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XColorSpectrumCtrl - a non-MFC color picker control that displays a color spectrum

, 4 Apr 2008
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XColorSpectrumCtrl displays a color spectrum that allows user selection, and provides APIs for color based on RGB and HSL color models.

Introduction

XColorSpectrumCtrl mimics behavior of spectrum control on custom page of Microsoft Office® color picker:

screenshot

This is companion article to my XColorHexagonCtrl article, but you need not read that article to make use of this control.

XColorSpectrumCtrl Features and Behaviors

The XColorSpectrumCtrl control has two areas of user interaction, the spectrum and the slider:

screenshot

Each of the areas has its own selection indicator, the crosshair and the arrow.

These user interface behaviors are implemented in XColorSpectrumCtrl:

screenshot Clicking on spectrum or slider sends WM_XCOLORPICKER_SELCHANGE message to parent window, with RGB (COLORREF) color as WPARAM and control id as LPARAM.
screenshot Double-clicking on spectrum or slider sends WM_XCOLORPICKER_SELENDOK message to parent window, with RGB (COLORREF) color as WPARAM and control id as LPARAM.
screenshot When the control has focus, focus will be shown separately for spectrum vs. slider. Focus on spectrum is indicated by black crosshair; lack of focus by white crosshair. Focus on slider is indicated by solid black arrow; lack of focus by arrow outlined in black, with gray interior. The TAB key (or SHIFT+TAB) may be used to step between spectrum and slider.
screenshot The arrow, Page Up, Page Down, Home and End keys may be used when either area of control has focus. They work identically in two areas, except that Home and End keys in the spectrum will move cursor to left or right edges, instead of top or bottom edges as in slider.
screenshot The selection indicators (crosshair and arrow) may be clicked and dragged to new position. This will result in multiple WM_XCOLORPICKER_SELCHANGE messages sent to parent window.
screenshot Tooltips in four formats may be optionally displayed for spectrum and luminosity slider.

The programmatic interface to XColorSpectrumCtrl attributes is very simple: just eight functions to get/set RGB and HSL values, background color, and tooltip format:

Function Description
COLORREF GetBackground() Retrieves current background color
void GetHSL(BYTE* h, BYTE* s, BYTE* l) Retrieves HSL values for current color
COLORREF GetRGB() Retrieves RGB value for current color
void GetTooltipFormat() Retrieves tooltip format
CXColorSpectrumCtrl& SetBackground(COLORREF cr) Sets background color
CXColorSpectrumCtrl& SetHSL(BYTE h, BYTE s, BYTE l) Sets color from HSL values
CXColorSpectrumCtrl& SetRGB(COLORREF cr) Sets color from RGB value
CXColorSpectrumCtrl& SetTooltipFormat(TOOLTIP_FORMAT eFormat) Sets tooltip format

Tooltip Formats

There are five options for XColorSpectrumCtrl tooltip format (including no tooltip). The tooltip will be shown both on spectrum and on luminosity slider:

RGB
screenshot
HTML
screenshot
VB
screenshot
HSL
screenshot

XColorSpectrumCtrl Color Models

XColorSpectrumCtrl allows you to work with either RGB or HSL color model, depending on requirements of your application.

The following information was extracted from online sources such as MSDN and Wikipedia [1, 2].

RGB Color Model

The RGB model is used to designate colors for displays and other devices that emit light. Valid red, green, and blue values range from 0 through 255, with 0 indicating minimum intensity and 255 indicating maximum intensity. The following illustration shows how primary colors red, green, and blue can be combined to produce four additional colors. (For display devices, the color black results when red, green, and blue values are set to 0. In display technology, black is absence of all colors.) [Source: MSDN]

screenshot

The RGB color model is the most widely used in web design. Typically, HTML authors refer to named colors or to so-called 216 web-safe colors.

In developing this control I have followed Microsoft convention (which seems to be arbitrary) of only allowing HSL values between 0 and 240. In some references and conversion algorithms you will find HSL values between 0 and 255. Some HSL representations even use degrees and percentages, as I discuss later.

The name HSL is often used interchangeably with HSI (I = Intensity) and HSB (B = Brightness); HSB is the name used in .Net.

