Question

I am developping an application where I need to draw a graph on the screen.
For this purpose, I use a Canvas and I put Controls on it.

An example of such a draw as shown in the app can be found here :
http://free0.hiboox.com/images/1610/d82e0b7cc3521071ede601d3542c7bc5.png

It works fine for simple graphs, but I also want to be able to draw very large graphs (hundreds of nodes). And when I try to draw a very large graph, it takes a LOT of time to render.

My problem is that the code is not optimized at all, I just wanted it to work. Until now, I have a Canvas on the one hand, and multiple Controls on the other hands. Actually, circles and lines are listed in collections, and for each item of these collections, I use a ControlTemplate, defining a red circle, a black circle, a line, etc.

Here is an example, the definition of a graph circle :

<!--
STYLE : DISPLAY DATA NODE
-->
<Style TargetType="{x:Type flow.elements:DisplayNode}">
    <Setter Property="Canvas.Left" Value="{Binding X, RelativeSource={RelativeSource Self}}" />
    <Setter Property="Canvas.Top" Value="{Binding Y, RelativeSource={RelativeSource Self}}" />
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type flow.elements:DisplayNode}">

                <!--TEMPLATE-->
                <Grid x:Name="grid" Margin="-30,-30,0,0">
                    <Ellipse x:Name="selectionEllipse" StrokeThickness="0" Width="60"
                            Height="60" Opacity="0" IsHitTestVisible="False">
                        <Ellipse.Fill>
                            <RadialGradientBrush>
                                <GradientStop Color="Black" Offset="0.398" />
                                <GradientStop Offset="1" />
                            </RadialGradientBrush>
                        </Ellipse.Fill>
                    </Ellipse>
                    <Ellipse Stroke="Black" Width="30" Height="30" x:Name="ellipse">
                        <Ellipse.Fill>
                            <LinearGradientBrush EndPoint="0,1">
                                <GradientStop Offset="0" Color="White" />
                                <GradientStop Offset="1.5" Color="LightGray" />
                            </LinearGradientBrush>
                        </Ellipse.Fill>
                    </Ellipse>
                    <TextBlock x:Name="tblock"
                            Text="{Binding NodeName, RelativeSource={RelativeSource Mode=TemplatedParent}}"
                            Foreground="Black" VerticalAlignment="Center"
                            HorizontalAlignment="Center" FontSize="10.667" />
                </Grid>

                <!--TRIGGERS-->
                <ControlTemplate.Triggers>
                    <!--DATAINPUT-->
                    <MultiTrigger>
                        <MultiTrigger.Conditions>
                            <Condition Property="SkinMode" Value="NODETYPE" />
                            <Condition Property="NodeType" Value="DATAINPUT" />
                        </MultiTrigger.Conditions>
                        <Setter TargetName="tblock" Property="Foreground" Value="White" />
                        <Setter TargetName="ellipse" Property="Fill">
                            <Setter.Value>
                                <LinearGradientBrush EndPoint="0,1">
                                    <GradientStop Offset="-0.5" Color="White" />
                                    <GradientStop Offset="1" Color="Black" />
                                </LinearGradientBrush>
                            </Setter.Value>
                        </Setter>
                    </MultiTrigger>

                    <!--DATAOUTPUT-->
                    <MultiTrigger>
                        <MultiTrigger.Conditions>
                            <Condition Property="SkinMode" Value="NODETYPE" />
                            <Condition Property="NodeType" Value="DATAOUTPUT" />
                        </MultiTrigger.Conditions>
                        <Setter TargetName="tblock" Property="Foreground" Value="White" />
                        <Setter TargetName="ellipse" Property="Fill">
                            <Setter.Value>
                                <LinearGradientBrush EndPoint="0,1">
                                    <GradientStop Offset="-0.5" Color="White" />
                                    <GradientStop Offset="1" Color="Black" />
                                </LinearGradientBrush>
                            </Setter.Value>
                        </Setter>
                    </MultiTrigger>

                    ....... THERE IS A TOTAL OF 7 MULTITRIGGERS .......

                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

Also, the lines are drawn using the Line Control.

<!--
STYLE : DISPLAY LINK
-->
<Style TargetType="{x:Type flow.elements:DisplayLink}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type flow.elements:DisplayLink}">

                <!--TEMPLATE-->
                <Line X1="{Binding X1, RelativeSource={RelativeSource TemplatedParent}}"
                        X2="{Binding X2, RelativeSource={RelativeSource TemplatedParent}}"
                        Y1="{Binding Y1, RelativeSource={RelativeSource TemplatedParent}}"
                        Y2="{Binding Y2, RelativeSource={RelativeSource TemplatedParent}}"
                        Stroke="Gray" StrokeThickness="2" x:Name="line" />

                <!--TRIGGERS-->
                <ControlTemplate.Triggers>
                    <!--BRANCH : ASSERTION-->
                    <MultiTrigger>
                        <MultiTrigger.Conditions>
                            <Condition Property="SkinMode" Value="BRANCHTYPE" />
                            <Condition Property="BranchType" Value="ASSERTION" />
                        </MultiTrigger.Conditions>
                        <Setter TargetName="line" Property="Stroke" Value="#E0E0E0" />
                    </MultiTrigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

So, I need your advices. How can I drastically improve the rendering performances ? Should I define each MultiTrigger circle rendering possibility in its own ControlTemplate instead ? Is there a better line drawing technique ?

Should I open a DrawingContext and draw everything in one control, instead of having hundreds of controls ?

Answer 1

I see this a lot, and I always have the same answer. That’s what happens when you build graphics. Don’t build graphics, draw graphics. In other words, don’t create a lot of data structure (lots of controls) over and above the application data. Rather, have a Paint event handler that can paint by means of DrawLine, DrawEllipse, etc.

This is a specific instance of the dictum Be a Data-Hater.

Only if you know you have a requirement to be able to respond to mouse contacts on the drawn objects does it make sense to make some kinds of objects, and even then, possibly not.

If rendering causes a lot of flashing because you have so many objects that it takes a noticeable time to render them, try painting to a memory bitmap, and copying that to the screen. Make sure that the pre-paint event doesn’t clear the screen. That’s what I do, and it always looks good.

Added: I realize you can’t always avoid managing a lot of controls, so I’ve got a strategy for that. For example, I often have to write UI dialogs where the content in terms of controls dynamically changes a lot as the underlying application data changes. The standard well-known ways for handling this I find crude, hard to code, and error-prone. Luckily I stumbled on what I think is a much better way, dynamic dialogs. I don’t claim it’s for the faint-of-heart. I do claim it saves an order of magnitude of code, works like a clock, and takes off my hands the business of managing controls, binding, and all that event hoo-haw.