Win8ProgressRing Control

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Introduction

This short article presents a control, named Win8ProgressRing, that mimics the Windows 8 Progress Ring.

Only a brief discussion of its implementation will be provided. In the following discussions, properties that are specified by the developer are displayed in BoldMixedCase text. Variables, used internally by the software are displayed in italicized_lowercase text.

Visual Properties

The Win8ProgressRing control has two properties that form the user's visual image. In the figure to the right, the control's boundary is drawn in red.

The developer specifies the control's top-left corner by dragging the control from the ToolBox to a position on the form. This position becomes ( 0, 0 ) in the control's graphic environment. The developer specifies the control_height by either dragging the control's resizing handles or by specifying the Control_Height property. The control_width is set equal to the control_height.

The indicator color defaults to white. To change the indicator color, the developer specifies the new color through the Indicator_Color property.

The control's background color is transparent and cannot be changed.

Control Properties

The Win8ProgressRing control has the following properties available to the developer:

// ********************* adjust_control_dimensions_from_height

void adjust_control_dimensions_from_height ( int new_height )
    {

    indicator_radius = round ( ( double ) new_height / 
                               ( double ) SIZE_FACTOR );
    indicator_diameter = 2 * indicator_radius;

    control_height = SIZE_FACTOR * indicator_radius;
    control_width = control_height;

    outer_radius = control_height / 2;
    inner_radius = outer_radius - indicator_diameter;

    indicator_center_radius = inner_radius + 
                              indicator_radius;

    this.Height = control_height;
    this.Width = control_width;
    }

The Pulse method is used to rotate the indicators once each time it is invoked. Its signature is:

public void Pulse ( )

Implementation

The Win8ProgressRing control is a User-Drawn Control. Parts of the control are drawn when the control's OnPaint method is invoked.

The control's graphic is made up of two distinct graphic images: the background graphic and the indicator graphic.

Once drawn, the background graphic does not need to be redrawn unless Control_Height is changed. The indicator graphic must be redrawn when the background graphic is redrawn; when the animation changes the indicators' positions; or when the indicator color changes.

The control is made up of six circular indicators that travel around the center of the control. Initially the indicators are grouped together starting at 90 degrees.

Note

The control uses Windows coordinates with the x-axis values increasing to the right; y-axis values increasing downward; and angles measured clockwise from the x-axis.

Starting with the most clockwise indicator, it is moved 11.25 degrees clockwise. If the indicator ends up in the fast movement area of the control, on the next pass, it will be moved some multiple of 11.25 degrees.

The angular advance (11.25) was derived from the desire to have eight indicators displayed in a quadrant. This results in 32 indicators around the control. Dividing 360 by 32 yields the advance of 11.25 degrees.

Because the trigonometric functions Sine and Cosine are invoked at each indicator advance, two tables are generated at initialization that contain 1440 values of the trigonometric functions in increments of 0.25 degrees.

Each of the six indicators is an instance of the Indicator class.

// *********************************************** class Indicator

public class Indicator
    {
    double  degrees = 0.0;
    double  fast = 1.0;

    // ************************************************* Indicator

    public Indicator ( )
        {

        Degrees = 0.0;
        Fast = 1.0;
        }

    // ************************************************* Indicator

    public Indicator ( double  degrees )
        {

        Degrees = degrees;
        Fast = 1.0;
        }

    // *************************************************** Degrees

    public double Degrees
        {

        get
            {
            return ( degrees );
            }
        set
            {
            degrees = value;
            }
        }

    // ****************************************************** Fast

    public double Fast
        {

        get
            {
            return ( fast );
            }
        set
            {
            fast = value;
            }
        }

    } // class Indicator

Finally, draw_indicator_graphic is invoked each time the interval timer raises the elapsed event.

// ************************************ draw_indicator_graphic

void draw_indicator_graphic (  Graphics graphics )
    {
    Brush       brush = new SolidBrush ( Indicator_Color );
    Rectangle   rectangle = new Rectangle ( );

    for ( int i = ( MAXIMUM_INDICATORS - 1 );
              ( i >= 0 );
              i-- )
        {
        double  degrees = indicators [ i ].Degrees;
        int     dx;
        int     dy;

        if ( degrees < 0.0 )
            {
            degrees += 360.0;
            }

        dx = round ( ( double ) indicator_center_radius *
                     cos ( degrees ) ) +
             indicator_center_radius;
        dy = indicator_center_radius -
             round ( ( double ) indicator_center_radius *
                     sin ( degrees ) );

        rectangle.Location = new Point ( dx, dy );
        rectangle.Size = new Size ( indicator_diameter,
                                    indicator_diameter );
        graphics.FillEllipse ( brush, rectangle );

        degrees -= ( double ) indicators [ i ].Fast *
                   INDICATOR_OFFSET;

        if ( indicators [ i ].Fast > 1.0 )
            {
            indicators [ i ].Fast += 0.25;
            }

        if ( degrees < 0.0 )
            {
            indicators [ i ].Fast = 1.25;
            }
        else if ( degrees < START_AT )
            {
            indicators [ i ].Fast = 1.0;
            }

        indicators [ i ].Degrees = degrees;
        }

    brush.Dispose ( );
    }

Graphics Buffer

The GraphicsBuffer class contains an off-screen bitmap used to draw graphic objects without flicker. Although .Net provides a Double Buffered Graphics capability, it is overkill for the Win8ProgressRing control.

GraphicsBuffer has been included within the control.

Conclusion

This article has presented a control that mimics the Windows 8 Progress Ring.

References

• Add Items to the Toolbox
• Double Buffered Graphics
• Graphics
• Implementing Events
• Raising an Event
• Rounding
• User-Drawn Controls

Development Environment

Win8ProgressRing control was developed in the following environment:

History