QImageIOPlugin, support for new image format.

[suneel1310]

Hi,

We have created a plugin to support a new imageformat.
When i load the new image, it talks to the corresponding imagerenderer through plugin. and returns a qimage.
But I am not able to pass the size for this qimage to the plugin.
How to do it ?

or atleast, how to specify the new imageformat in the constructor with the size.
I did not find any QImage constructor for the same .

If I do,

QImage image(200, 200, QImage::Format_Invalid);
image.load("c:\\data\\sample.abc","abc")

it is not taking size (200, 200).
also, how in the constructor above how I can specify the new image format ??

Please help me in solving this problem.

[spud]

QImage::load() doesn't scale the image. It is supposed to return an image the size that is presumably specified in the file.
Also, Qt will know to use your plugin when encountering a ".abc" file if your plugin class reimplements QImageIOPlugin::keys() to return "abc".

[suneel1310]

QImage image(200, 200, QImage::Format_Invalid);
image.load("c:\\data\\sample.abc","abc")

ok,

In the plugin I have a QSize abcSize, and the image created from sample.abc is of size abcSize. So, how to pass the size (to the plugin) ?
In the aboe code, image size is abcSize, not (200,200). I want a QImage to be created of size (200,200) or any other size that we pass.

[spud]

Well you could always use
image.scale();

If you want more control, you should use QImageReader.

[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();
...
}
};



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

[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.