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Re: Bug: ImageBuffer::alpha not initialised on X11 [message #15589 is a reply to message #15575]

Tue, 29 April 2008 19:33

mirek
Messages: 14267
Registered: November 2005

Ultimate Member

mrjt wrote on Tue, 29 April 2008 08:34

The alpha channel is not correctly initialised on X11. This causes corruption (second image is what it should look like):
index.php?t=getfile&id=1177&private=0

Everything works correctly for Win32. The code below exibits the problem:

class ImageDrawTest : public TopWindow {
public:
	typedef ImageDrawTest CLASSNAME;
	Image img;
	
	ImageDrawTest() {
		Sizeable();
		GenerateImage();
	}
	
	void GenerateImage() {
		Size sz(100, 100);
		ImageDraw w(sz);
//		w.Alpha().DrawRect(sz, Black());
		w.Alpha().DrawRect(30, 30, 40, 40, White());
		w.DrawRect(sz, Red);
		img = w;
	}
	
	virtual void Paint(Draw &w) {
		w.DrawRect(GetSize(), SColorFace());
		w.DrawImage(0, 0, img);	
	}
	
	virtual void LeftUp(Point p, dword keyflags) {
		GenerateImage();	
		Refresh();
	}
};

If you uncomment the line above, the channel is initialised and everything works correctly.

Edit: Looking at the manual for XCreatePixmap, it says the pixmap contents are undefined, which I guess is fair enough. My main issue here is the inconsistency between Win32/Linux, both should be either defined or undefined.

Well, this is rather missing docs... It was intended to have both "body" and "alpha" uninitialized, the same situation as with e.g. Paint. After all, you never know whether for specific use it is better to have alpha =0 or 255 (or even something else).

OTOH, if you believe it should be initialized, we can do that too.

Mirek

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