Environment: VC6 SP4
When developing Web pages or graphics, we frequently need a tool that will give us the RGB value of the color of a particular region in some other application’s window. An example could be that you need to know the background color of a JPG image so that you can use the same color for the background of the Web page on which you will display the image. ColorFinder comes in handy exactly for this. You can use this tool to pick the color from any pixel on the Desktop.
How to Use the Tool
To get the color value, left-click on the dropper icon and, while keeping the left mouse button pressed down, move it over the Desktop. As the mouse moves, ColorFinder shows the color under the mouse pointer and at the same time it displays the pointer coordinates and the value of the color in decimal, hex, and HTML color formats. When the mouse pointer is over the color you want to select, release the mouse button. Then, using the buttons labeled “>” on the right of any of the text boxes displaying the color value, copy that value to the Clipboard.
By default, the tool is always on top of all the application. This allows you to see the color under the mouse pointer as you move the pointer over the Desktop. You can disable this behavior by unchecking the “Always on top” menu option in the application’s system menu.
Using the Code
The source files CButtonSK.h, CButtonSK.cpp, CUrl.h, and Curl.cpp are not directly relevant for this application.
CButtonSK is used for skinning buttons and is used for the copy buttons (labeled with ‘>’).
Curl is used in the About box to display URLs that behave identically to the URLs inside a browser.
The class associated with the main dialog is
CColorFinderDlg and it is defined and implemented in the ColorFinderDlg.h and ColorFinderDlg.cpp files.
In the constructor for this class, the icon and cursor for the dropper are loaded and the
m_bTracking variable is set to
false. The current color
m_colCurrent is set to black.
CColorFinderDlg::CColorFinderDlg(CWnd* pParent /*=NULL*/)
: CDialog(CColorFinderDlg::IDD, pParent)
m_bTracking = false;
m_hCursor = AfxGetApp()->LoadCursor(IDC_DROPPER);
m_hDropperIcon = AfxGetApp()->LoadIcon(IDI_DROPPER);
m_colCurrent = RGB(0,0,0);
To get the color, three Windows messages—
WM_LBUTTONUP—have been used.
When the message handler for
WM_LBUTTONDOWN is called, the handler verifies that the location of the mouse button down is inside the rectangle for the static control that displays the dropper icon. It then sets the mouse tracking flag
m_bTracking and captures the mouse so that all subsequent mouse move messages are sent to the window for
CColorFinderDlg. The handler also changes the mouse cursor to that of the dropper and hides the dropper icon on the dialog. This gives an impression that the dropper is picked up from the dialog’s window.
void CColorFinderDlg::OnLButtonDown(UINT nFlags, CPoint point)
if (PtInRect(&rect, point))
m_bTracking = true;
The handler for the
WM_MOUSEMOVE first verifies that the mouse is being tracked, i.e., the mouse left button is currently down. It does that by using the
m_bTracking variable set in
OnLButtonDown. The current mouse pointer location is obtained using the Win32 API
GetCursorPos. To get the color under the mouse pointer, first a handle to the Desktop device context is obtained using the API
GetDCEx . This handle is then converted to a CDC class pointer by using
CDC::FromHandle. Then, the color is retrieved by using the CDC method
void CColorFinderDlg::OnMouseMove(UINT nFlags, CPoint point)
// Get the mouse pointer position and display it
str.Format (“%d, %d”, pt.x, pt.y);
// Get the device context of the desktop and from it get the
// color of the pixel at the current mouse pointer position
CDC *pDesktopDC = CDC::FromHandle ( ::GetDCEx(NULL, NULL, 0));
m_colCurrent = pDesktopDC->GetPixel(pt);
// Break the color into the RGB components
BYTE rVal = GetRValue(m_colCurrent);
BYTE gVal = GetGValue(m_colCurrent);
BYTE bVal = GetBValue(m_colCurrent);
// Display the pixel color in different formats
str.Format(“%02X, %02X, %02X”, rVal, gVal, bVal);
str.Format(“%d, %d, %d”, rVal, gVal, bVal);
str.Format(“#%02X%02X%02X”, rVal, gVal, bVal);
// Show the color in the static control
CDC *pSDC = m_statCol.GetDC();
In the handler for the
WM_LBUTTONUP, the mouse capture is released and the
m_bTracking flag is cleared. The dropper icon on the dialog is also restored.
void CColorFinderDlg::OnLButtonUp(UINT nFlags, CPoint point)
m_bTracking = false;
Points of Interest
The color displayed in the
m_statCol is not updated with the
The tool gives the actual RGB value of the pixel on the Desktop. If the color depth on your Desktop is less than 24-bit, all 24-bit colors will be displayed after approximating to the nearest supported color. ColorFinder will display the approximated color and NOT the actual color.