HSL Color Model

HSL (Hue, Saturation, Luminosity) is alternative way of specifying color values. There is simple algorithm to convert between RGB color and HSL color. You don't get more colors with one or the other, but with HSL you get better control over color's appearance, in terms of color lightness/darkness (luminosity) and color intensity (saturation). For this reason, HSL is more intuitive way of dealing with color in some applications

The HSL color model is sometimes represented by wheel:

screenshot

This is representation used in proposed CSS3 Color Module recommendation, where hue is represented as angle of the color wheel. So red = 0 degrees, green = 120 degrees, etc. Saturation and luminosity are represented as percentages: 100% is full saturation, 0% luminosity is black, and 100% luminosity is white. To quote CSS3: The advantage of HSL over RGB is that it is far more intuitive: you can guess at the colors you want, and then tweak.

screenshot

To give an example of how to "tweak" using HSL, consider two named colors LawnGreen and Chartreuse:

Color Name HTML Hex HSL Color
LawnGreen #7CFC00 90°,100%,99%
Chartreuse #7FFF00 90°,100%,100%

HSL representation makes it obvious how close the two colors are. Of course, web designers have known about this for long time, and there are many color utilities that display both HTML hex and HSL values, such as HPS PixelColor.

CSS3 has not yet been formally approved; you can check status of various CSS3 modules here.

Getting back to XColorSpectrumCtrl, here are some colors and their HSL and RGB values as returned by XColorSpectrumCtrl control:

Color Name RGB HSL Color
Red 255,0,0 0,240,120
Maroon 128,0,0 0,240,60
Yellow 255,255,0 40,240,120
Lime 0,255,0 80,240,120
Green 0,128,0 80,240,60
Aqua 0,255,255 120,240,120
Blue 0,0,255 160,240,120
Navy 0,0,128 160,240,60
Magenta 255,0,255 200,240,120
Purple 128,0,128 200,240,60
White 255,255,255 0,0,240
Gray 128,128,128 0,0,120
Black 0,0,0 0,0,0
You can find more information about named colors here and here.

Implementation Notes

Initially I created XColorSpectrumCtrl using MFC. This is very fast way to construct and develop new user interface components, with many support classes in framework. Later, I decided that I might want to use XColorSpectrumCtrl with other languages besides C++, so I began process of conversion. I immediately discovered that two MFC classes I use very often - CDC and CRect - were so useful that I could not do without them. After looking at functions I use in both of these classes, I came up with minimalist replacement classes, CXDC and CXRect. These do not contain all functions of original classes, but have all functions I used in making XColorSpectrumCtrl, and can easily be expanded in future if necessary. The entire implementations of these new classes are contained in files CXCD.h and CXRect.h.

I also had to decide whether to bundle tooltip functionality with XColorSpectrumCtrl. Ultimately I liked the benefits that tooltips provided, so I created CXToolTipCtrl class in CXToolTipCtrl.h to replace standard MFC CToolTipCtrl.

Internal Design

One of the first problems I identified in the design is drawing speed. I knew that drawing spectrum would be very time consuming, compared to other parts of the control. To address this issue, I used old Win32 trick of caching DC. The first time the spectrum needs to be drawn, I create a persistent DC and bitmap. For subsequent drawing, I BitBlt the saved DC to target DC, and then do any additional drawing on that. Once I did this, the spectrum drew instantly with no discernible flicker at all.

I wasn't sure whether I would have to do the same trick when drawing luminosity slider (especially because I had made dumb coding error, which increased flicker, rather than reducing it). After a few bug fixes, drawing luminosity slider was just as rock-solid as drawing spectrum, with no flicker even in debug mode, and without having to resort to a persistent DC. This was definitely a plus, because the slider - unlike the spectrum - changes frequently; every time the user clicks on spectrum, or uses any nav key, the slider is redrawn using new hue and saturation (the slider arrow changes position only when user clicks on slider or uses nav keys in slider, to change luminosity).

Next came the crosshair and arrow indicators. I briefly considered hand-coding the drawing function using MoveTo(), LineTo(), etc., but quickly got sick of writing all that boring code, especially after I realized that the indicators would change appearance depending on whether their area of the control had internal focus:

With Focus
screenshot
Without Focus
screenshot
With Focus
screenshot
Without Focus
screenshot

I switched to using internal bit array; each pixel is represented by one BYTE, whose value determines whether the pixel should be drawn (if non-zero), and if so what color should be used. Here is bit array for slider arrow:

