C# Slider/Trackbar Control using Windows Forms

• Download ColorSliderProject - 1.3 MB
• Download ColorSlider - 0.85 MB

Introduction

ColorSlider is a slider/trackbar control written in C# (Windows Form).

This is an alternative to the standard Microsoft Visual Studio trackbar control which is not so flexible, lacks basic functionalities and is a little poor in design.

The code is a free interpretation of the original code from Michal Brylka published in the site Code Project.
See https://www.codeproject.com/Articles/17395/Owner-drawn-trackbar-slider

The main enhancements brought by this control are:

• A less surface
• The possibility to parametrize the shape of the thumb or to replace it by an image
• Subdivisions added between main divisions
• The text value of the main divisions
• Many colors parametrization added (ticks, bar, elapsed)
• The orientation can be horizontal and vertical (starting from the bottom)

Using the Code

The control is drawn in the overridden event OnPaint, depending on if it is enabled or not, and if the mouse is over it or not.

• If not enabled, the colors are desaturated
• If the mouse is over, the colors are lighten
• Else, the colors are those chosen in the property box

Depending on these colors, the function DrawColorSlider is called and draws everything.

3 rectangles are mainly used to draw the control:

• barRect is used to draw the bar (Elapsed and remaining)
• thumbRect is used to draw the thumb
• elapsedRect is the rectangle for the elapsed bar (the left of the thumb if the orientation is horizontal)

The elapsed bar is composed of 3 single lines (inner, top and bottom), having each its own color:

// Draw horizontal elapsed inner line with "DrawLine" function
// x1 = barRect.X
// y1 = barRect.Y + barRect.Height / 2
// x2 = barRect.X + elapsedRect.Width
// y2 = y1
e.Graphics.DrawLine(new Pen(elapsedInnerColorPaint, 1f), x1, y1, x2, y2);

Top and bottom lines are drawn 1 pixel above or under the inner line. A vertical line of 3 pixels is added at the beginning to improve the 3D effect.

The rest of the bar is also composed of 3 single lines (inner, top and bottom), each having its own color.
A vertical line of 3 pixels is added at the end to improve the 3D effect.

The thumb is drawn according to whether it is an image or not:

• Image: e.Graphics.DrawImage(bmp, thumbRect, srceRect, GraphicsUnit.Pixel);
• Drawn by the control, with a linear gradient, e.Graphics.DrawPath(thumbPen, thumbPath);

The ticks and texts are drawn in two nested loops:

• A first loop from 0 to ScaleDivision for the main graduations and texts
• A nested loop from 0 to ScaleSubDivision for the subdivisions

The offset between each tick is a multiple of W/(nbticks -1) where:

• W is the width of the bar, minus the width of the thumb, in order that when the thumb is at minimum position or maximum position, the graduation coincides with the middle of the thumb
• nbticks is the number of graduations including subdivisions: nbticks = 1 + _scaleDivisions * (_scaleSubDivisions + 1);

Properties

Events

Two events are available:

• ValueChanged
• Scroll

Typical usage of ValueChanged event:

private void colorSlider1_ValueChanged(object sender, EventArgs e)
 {
     label1.Text = colorSlider1.Value.ToString();
 }

Points of Interest

This project was developed with Visual Studio version 2017.

So, as you see, nothing very difficult in this control.
You just have to draw lines and calculate precisely where they start and where they end...

This simple control shows that with a few efforts we can design a control with beautiful effects. The difficulty in reality is not technical, but it consists of choosing the right assortment of colors.