如何只重绘特殊区域？

Question

My English skill is poor because I'm not a native speaker.

I have written an editor that has a visual effect like Highlight. The editor has DrawingControl for representing a visual effect as the following code.

public class HighlightTextBox : TextBox
{
    private DrawingControl renderCanvas;
}

public class DrawingControl : FrameworkElement
{
    private VisualCollection visuals;
    private DrawingVisual visual;

    public DrawingControl()
    {
        visual = new DrawingVisual();
        visuals = new VisualCollection(this);
        visuals.Add(visual);
    }

    public DrawingContext GetContext()
    {
        return visual.RenderOpen();
    }

    protected override int VisualChildrenCount
    {
        get { return visuals.Count; }
    }

    protected override Visual GetVisualChild(int index)
    {
        if (index < 0 || index >= visuals.Count)
            throw new ArgumentOutOfRangeException();
        return visuals[index];
    }
}

If a user input a character on the editor then the TextChanged event is called. And after that, the OnRender function is called by calling InvalidateVisual function.

TextChanged(s,e)
{
    InvalidateVisual();
}

Then all text is drawn that has a visual effect by using DrawingContext in the DrawingControl.

protected override void OnRender(DrawingContext drawingContext)
{
    if (this.bSingleLineChanged)
    {
        this.SingleLineChangedRender(drawingContext);
        this.bSingleLineChanged = false;
        return;
    }
    else
        this.AllRender(drawingContext);
}

private void AllRender(DrawingContext drawingContext)
{
    // Calculate drawing position, texts, etc...

    var dc = this.renderCanvas.GetContext();

    // Here draw texts

    dc.Close();
    base.OnRender(drawingContext);
}

As a result, drawing process success when all text is repainted but the way take a lot of time. To shorten a drawing time, I tried to repaint only an updated part. The part drawing process is defined in the SingleLineChangedRender function. Also the logic of the function alike with an AllRender function.

Now I would explain a problem. I calculate an updated part and have written logic in the SingleLineChangedRender function. But when is called a GetContext function in the SingleLineChangedRender function all drawn context is erased.

private void SingleLineChangedRender(DrawingContext drawingContext)
{
    // I think that here all drawn contexts are erased.
    var dc = this.renderCanvas.GetContext();

    // Here draw texts

    dc.Close();    
    base.OnRender(drawingContext);
}

I want to repaint only an updated part but I can't do it because all contexts is erased when the GetContext function is called.

I would like to seek your advice to solve this problem.

Thank you for reading.

Answer 1

I follow your advice and I solved this problem by updating DrawingControl class.

I updated the TextViewer class as a container of DrawingContext.

As a result, the class has formed the following.

public class TextViewer : FrameworkElement
{
    // For highlighting of the selected line.
    private DrawingVisual selectionLineAppearance = new DrawingVisual();

    // For highlighting tokens of the lines.
    private VisualCollection lines;

    protected override int VisualChildrenCount
    {
        // selectionLineAppearance + lines
        get { return 1+lines.Count; }
    }

    protected override Visual GetVisualChild(int index)
    {
        if (index < 0 || index >= VisualChildrenCount)
            throw new ArgumentOutOfRangeException();

        if (index == 0) return this.selectionLineAppearance;
        return lines[index-1];
    }

    // logices
    ...

}

Now, Editor can repaint only an updated part. Addition can paint the appearance of the selected line.

Thank you for your advice.