How to print a part of an Item?

cq_qt

An Item has a huge size. Let's say 500000X500000. And the Item has thousands of childItems.
Then I want to print a part of this Item(including its children), the letftop is a point in this Item,the width and height are 3000 pixels.
I found the method of QQuickItem::grabToImage that can grab the whole Item.But I don‘t find a method can grab a part of an Item.
Is there a method that can grab a part of Item into Image?

fcarney

You realize that without compression that would be a 1 Terabyte image?
What can possibly take 500K x 500K pixels to produce?

cq_qt

you are right. I changed my question.

fcarney

I would look into using a shader effect from qml to render a portion of the larger item to a smaller item. Then use grabToImage on that smaller item. I know there are ways to cut pieces using the shader effects. I just cannot remember which one to use.

sierdzio

You can specify the target size in functions parameter: https://doc.qt.io/qt-5/qquickitem.html#grabToImage-1. The QML version also has target size https://doc.qt.io/qt-6/qml-qtquick-item.html#grabToImage-method

GrecKo

That's the target size, not the source rect which OP seems to want. As mentionned by fcarney you could get a part of the item by calling grabToImage on a ShaderEffectSource with sourceItem and sourceRect set accordingly.

sierdzio

You can also call grabToImage on an Item that you manually set to correct size.