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POwpf apply transforms when drawing drag adorner
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  1. POwpf apply transforms when drawing drag adorner
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    copied!<p>In our drag and drop implementation, we like the adorner to apply the adorned element's transform value.</p> <p>The transform may apply to UIElements in Xaml like this:</p> <pre><code>&lt;DockPanel.LayoutTransform&gt; &lt;TransformGroup&gt; &lt;ScaleTransform ScaleX="0.75" ScaleY="0.75"/&gt; &lt;RotateTransform Angle="10" /&gt; &lt;/TransformGroup&gt; &lt;/DockPanel.LayoutTransform&gt; &lt;TextBlock&gt; &lt;TextBlock.LayoutTransform&gt; ... </code></pre> <p>This is how transforms are retrieved by summarizing the applied transforms of ancestor elements:</p> <pre><code>public static Transform GetAncestorTransforms(this DependencyObject descendant) { TransformGroup transformGroup = new TransformGroup(); DependencyObject dObj = descendant; do { Visual visual = dObj as Visual; if (visual != null) { // determine the current transform by matrix determinants Transform t = VisualTreeHelper.GetTransform(visual); if (t != null) { transformGroup.Children.Add(t); } } dObj = VisualTreeHelper.GetParent(dObj); } while (dObj != null); return transformGroup; } </code></pre> <p>The Adorner draws a round rectangle around the UIElement</p> <pre><code>protected override void OnRender(DrawingContext drawingContext) { var transform = (AdornedItem as DependencyObject).GetAncestorTransforms(); if (transform != null) { drawingContext.PushTransform(transform); } Rect rect = new Rect(AdornedItem.TranslatePoint(new Point(0, 0), AdornedElement), AdornedItem.RenderSize); drawingContext.DrawRoundedRectangle(null, new Pen(Foreground, 2), rect, 2, 2); if (transform != null) { drawingContext.Pop(); } } </code></pre> <p>The code draws the adorner in the correct size (e.g. if it's a scale transform) or it rotates the adorner into the correct angle (if there's a skew/ rotatetransform) but anyway the rectangle is never around the adorned element. it's somewhere beside it. This looks like an offset problem ?</p> <p>(Please note that the problem already occurs when theres just a single transform in the wohole visual tree. When there are more transforms, I'm aware that I might swap the order of the summarized transforms in GetAncestorTransforms().)</p>
 

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