Why does use of pens with dash patterns cause huge (!) performance degredation in WPF custom 2D drawing?

Question

Hope anyone can shed light on this so I can use pens with dash patterns?

I am writing a scrollable chart (a Panel inside ScrollViewer that implements IScrollInfo) in WPF using DrawingVisual's DataContext.DrawX. I have several thousand DrawingVisuals that get scrolled by using TranslateTransform on the Panel that hosts them. I implemented a grid by placing a Panel on top of it and drawing simple horizontal lines from one edge to the other using DataContext.DrawLine(pen, new Point(0, y), new Point(widthOfPanel, y)); //(note: these lines are always static, they never move).

The scroll performance is absolutely insane (i.e. DrawingVisual's are drawn instantly and scrolling is instant). But if I use a Pen that uses dash patterns (see below for example) to draw the grid lines, then scrolling is very jerky and the performance seems to have been decreased by a factor of 100 (an estimate). Can anyone explain why that happens and how I can workaround this?

Example of Pen with dash pattern:

<Pen x:Key="PenUsingDashPatterns" Brush="Black" Thickness="1">
   <Pen.DashStyle >
      <DashStyle Dashes="3, 3" />
   </Pen.DashStyle>
</Pen>

Answer to Josh's question: All freezable resources such as Pens are frozen automatically when they are read from the resource dictionary. — , Feb 12 '09 at 20:35

score 6 · Answer 1 · answered Apr 13 '09 at 16:48

Here's a possible workaround - if you're only drawing horizontal and/or vertical lines you could try creating your Pen with a checker pattern DrawingBrush such as:

  <Pen x:Key="PenUsingDashPatterns" Thickness="1">
        <Pen.Brush>
            <DrawingBrush TileMode="Tile" 
                          Viewport="0 0 6 6" ViewportUnits="Absolute">
                <DrawingBrush.Drawing>
                    <GeometryDrawing Brush="Black">
                        <GeometryDrawing.Geometry>
                            <GeometryGroup>
                                <RectangleGeometry  Rect="0 0 3 3"/>
                                <RectangleGeometry  Rect="3 3 3 3"/>
                            </GeometryGroup>
                        </GeometryDrawing.Geometry>
                    </GeometryDrawing>
                </DrawingBrush.Drawing>
            </DrawingBrush>
        </Pen.Brush>
    </Pen>

Alternatively, you could use different brushes for verical and horizontal lines, or, possibly, an ImageBrush for better performance.

This worked for me. I've replaced my Lines that were using the StrokeDashArray property to use an equivalent of your code. Thanks! — SuperOli, Apr 06 '11 at 19:33
Awesome! The performance in waaay better. Thanks for providing this solution :) — Henrik Carlsson, Jul 05 '11 at 07:06
@SuperOli Could you share any hints of how to convert from Shape.Line to LineGeometry ??? Thanks — isra60, Feb 28 '17 at 08:52

score 3 · Accepted Answer · answered Feb 11 '09 at 18:58

3

Are the pens getting frozen? Freezing drawing objects helps performance a lot.

You could set up a Loaded handler and debug to see if your pens are frozen. If not, Call the Pen.Freeze() button manually on them.

Note that freeze also makes the pens read-only... you will be unable to modify them after you freeze them.

answered Feb 11 '09 at 18:58

Josh G

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It's strange how my bounty went to the only answer that was not helpful. I didn't pick it and don't know to change this. – Apr 18 '09 at 16:36
Sorry my answer wasn't helpful. After the period for the bounty expires, it will automatically assign as the answer the response with the most votes. – Josh G Apr 20 '09 at 12:58

score 3 · Answer 3 · answered Apr 13 '09 at 15:31

3

You should use Perforator to dig deeper into the performance issue. Here's a link to the MSDN site talking about various WPF performance tools. Perforator would probably be the tool that will help you the most, specially in determining if the lines are being drawn using the software renderer (which would be the greatest factor in giving you such bad performance).

If the problem is that they are being drawn in software, you might have to write your own ShaderEffect, but that will probably get tricky fast unless you are familiar with HLSL.

answered Apr 13 '09 at 15:31

Erich Mirabal

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Thanks, but I've tried the WPF performance tools. They are pretty much useless when working with Visuals. I've had more luck with traditional performance tools and debugging WPF source code and my conclusion was that it could have been implemented much more efficiently. But I guess that is the trade off for getting all that productivity. – Oct 05 '09 at 10:58

score 2 · Answer 4 · answered Apr 08 '09 at 14:58

2

Most likely this is because this particular draw operation isn't something that can be delegated to the video card, which would force composition in memory and blitting to the video card.

answered Apr 08 '09 at 14:58

Peter Wone

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Why does use of pens with dash patterns cause huge (!) performance degredation in WPF custom 2D drawing?

4 Answers4

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