    // For each byte in this array:
    //     0 = skip
    //     1 = COLOR_WINDOWTEXT
    //     2 = COLOR_WINDOWTEXT (COLOR_BTNSHADOW if bHasFocus == FALSE)
    static BYTE pixels[ARROW_HEIGHT][ARROW_WIDTH] = 
    {
        0,0,0,0,0,0,0,0,1,0,   // 1
        0,0,0,0,0,0,0,1,1,0,   // 2
        0,0,0,0,0,0,1,2,1,0,   // 3
        0,0,0,0,0,1,2,2,1,0,   // 4
        0,0,0,0,1,2,2,2,1,0,   // 5
        0,0,0,1,2,2,2,2,1,0,   // 6
        0,0,1,2,2,2,2,2,1,0,   // 7
        0,1,2,2,2,2,2,2,1,0,   // 8
        1,2,2,2,2,2,2,2,1,0,   // 9
        0,1,2,2,2,2,2,2,1,0,   // 10
        0,0,1,2,2,2,2,2,1,0,   // 11
        0,0,0,1,2,2,2,2,1,0,   // 12
        0,0,0,0,1,2,2,2,1,0,   // 13
        0,0,0,0,0,1,2,2,1,0,   // 14
        0,0,0,0,0,0,1,2,1,0,   // 15
        0,0,0,0,0,0,0,1,1,0,   // 16
        0,0,0,0,0,0,0,0,1,0    // 17
    };

In each pixel location where '2' appears, the color will depend on state of internal focus.

The only other major issue I had to contend with is tab key. In the MS Office® color picker Standard page, you can see that tabbing through all the controls on that property page will jump from spectrum to slider in forward direction, and from slider to spectrum in reverse (SHIFT+TAB) direction. However, XColorSpectrumCtrl is one control, not two, and so it must catch and handle the tab key internally. This involved two things: first, XColorSpectrumCtrl returns the code DLGC_WANTARROWS | DLGC_WANTTAB when it receives WM_GETDLGCODE message. This tells system that XColorSpectrumCtrl wants to receive arrow keys and tab keys, when it has the focus.

The second thing was to keep track of whether the spectrum or the slider had (internal) focus, to know how to respond to tab key presses. When user is tabbing out of control, XColorSpectrumCtrl sends WM_NEXTDLGCTL to parent dialog window, allowing it to decide what control to give the focus to.

The visual rendering of the control consisted mostly of getting the sizes and spacing correct. I could tell from MS Office® color picker how big things needed to be, but other things were not so obvious. For example, the control had to allow some vertical room for the slider arrow, which could extend above and below the spectrum drawing area:

screenshot
Yellow background for clarity.

Demo App

Here is what demo app looks like:

screenshot

Note that axis marks and labels are not part of control.

How to use

The following steps assume you want to add XColorSpectrumCtrl to a dialog. Steps would be similar for CFormView or CPropertyPage.

Step 1 - Add Files

To integrate CXColorSpectrumCtrl into your app, you first need to add following files to your project:

  • CXCD.h
  • CXRect.h
  • CXToolTipCtrl.h
  • XColorSpectrumCtrl.cpp
  • XColorSpectrumCtrl.h
  • rgbhsl.cpp
  • rgbhsl.h

The .cpp files should be set to Not using precompiled header in Visual Studio. Otherwise, you will get error

    fatal error C1010: unexpected end of file while looking for precompiled header directive

Step 2 - Add Placeholder Rect to Dialog Resource

Next add a STATIC or other control to dialog resource, where you want the XColorSpectrumCtrl to be displayed. The dialog for demo app looks like this:

screenshot

Note that this step is not required, if you have some other way to specify where XColorSpectrumCtrl should be displayed.

Step 3 - Create the Control

You need to do two things here: first, add #include statement to dialog class header file:
#include <span class="code-string">"XColorSpectrumCtrl.h"</span>
and insert variable that looks like:
    CXColorSpectrumCtrl m_ColorSpectrum;
Second, add code to OnInitDialog() function:
    CRect rect;
    GetDlgItem(IDC_FRAME)->GetWindowRect(&rect);
    ScreenToClient(&rect);
    GetDlgItem(IDC_FRAME)->ShowWindow(SW_HIDE);         // hide placeholder
    VERIFY(m_ColorSpectrum.Create(AfxGetInstanceHandle(), 
        WS_CHILD | WS_VISIBLE | WS_TABSTOP,             // styles 
        rect,                                           // control rect
        m_hWnd,                                         // parent window
        9001,                                           // control id
        RGB(0,255,0)),                                  // initial color
        CXColorSpectrumCtrl::XCOLOR_TOOLTIP_HTML));     // tooltip format

