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A Fine-looking Segmented LED Control

, 12 May 2008
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This article describes an approach to constructing a segmented LED displayer
Screenshot - screen_shot.png

Introduction

This article describes an approach to constructing a cool segmented LED displayer that is similar to the LEDs used in alarm clocks and industry monitors. This control can be used to display time, numerical values and even some English characters. I hope it will be helpful in programs such as hardware simulators.

Background

In this section, I would like to give a brief introduction to the ideas behind this control. In a 7-segment LED displayer, one character is composed of at most 7 segments, as in the picture shown below.

Figure 1 - 7 segments

Figure 1: Segmented character

Each segment has the following properties: the width of the segment, the bevel rate of the corners in the segment and the interval between segments.

Figure 2 - 1 segment

Figure 2: Properties of each segment

If we mark those 7 segments with numbers, as the picture shows in Figure 1, then we can use indices to represent different characters. For example, the character "1" can be represented as (2, 3) and the character "5" can be represented as (1, 6, 7, 3, 4). To draw the whole scene, we should first calculate the bound rectangles where a certain character is drawn. Then the segments in each specified bound rectangle should be drawn. The algorithm for drawing a 7-segmented LED character in a specified bound rectangle is shown in Figure 3.

Figure 3 - Algorithm

Figure 3: Drawing one character

Using the code

This control is quite easy to use. Just drag it from the toolbox to your form in design mode. Then adjust its provided properties in the designer or at runtime to modify its appearance. The properties are listed in the table below:

BorderWidth int Get or set the width of the border around the control.
BorderColor System.Color Get or set the color of the border around the control.
HighlightOpaque byte Get or set the opaque value of the highlight. 0 implies that the highlight will end transparent, while 100 implies that the highlight will keep its transparency from the beginning.
ShowHighlight bool Get or set a value indicating whether to show the highlight area on the control. If it is set to false, the value of the HighlightOpaque property is ignored.
CornerRadius int Get or set the corner radius for the control. If RoundCorner equals false, the value of this property is ignored. The valid value is from 1 to 10.
GradientBackground bool Get or set a value indicating whether the background was filled in gradient colors.
BackColor_1 System.Color Get or set the first background color. If GradientBackground equals true, this color will be the color at the top of the background rectangle. Otherwise, this color will be the solid background color.
BackColor_2 System.Color Get or set the second background color. If GradientBackground equals true, this color will be the color at the bottom of the background rectangle. Otherwise, this color will be ignored.
RoundCorner bool Get or set the border style. If it is true, the border of the control will be a round rectangle. Otherwise, the border is a normal rectangle.
SegmentIntervalRatio int Get or set the segment-interval ratio. The larger this value is, the wider the gaps between segments are.
TextAlignment Alignment Get or set the alignment style of the text.
SegmentWidthRatio int Get or set the segment-width ratio. The larger this value is, the wider the segments are.
TotalCharCount int Get or set the total number of characters to display. If the number of characters contained in the displaying text is larger than this value, the displaying character will be truncated.
BevelRate float Get or set the bevel rate of each segment. Please refer to Figure 2 for further information.
FadedColor System.Color Get or set the color of faded background characters.
Text string Get or set the text of the control.

Points of Interest

A control at presentation level may do lots of painting. Most of the time, the control has to be repainted when one of its properties is changed. This may cause multiple invalidating if several properties of the control are changed in quick succession. In order to avoid multiple painting, we can implement the ISupportInitialize interface in our control. First, we set a member variable in the BeginInit() method.

private bool m_bIsInitializing = false;
void ISupportInitialize.BeginInit()
{
    m_bIsInitializing = true;
}

Then we rewrite our properties in the following manner:

public Color FadedColor
{
    get
    {
        return m_colFadedColor;
    }
    set
    {
        if (m_colFadedColor == value)
        return;
        m_colFadedColor = value;
        // check if the control is in initializing mode
        if (!m_bIsInitializing)
        {
            Invalidate();
        }
    }
}

At last, in the EndInit() method, we turn off the initialization mode and repaint the control.

void ISupportInitialize.EndInit()
{
    m_bIsInitializing = false;
    Invalidate();
}

Now we can use batch initialization to prevent successive painting of the control.

