Creating a 'Progress Cursor'

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Introduction

This article explains how we can customize the cursor to display a circular progress bar.

Class diagram

Using the code

Using the code is pretty simple, as you can see in 1-1.

var progressCursor = Van.Parys.Windows.Forms.CursorHelper.StartProgressCursor(100);

for (int i = 0; i < 100; i++)
{
 progressCursor.IncrementTo(i);

 //do some work
}

progressCursor.End();

1-1 Basic usage of ProgressCursor

The library also has some points of extensibility, by handling the 'EventHandler<CursorPaintEventArgs> CustomDrawCursor' event. By handling this event, the developer can choose to extend the default behaviour by running the DrawDefault method on the CursorPaintEventArgs instance (1-2).

...
progressCursor.CustomDrawCursor += progressCursor_CustomDrawCursor;
...

void progressCursor_CustomDrawCursor(object sender, 
                    ProgressCursor.CursorPaintEventArgs e)
{
	e.DrawDefault();
	
	//add text to the default drawn cursor
	e.Graphics.DrawString("Test", 
	           SystemFonts.DefaultFont, Brushes.Black, 0,0);
	
	//set Handled to true, or else nothing will happen,
	//and default painting is done
	e.Handled = true;
}

1-2 ProgressCursor extension using events

IProgressCursor also implements IDisposable, which makes the 'using' statement valid on this interface. The advantage is that no custom exception handling has to be done to ensure the End() method is called on the ProgressCursor. An example of the usage is found in 1-3.

using (var progressCursor = CursorHelper.StartProgressCursor(100))
{
    for (int i = 0; i < 100; i++)
    {
        progressCursor.IncrementTo(i);

        //simulate some work
    }
}

1-3 ProgressCursor implements IDisposable

Why implement IDisposable

A classic usage of the default cursor classes would be like this:

private void DoStuff()
{
    Cursor.Current = Cursors.WaitCursor;

    try
    {
        //do heavy duty stuff here...
    }
    finally 
    {
        Cursor.Current = Cursors.Default;
    }
}

If one wouldn't implement the cursor change like this, the cursor could 'hang' and stay 'WaitCursor'. To avoid this Try Finally coding style, I implemented IDisposable on the IProgressCursor like this (2-2):

public ProgressCursor(Cursor originalCursor)
{
    OriginalCursor = originalCursor;
}

~ProgressCursor()
{
    Dispose();
}

public void Dispose()
{
    End();
}

public void End()
{
    Cursor.Current = OriginalCursor;
}

2-2 Classic sample of Cursor usage

How it works

Creating a custom cursor

Basically, all the 'heavy lifting' is done by two imported user32.dll methods (1-3). These can be found in the class UnManagedMethodWrapper (what would be the right name for this class?).

public sealed class UnManagedMethodWrapper
{
	[DllImport("user32.dll")]
	public static extern IntPtr CreateIconIndirect(ref IconInfo iconInfo);

	[DllImport("user32.dll")]
	[return: MarshalAs(UnmanagedType.Bool)]
	public static extern bool GetIconInfo(IntPtr iconHandle, ref IconInfo iconInfo);
}

1-3 P/Invoke methods

These methods are called in CreateCursor (1-4):

private Cursor CreateCursor(Bitmap bmp, Point hotSpot)
{
	//gets the 'icon-handle' of the bitmap
	//(~.net equivalent of bmp as Icon)
	IntPtr iconHandle = bmp.GetHicon();
	IconInfo iconInfo = new IconInfo();
	
	//fill the IconInfo structure with data from the iconHandle
	UnManagedMethodWrapper.GetIconInfo(iconHandle, ref iconInfo);
	
	//set hotspot coordinates
	iconInfo.xHotspot = hotSpot.X;
	iconInfo.yHotspot = hotSpot.Y;
	
	//indicate that this is a cursor, not an icon
	iconInfo.fIcon = false;
	
	//actually create the cursor
	iconHandle = 
	  UnManagedMethodWrapper.CreateIconIndirect(ref iconInfo);
	
	//return managed Cursor object
	return new Cursor(iconHandle);
}

1-4 Cursor magic!

MSDN documentation:

Circular progress cursor drawing

int fontEmSize = 7;

var totalWidth = (int) Graphics.VisibleClipBounds.Width;
var totalHeight = (int) Graphics.VisibleClipBounds.Height;
int margin_all = 2;
var band_width = (int) (totalWidth*0.1887);

int workspaceWidth = totalWidth - (margin_all*2);
int workspaceHeight = totalHeight - (margin_all*2);
var workspaceSize = new Size(workspaceWidth, workspaceHeight);

var upperLeftWorkspacePoint = new Point(margin_all, margin_all);
var upperLeftInnerEllipsePoint = new Point(upperLeftWorkspacePoint.X + band_width, 
                                 upperLeftWorkspacePoint.Y + band_width);

var innerEllipseSize = new Size(((totalWidth/2) - upperLeftInnerEllipsePoint.X)*2, 
            ((totalWidth/2) - upperLeftInnerEllipsePoint.Y)*2);

var outerEllipseRectangle = 
    new Rectangle(upperLeftWorkspacePoint, workspaceSize);
var innerEllipseRectangle = 
    new Rectangle(upperLeftInnerEllipsePoint, innerEllipseSize);

double valueMaxRatio = (Value/Max);
var sweepAngle = (int) (valueMaxRatio*360);

var defaultFont = new Font(SystemFonts.DefaultFont.FontFamily, 
                           fontEmSize, FontStyle.Regular);
string format = string.Format("{0:00}", (int) (valueMaxRatio*100));
SizeF measureString = Graphics.MeasureString(format, defaultFont);
var textPoint = new PointF(upperLeftInnerEllipsePoint.X + 
  ((innerEllipseSize.Width - measureString.Width)/2), 
    upperLeftInnerEllipsePoint.Y + 
    ((innerEllipseSize.Height - measureString.Height)/2));

Graphics.Clear(Color.Transparent);

Graphics.DrawEllipse(BorderPen, outerEllipseRectangle);
Graphics.FillPie(FillPen, outerEllipseRectangle, 0, sweepAngle);

Graphics.FillEllipse(new SolidBrush(Color.White), innerEllipseRectangle);
Graphics.DrawEllipse(BorderPen, innerEllipseRectangle);

Graphics.DrawString(format, defaultFont, FillPen, textPoint);