[Qt-interest] Painting on QImage vs. QPixmap

[Jesús Fernández]

Because QPixmap is designed to use it as a QPaintDevice.

2009/3/24 Brad Howes <howes at ll.mit.edu>

>
> On Mar 24, 2009, at 1:04 PM, Jesús Fernández wrote:
>
> From http://doc.trolltech.com/4.5/qpixmap.html:
>
>
>> Qt provides four classes for handling image data: QImage<http://doc.trolltech.com/4.5/qimage.html>,
>> QPixmap, QBitmap <http://doc.trolltech.com/4.5/qbitmap.html> and QPicture<http://doc.trolltech.com/4.5/qpicture.html>.
>> *QImage <http://doc.trolltech.com/4.5/qimage.html> is designed and
>> optimized for I/O, and for direct pixel access and manipulation, while
>> QPixmap is designed and optimized for showing images on screen.* QBitmap<http://doc.trolltech.com/4.5/qbitmap.html>is only a convenience class that inherits QPixmap, ensuring a depth of 1.
>> The isQBitmap <http://doc.trolltech.com/4.5/qpixmap.html#isQBitmap>()
>> function returns true if a QPixmap object is really a bitmap, otherwise
>> returns false. Finally, the QPicture<http://doc.trolltech.com/4.5/qpicture.html>class is a paint device that records and replays
>> QPainter <http://doc.trolltech.com/4.5/qpainter.html> commands.
>>
> Thanks anyway ;)
>
>
> For what? I knew that blurb but was curious as to the actual circumstances
> when one would be faster than the other. The blurb does not indicate that
> drawing into a QPixmap would be faster than QImage, and yet that can be
> true.
>
> Brad
>
>  --
> Brad Howes
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