    // call SetWindowPos to insert control in proper place in tab order
    ::SetWindowPos(m_ColorSpectrum.m_hWnd, ::GetDlgItem(m_hWnd, IDC_FRAME), 
        0,0,0,0, SWP_NOMOVE|SWP_NOSIZE);

Step 4 - Add Message Handlers

According to your app's requirements, you may need to add handlers for one or both of the XColorSpectrumCtrl registered messages. Here are handlers used in demo app:
// handler for WM_XCOLORPICKER_SELCHANGE
LRESULT CXColorSpectrumCtrlTestDlg::OnSelChange(WPARAM wParam, LPARAM lParam)
{
    CString s = _T("");
    GetDlgItem(IDC_COLOR_NAME)->SetWindowText(s);
    GetDlgItem(IDC_COLOR_RGB)->SetWindowText(s);
    s.Format(_T("WM_XCOLORPICKER_SELCHANGE       RGB(%d,%d,%d)"), 
        GetRValue(wParam), GetGValue(wParam), GetBValue(wParam));
    if (lParam == 9001)
        GetDlgItem(IDC_SELECTION)->SetWindowText(s);
    return 0;
}

// handler for WM_XCOLORPICKER_SELENDOK
LRESULT CXColorSpectrumCtrlTestDlg::OnSelendOk(WPARAM wParam, LPARAM lParam)
{
    CString s = _T("");
    GetDlgItem(IDC_COLOR_NAME)->SetWindowText(s);
    GetDlgItem(IDC_COLOR_RGB)->SetWindowText(s);
    s.Format(_T("WM_XCOLORPICKER_SELENDOK       RGB(%d,%d,%d)"), 
        GetRValue(wParam), GetGValue(wParam), GetBValue(wParam));
    if (lParam == 9001)
        GetDlgItem(IDC_SELECTION)->SetWindowText(s);
    return 0;
}

Both messages send RGB color as wParam, and control id as lParam.

If you use XColorHexagonCtrl and XColorSpectrumCtrl together in the same project, you will notice that the extern variable names of the registered messages are different for the two controls. However, the actual message strings that are registered are the same, and so you can use the same handlers to handle both controls. You can tell which is which by using the control id returned in lParam.

Revision History

Version 1.1 - 2008 April 4

  • Bug fixes

Version 1.0 - 2008 March 12

  • Initial public release

Usage

This software is released into the public domain. You are free to use it in any way you like, except that you may not sell this source code. If you modify it or extend it, please to consider posting new code here for everyone to share. This software is provided "as is" with no expressed or implied warranty. I accept no liability for any damage or loss of business that this software may cause.

License

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

About the Author

Hans Dietrich
Software Developer (Senior) Hans Dietrich Software
United States United States
I attended St. Michael's College of the University of Toronto, with the intention of becoming a priest. A friend in the University's Computer Science Department got me interested in programming, and I have been hooked ever since.
 
Recently, I have moved to Los Angeles where I am doing consulting and development work.
 
For consulting and custom software development, please see www.hdsoft.org.






Comments and Discussions

 
GeneralError in VS6 PinmemberHaakon S.18-Jan-10 21:42 
GeneralCode questions... PinmemberRichard Perrine6-Jan-09 8:54 
I am getting deeper into c++ and would like to ask a couple of questions about this code:
 
1. it is non-MFC, but I seem to be having issues building/compiling it in VC++ 2005 Express. Any tips?
 
fatal error C1083: Cannot open include file: 'afxwin.h': No such file or directory
 
2. How would you make this picker be able select color on any part of the screen?
 

Thanks.
GeneralCleartype in screen shots not so clear... Pinmemberdgendreau7-Apr-08 6:45 
GeneralRe: Cleartype in screen shots not so clear... PinmvpHans Dietrich7-Apr-08 13:21 
GeneralGreat PinmemberSaurabh.Garg5-Apr-08 6:49 
GeneralRe: Great PinmvpHans Dietrich5-Apr-08 15:09 
GeneralVery Nice PinmvpJeffrey Walton24-Mar-08 6:20 
GeneralRe: Very Nice PinmvpHans Dietrich24-Mar-08 15:09 
GeneralExcellent PinmemberModulrob13-Mar-08 4:24 
GeneralExcellent Pinmemberx-b19-Mar-08 2:00 
GeneralGreat article and control PinmemberFranc Morales13-Mar-08 2:47 

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