Transparent digital clock

• Download demo project - 19.5 Kb
• Download source - 11.5 Kb

Introduction

Clock is a simple program in C++ which shows the current local time in a transparent window. When time changes the window region changes as well using only the area necessary for displaying time. Instead of setting a timer to read time, the program uses a thread which posts a WM_CLOCKTIMETICK message each second.

Brief description

Program displays time in 4 LEDs as shown in the following image:

Each LED consists of 7 lines so we need an array of 4 * 7 = 28 elements to describe each line. Each element shows the starting position of the corresponding line and how this is going to be drawn, horizontally or vertically.

// structure that describes each element

typedef struct _MZDrawObj
{
    int xPos; // x-coordinate

    int yPos; // y-coordinate

    char cType; // 1: horizontaly, 2: verticaly

} MZDrawObj;

// array for describing each line

MZDrawObj m_obj[4][7];

We also need to represent each hour (0 to 23) and minute (0 to 59) with the respective lines that will be drawn. In order to achieve this I use an array of 24 elements (WORD m_objHour[24]) for the first 2 LEDs (hour LEDs) and another one of 60 elements (WORD m_objMin[60]) for the last 2 LEDs (minute LEDs). Each element describes exactly which lines will be drawn (7 bits for each LED).

           0                   0
         *****               *****
        *     *             *     *
      5 *     * 1         5 *     * 1
        *  6  *             *  6  *
         *****               *****
        *     *             *     *
      4 *     * 2         4 *     * 2
        *     *             *     *
         *****               *****
           3                   3  

       1st BYTE            2nd BYTE

• Function InitDrawObj initializes array elements.
• Function DrawObj draws the specified m_obj element.
• Function DrawHour draws the specified m_objHour element (hour LEDs).
• Function DrawMin draws the specified m_objMin element (minute LEDs).
• Function DrawDot draws the separator dot between hour leds and minute leds. It is called twice.
• Function DrawTime does the whole drawing.

Defining window region

Variable HRGN m_hWndRgn defines window region. Function DefineWndRegion reads local time and creates window region. When time changes window region changes as well.

Thread function TimeTickThread posts a message each second which calls OnTimeTick responsible for changing window region and drawing the window.

Using the code

Source code is free for anyone who might find it interested.