CrystalTrackBar: Gradient, Transparent TrackBar that works on ToolStrip as well as Windows Forms.

I'm finally ready to release alpha version 0.66 of Crystal Toolkit that contains the CrystalTrackBar control for Windows Forms and .NET 2.0 Framework. It's a replacement for the TrackBar control that contains many of the same properties (Maximum, Minimum, TickFrequency, Orientation, etc.) with some new features. Before I dive into that list, I'd like to answer the question: "Why replace the TrackBar at all? Doesn't it already work just fine?" It does work great, but I ran into a couple of situations where it wasn't right for my applications.

My first problem with the TrackBar was the visual look that it has when hosted on a ToolStrip (see my earlier article which how to do this using ToolStripControlHost). When the ToolStrip's RenderMode is set to ManagerRenderMode, the background of the control has a nice, smooth gradient effect (depending on the Theme you selected in Windows). But the TrackBar doesn't know anything about the ToolStrip or the RenderMode. It continues to paint its background using the default control color. The picture above is an example of this. Not a pleasing sight for anyone, is it?

I fiddled with the ToolStripControlHosted TrackBar for a while, trying all kinds of hacks to make it work seamlessly. I came to the conclusion that I was going to have to write my own TrackBar control in order to have full authority over the painting. I started playing around with some base classes that would allow me to create controls with gradient backgrounds and color angles. I tried this with my early versions of CrystalTrackBar and liked the results I saw when it was placed on a Form. When placed on a ToolStrip, it was better than what I had before, but still not great. Then I discovered how to make a control's background totally transparent (see my earlier article on my sources for transparent controls). My solution was to put a property in my base class (CrystalGradientControl) called TransparentMode.

When TransparentMode is set to true, the control's background is invisible. When TransparentMode is set to false, the control's background can have a gradient effect (or a single solid color if you set both Color1 and Color2 to the same value). With CrystalTrackBar in TransparentMode, I was able to make it blend in perfectly with a Form that contains a background image. I created a ToolStrip host called CrystalToolStripTrackBar and the result was the same: the transparent background allowed the gradient effect of the RenderMode to be exposed. I decided to set the TickStyle to none on the CrystalToolStripTrackBar by default, because most applications that have a slider on the ToolStrip don't have them.

In order to produce CrystalTrackBar, I had to take full control of all the painting. For the slider bar (or TrackBar as I call it inside the code) and the ticks running next to the slider, I used the TrackBarRenderer class. I started using the TrackBarRenderer class to draw the thumb as well, but ran into a few problems. TrackBarRenderer's methods to draw the thumb take a regular Rectangle structure with integers. In order to make the Thumb position itself correctly above each tick, the coordinates I calculated were floats-so I had to use RectangleF. I decided to create my own bitmaps for the Thumb and an enum called CrystalThumbState to represent different states (Normal, Hover, Pressed, Erasing). CrystalTrackBar's thumb has a light blue glow when you hover over the control and a dark blue outline when you drag it. I'm not the greatest icon artist in the world, and if you care to replace my thumb bitmaps with your own, please do so-just send me a copy (richard at attilan dot com).

It wasn't my initial goal to make a full TrackBar replacement and I don't think I've matched it 100%. However, I didn't feel right releasing even an alpha version without supporting TrackBar's Minimum, Maximum, TickFrequency, TickStyle, and Orientation properties, in addition to supporting the ValueChanged event. CrystalTrackBar has a couple of other minor features. KeyboardControl is a Boolean value that will allow you to turn off keyboard input for the trackbar. By default, if the CrystalTrackBar is horizontal, a few keystrokes (Left, Right, Home, End) can change the values. In vertical mode the keystrokes are Up, Down, Home, End. Some applications use these keystrokes for other operations, so you can turn this off here. TickValues is a list (of integers) representing the tick marks on the CrystalTrackBar. If you have set Minimum to 0, Maximum to 100, and TickFrequency to 10, the TickValues list will be 0, 10, 20, 30, etc., all the way to 100. This could be useful for adding these values to a ComboBox.

You can download CrystalTrackBar in the Downloads section. It comes with full source code and demo programs.