How to render dynamic data in a custom WPF control, such as a line graph?

Question

I'm working on a LineGraph control which consists many DependencyProperties that affect how the control should display its data. For example, the control contains the following properties to affect its axes:

• AxisStroke - Color of the axes.
• AxisThickness - Stroke thickness of the axes.

It also contains properties for display numbers & tick marks

• VerticalTicks - True/False to indicate whether or not ticks appear along the vertical axis
• HorizontalTicks - True/False to indicate whether or not ticks appear along the horizontal axis
• VerticalMin - Minimum value on the vertical axis (numeric)
• VerticalStep - The distance in between each vertical tick
• VerticalMax - Maximum value on the vertical axis (numeric)
• HorizontalMin - Minimum value on the horizontal axis (numeric)
• HorizontalStep - The distance in between each horizontal tick
• HorizontalMax - Maximum value on the horizontal axis (numeric)

And many more properties exist to allow for different line styles on a single graph ( LineColor , LineThickness , DataPointShape , and DataPointIcon to name a few).

My goal is to be able to call out my LineGraph in XAML to insert it into a Window . I would like to be able to specify each of these settings inside the XAML as well, and see the new rendered image of the control in the WPF designer .

Now, given there is a lot of geometric shapes to render on the LineGraph , I though using a Canvas would be a good choice to render the data. Unfortunately, when I'm working in XAML, I cannot perform computations for the locations of shapes based on the control's width & height.

And yes, the shapes' locations must be computed because the data points for the graph are dynamic and the tick-related information is dynamic. Not to mention, I would like to display the actual values along each axis of the LineGraph .

So, I thought I might be able to display this control as if I was doing the rendering in C# code. Other windowing frameworks sometimes provide a Render method that can be used for laying out all of the sub-components.

Doing this, however, doesn't seem possible since WPF relies heavily on XAML for the visual appearance of controls. Also, requiring that the WPF designer must display the LineGraph based on the properties and data specified, it doesn't seem like C# code would solve the problem.

I suppose my questions are these:

How can I render data dynamically inside of a WPF control?

Am I able to specify in C# how my control is rendered, allowing the WPF designer to reflect it?

---

Side Note:
I've done quite a bit of research, but I am only finding information on how to implement more simple types of controls. If you know of any references that contain information on this topic, please feel free to post them in addition to your answers. I will be more than happy to learn how to do this completely.

EDIT: I've created a graph using Excel to elaborate what the LineGraph control might look like if it has correct data and properties.

Answer 1

I will answer this based on my experience on implementing custom built graphing libraries in WIN32, WinForm, WPF, WinCE, WP8+WinRT, ....and even on a FPGA :)

---

It's extremely difficult to implement one from scratch. It may seem easy at first but you will run into a lot of "What should I do if this happens?". For example, in your above graph it seems you got a DataPoint @ (5,100) it graphs it pretty well. But lets say, I add another DataPoint @ (5.000000005, 0). How would you handle that in your code? Would you say that each pixel on the graph represents an exact value on the X-Axis, or does each pixel represent a range of X-Values?

I would recommend that you use an already establish library to do what you want to do unless you need something very specific like lets say you need horizontal cursors on the graph (think Tektronix Oscilloscope) and you need to calculate some values in between the two cursors.. then maybe you need to implement your own custom one or build on top of an open source one.

So, if you are still adamant of creating your own custom control here are answers to your questions.

---

How can I render data dynamically inside of a WPF control?

You can use a WriteableBitmap and create your own primitive drawing library from that. After you're done rendering, set it as the ImageSource of your control. Or you can use WriteableBitmapEx which has GDI like drawing functions already implemented for you.
WriteableBitmapEx CodePlex Page , I also think you can just get it from NuGet as well.
You can also use a <Canvas> and add UI elements to that as well.

---

Am I able to specify in C# how my control is rendered, allowing the WPF designer to reflect it?

This depends on how you create your controls, but yes you can create Properties in your custom control that will appear in the Designer. Allowing you to change it thus updating the display. I would read a lot of tutorials about writing your own custom user control library. They can explain it better than I can in a SO answer. If you implement the properties correctly it should like so.....

---

Full Size Image: http://i.stack.imgur.com/pmevo.png

After changing the Number of Rows from 15 to 10 and the starting Y offset to -1 (thus moving the graph up and making the rows a lot taller)

Full Size Image: http://i.stack.imgur.com/0RKnA.png