Colour preview and picker applet

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• Download Static Linked Executable - 122 Kb

Introduction

This is a simple applet that can be used to preview how various coloured font and background colours interact with each other. It also has the ability to pick colours from anywhere on the screen.

This app is based on Colin Davies' Corner Color Test which, unfortunately, had a few problems when I tried to run it on my Win2000 machine. Rather than bother Colin, who is very busy with his latest project, I thought I would have a go at writing my own version.

Credits

• Colin Davies for the original idea, plus the help and suggestions he gave in developing this app.
• Dr Joseph Newcomer for his CImageButton class.
• Keith Rule for his CMemDC class.
• Various others for suggestions and testing.

Using the Colour applet

Note : All settings are saved in the registry under the key :

HKEY_CURRENT_USER
    \Software
        \PJ Arends
            \Colour
                \Settings

Main Window

Colour Options Dialog

Classes of Interest

CMagnifierWindow class

The CMagnifierWindow class is a simple class that is used by the Colour app to show a magnified portion of the screen. While the magnifier window is on the screen, it will remain centered on the mouse cursor. You can move the cursor, and the magnifier window, around the screen using the mouse or the arrow keys on the keyboard. A left mouse button click, or the 'Enter" or 'Escape' keys will hide the magnifier window from view.

To use the class in one of your own apps, add the files MagnifierWindow.h and MagnifierWindow.cpp to your project. Simply declare an instance of the class in your code, call the Create() member function to create the window, call the ShowMagnifier() function to use the magnifier, and the HideMagnifier() function to stop using it. When the user hides the magnifier window by clicking or using the keyboard, the window will post a user defined message WMU_HIDEMAGNIFIER which is defined in the MagnifierWindow.h header file.

The operation of the magnifier is quite simple. In the ShowMagnifier() function a snapshot is taken of the entire screen and saved in a screen size bitmap that is left selected in a memory device context, and the window is shown using a call to the ShowWindow(SW_SHOW) function. As the window moves around the screen, the portion of the screen that is to be magnified is drawn into the magnifier window using the StretchBlt() function. Then, in the HideMagnifier function, the bitmap and memory device context are destroyed, and the window is hidden with a call to the ShowWindow(SW_HIDE) function.

CMagnifierWindow class member functions

CMagnifierWindow::CMagnifierWindow()

The class constructor initializes the class members but does not create the actual window, you have to call the Create() function to do that. The constructor takes no parameters, and does not return any value.

BOOL CMagnifierWindow::Create (int size, int pixels, CWnd* pParentWnd)

The Create() function creates the actual magnifier window, but leaves it hidden from view. The Create() function returns a nonzero value if it is successful in creating the window, and it returns zero if it fails.

Parameters

• int size - The size of the magnifier window in pixels
• int pixels - The number of pixels to be shown in the magnifier window
• CWnd *pParentWnd - A pointer to the magnifier window's parent window. This is the window that will receive the WMU_HIDEMAGNIFIER message when the user hides the magnifier window

BOOL CMagnifierWindow::ShowMagnifier()

The ShowMagnifier() function shows the magnifier window on the screen. The function returns TRUE on success, and FALSE on failure. The function does not take any parameters

void CMagnifierWindow::HideMagnifier()

The HideMagnifier() function removes the magnifier window from the screen, but it does not destroy it. The function takes no parameters, and does not return any value.

Other classes

While the rest of the classes are nothing special, some people may be interested in some of the functionality.

The CNumEdit class (NumEdit.cpp and NumEdit.h) is a CEdit derived class the limits it's input to decimal or hexadecimal numbers between 0 and 255. The class uses the EN_UPDATE message handler to validate the numbers entered into it.

The CColourSlider class (ColourSlider.cpp and ColourSlider.h) is a simple subclass of a CSliderCtrl that draws a gradient colour in the track bar.

That's it, I hope some of you find this useful.