((System.ComponentModel.ISupportInitialize)mycontrol).BeginInit();
mycontrol.BackColor = System.Drawing.Color.Transparent;
mycontrol.BackColor_1 = System.Drawing.Color.Black;
mycontrol.BackColor_2 = System.Drawing.Color.Transparent;
mycontrol.BevelRate = 0.5F;
mycontrol.BorderColor = System.Drawing.Color.White;
mycontrol.FadedColor = System.Drawing.Color.Black;
((System.ComponentModel.ISupportInitialize)mycontrol).EndInit();

History

  • 15th July, 2007 -- Original version posted
  • 20th July, 2007 -- Downloads updated
  • 7th May, 2008 -- Downloads updated
    1. User can now turn on smooth drawing mode to make the control look better
    2. Italic text style supported
    3. Bug fixed: The bottom and right bounds are invisible if the bound rectangle is a regular one
  • 12th May, 2008 -- Downloads updated
    1. The user can copy text on the control when the control got focus.
    2. The color of border will change (Defined by user) when the control got and lost focus.
    3. Bug fixed: the anti-alias effect will disappear when the bound is a regulare rect.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Liu Xia
Software Developer
China China
A guy who is a software developer now and hopes to become a Chief Software Architect in the future Smile | :) . Now study in Beijing University of Aeronautics & Astronautics for the master's degree.

Comments and Discussions

 
GeneralMy vote of 5 PinmemberSougata Das8-Mar-13 22:06 
GeneralMy vote of 5 Pinmemberspidergeuse7-Jan-13 4:20 
GeneralMy vote of 5 Pinmemberezekjh27-Apr-11 10:32 
GeneralMy vote of 5 PinmemberAntoine Megens13-Mar-11 6:44 
GeneralThanx great control PinmemberPoul_L5-Nov-10 7:18 
GeneralGreat control! Pinmemberblandwehr13-Nov-08 7:10 
GeneralThis is great PinmemberNicholas Piasecki28-Aug-08 7:52 
GeneralLastest code on CodePlex PinmemberLiu Xia10-May-08 22:12 
GeneralBut it's user hostile! PinmemberPIEBALDconsult8-May-08 13:58 
GeneralRe: But it's user hostile! PinmemberLiu Xia8-May-08 21:45 
GeneralRe: But it's user hostile! PinmemberPIEBALDconsult9-May-08 12:28 
GeneralRe: But it's user hostile! PinmemberLiu Xia9-May-08 17:55 
AnswerRe: But it's user hostile! PinmemberLiu Xia9-May-08 19:10 
GeneralRe: But it's user hostile! PinmemberBruce Munck11-Jul-08 2:18 
GeneralSome letters don't render PinmemberManster8-May-08 11:39 
GeneralRe: Some letters don't render PinmemberLiu Xia8-May-08 21:43 
QuestionPassword? PinmemberKnightRohan11-Jan-08 1:34 
AnswerRe: Password? PinmemberLiu Xia30-Jan-08 15:10 
Generalsuperb Pinmembererdm7-Dec-07 0:48 
GeneralGreat documentation PinmemberMAEI29-Nov-07 12:16 
GeneralBUG in setter of Text PinmemberKenGuru4-Sep-07 2:54 
GeneralRe: BUG in setter of Text PinmemberLiu Xia7-Sep-07 18:01 
Generalawesome PinmemberAntom1-Sep-07 13:50 
GeneralVery Nice PinmemberSpiveyC#23-Aug-07 4:59 
GeneralDefine char with table PinmemberNicolaBitonto26-Jul-07 17:59 
GeneralRe: Define char with table PinmemberYouMiss27-Nov-07 14:52 
GeneralRe: Define char with table Pinmemberjinfd12-May-08 7:55 
GeneralLED Control Pinmembermoegoe24-Jul-07 2:17 
GeneralRe: LED Control PinmemberLiu Xia27-Jul-07 1:08 
GeneralGood work...! PinmemberChamadness24-Jul-07 0:35 
GeneralGood work! PinmemberKhazbak23-Jul-07 21:09 
GeneralReduce computation PinmemberHoria Tudosie23-Jul-07 14:45 
GeneralRe: Reduce computation PinmemberLiu Xia27-Jul-07 0:59 
GeneralUpdated version PinmemberLiu Xia19-Jul-07 17:56 
GeneralVery Slick PinmemberPaul Conrad17-Jul-07 19:20 
GeneralRe: Very Slick PinmemberLiu Xia17-Jul-07 23:07 
GeneralOptimisation Technique PinmemberEd.Poore17-Jul-07 10:47 
GeneralRe: Optimisation Technique [modified] PinmemberLiu Xia17-Jul-07 15:59 
GeneralRe: Optimisation Technique Pinmembersermit24-Dec-07 22:00 

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