImage.pixel(x, y);

//			*dst++ = qRed(srcPixel) * qAlpha(srcPixel) / 255;
//			*dst++ = qGreen(srcPixel) * qAlpha(srcPixel) / 255;
//			*dst++ = qBlue(srcPixel) * qAlpha(srcPixel) / 255;
//			*dst++ = qAlpha(srcPixel);

			*dst++ = red * qAlpha(srcPixel);
			*dst++ = green * qAlpha(srcPixel);
			*dst++ = blue * qAlpha(srcPixel);
			*dst++ = qAlpha(srcPixel);

		dstLine += imageData.bytesPerLine();

	return Image(imageData);


This is my code to create a one-colored Image which keeps the alpha values of my mask image. the inner loop is the key. What I am doing is using the mask image pixel by pixel, reading it's alpha value and multiply it with my color. That way I can use any image with alpha values between 0.0 and 1.0 (so, my 'Shape') to create e.g. a red version WITHOUT any structures


Since you want to create an image with a specific shape, just apply my function, but instead of multiplying it with a certain color, just give the function a second image, and put something like


*dst++ = qRed(imagePixel) * qAlpha(shapePixel) / 255;


in the inner loop. That should give you a bb::cascades::Image with your shape


Keep in mind that the function requires a QImage, not a bb::cascades::Image, but returns a bb::cascades::Image


If you aren't afraid of a bit of source code, take a look at the Carousel-example, which creates a mirrorred image by merging two images together (one of them flipped)



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