How to render (bitmap) only part of a Visual?

Question

I must print a displayed TreeView.

Rendering the root TreeViewItem to bitmap, gives me an image of the whole (even non visible nodes) tree. Then I split the bitmap in "pages" to be printed. The rendering code:

m_Bitmap = new RenderTargetBitmap((int)l_RootTreeViewItem.ActualHeightDesiredSize.Width,
                                  (int)l_RootTreeViewItem.ActualHeight, 96, 96,
                                  PixelFormats.Pbgra32);

m_Bitmap.Render(l_RootTreeViewItem);

Works well for small size trees. If the tree is large, RenderTargetBitmap results in "Out Of Memory" Exception.

So, the idea is to render only parts of the visual to avoid memory problems. A Render method where I can choose which part of visual to render will be perfect...

m_Bitmap.Render(l_RootTreeViewItem, xOffset, yOffset, width, height);

... but doesn't exist. Is there some way to do that ?

Nicolas Repiquet Nicolas Repiquet · Accepted Answer · 2012-04-25T07:45:44

What I'll do :

Create a VisualBrush of your l_RootTreeViewItem
Create a Rectangle and assign the visual brush to the Fill property
Play with VisualBrush.Viewbox and VisualBrush.Viewport to render the part of the tree view I'm interested in
Use RenderTargetBitmap.Render on my rectangle when needed

EDIT

Solution 2

Put l_RootTreeViewItem in a canvas
Set the ClipToBounds property of the canvas to true
Play with Canvas.Width, Canvas.Height properties and Canvas.Left, Canvas.Top attached properties to display only a part of the TreeViewItem

Use PrintDialog.PrintVisual on the canvas as needed.

<Canvas Width="300" Height="300" ClipToBounds="True">
    <TreeViewItem Canvas.Left="-200" Canvas.Top="-100">
        ...
    </TreeViewItem>
</Canvas>

How to render (bitmap) only part of a Visual?

1 Answers