Question

I am drawing at dc (DrawingContext) of a Grid like this:

dc.DrawImage(_imageSource, new Rect(x, y, width, height);

But, what if I wanted to rotate the image I am drawing on drawing context?

I know I can push effect to drawing context, but, it will affect all the drawings, while I want to rotate only drawing of _imageSource.

Any idea?

Answer 1

You could push a RotateTransform before drawing the image, and immediately pop the transform after drawing.

var transform = new RotateTransform(...);
dc.PushTransform(transform);
dc.DrawImage(_imageSource, new Rect(x, y, width, height));
dc.Pop();

Alternatively you could create an ImageDrawing, add it to a DrawingGroup (which has a Transform property), and then draw the DrawingGroup:

var drawingGroup = new DrawingGroup();
drawingGroup.Transform = new RotateTransform(...);
drawingGroup.Children.Add(new ImageDrawing(_imageSource, new Rect(x, y, width, height)));
dc.DrawDrawing(drawingGroup);

All the DrawingContext.Draw… methods actually create and draw the appropriate Drawing objects.

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Instead of continuously redrawing everything in an overridden OnRender() method you could also do the following:

• Create a DrawingVisual as a container for your drawings. See Using DrawingVisual Objects about how to do that.

• Create a DrawingGroup with an ImageDrawing as shown above and draw the DrawingGroup once into the DrawingContext provided by DrawingVisual.RenderOpen.

• Use a MatrixTransform or a TransformGroup for the complete image transformation, i.e. translation and rotation. Set the DrawingGroup.Transform property to this transform (instead of RotateTransform only as shown above).

• When an image’s position or rotation angle changes, only change the related transform. Redrawing is not necessary.