QImageIOPlugin, support for new image format.

[suneel1310]

Thank you,
QImageReader worked for me.

But, if I use image.scale() ,, then it'll scale the original image to the vale passed in scale().

So, is there anything similar; to create a QIcon of specific size from a file?

[spud]

Have a look at QImageIOHandler::ImageOption, in specific QImageIOHandler::ScaledSize and QImageIOHandler::supportsOption().

class MyImageHandler : public QImageIOHandler
{
    ...
    bool supportsOption ( ImageOption option )
    {
        if(option==ScaledSize)
            return true;
        ...
    }
    bool read ( QImage * image ) 
    {
        QSize scaledSize = option(ScaledSize).toSize();
        ...
    }
};

class MyImageHandler : public QImageIOHandler
{
    ...
    bool supportsOption ( ImageOption option )
    {
        if(option==ScaledSize)
            return true;
        ...
    }
    bool read ( QImage * image ) 
    {
        QSize scaledSize = option(ScaledSize).toSize();
        ...
    }
};

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QImage icon(64, 64, QImage::Format_RGB32);
QImageReader reader("XXX.abc");
reader.setScaledSize(QSize(64,64);
if (reader.read(&icon)) {
     // Display icon
 }

QImage icon(64, 64, QImage::Format_RGB32);
QImageReader reader("XXX.abc");
reader.setScaledSize(QSize(64,64);
if (reader.read(&icon)) {
     // Display icon
 }

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[suneel1310]

Thank you.
QImage Reader solved my problem

Now, Is there anything similar in QPixmap?? like QImageReader for QImage.
Or, we should create QImage first and then converting it to QPixmap?

[spud]

Create a QImage and then convert it.

[suneel1310]

But, converting from QImage to Qpixmap is expensive, interms of performance.
So, isn't there any other approach? which is good in performance.

[spud]

It might be expensive, but not necessarily. On windows each QPixmap internally holds a QImage, so it is virtually for free. Anyway it is unavoidable. You first need to load the image from the hard drive into RAM buffer. You do this by loading a Qimage. You then want to transfer the image to your screen buffer(be it an X-Server, or an OpenGL texture). You do this by converting the QImage to a QPixmap.

It is only expensive in the sense that it is wasteful to convert back and forth within a paintEvent(). You still have to do the conversion once, so that subsequent manipulations of the QPixmap(rotations, scaling etc) make best use of the underlying rendering system.

I hope that the answer makes sense to you.

[suneel1310]

Yes,
Thanks a lot for that info.
It really helped me.

[talk2amulya]

spud: that was really helpful info. just one question. is it QImage that contains a QPixmap or a QPixmap that contains a QImage...in windows..

[spud]

QPixmap contains a QImage.