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XScrollBar - Scroll bar like Windows Media Player's

, 2 Sep 2008
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XScrollBar is a scroll bar that may be displayed with optional thumb color, thumb gripper, and channel color

Introduction

Recently I needed a scroll bar that looked and acted like the one in Windows Media Player:

screenshot

The closest one I could find was the CSkinHorizontalScrollbar class in Greg Ellis's article, but it did not support colors. So I created XScrollBar, which has following features:

  • Support for both horizontal and vertical scroll bars
  • Optional color displayed on thumb and in channel
  • Optional gripper displayed on thumb
  • Hand cursor is displayed when mouse hovers over thumb
  • Thumb color (if enabled) is changed to "hot color" when mouse hovers over thumb
  • Hot/pressed states displayed for arrow buttons
  • Thumb changes to hot state when control has focus
  • Responds to both mouse and keyboard input
  • Clicking in channel moves thumb to that spot (which is more intuitive than behavior of standard CScrollBar)
  • Left and right arrow buttons move thumb by one unit
  • Scroll messages (WM_HSCROLL) are sent to owner window
  • The scroll bar and its components should be sized according to the size of a specified rect

CXScrollBar In Action

To demonstrate new scroll bar, I decided to create an RGB color tool, which would benefit from having colors displayed on scroll bars:

screenshot

Turning off thumb color also turns off channel color:

screenshot

You can also turn off channel color by itself:

screenshot

The thumb gripper can also be disabled:

screenshot

Using CXScrollBar

Use of XScrollBar will usually be in dialogs, but you can create XScrollBar anywhere by using one of the two Create functions.

CreateFromWindow()

//=============================================================================
//
// CreateFromWindow
//
// Purpose:     Create the CXScrollBar control from placeholder window
//
// Parameters:  dwStyle    - the scroll bar’s style. Typically this will be
//                           SBS_HORZ|WS_CHILD|SS_LEFT|SS_NOTIFY|WS_VISIBLE.
//              pParentWnd - the scroll bar’s parent window, usually a CDialog
//                           object. It must not be NULL.
//              hWnd       - HWND of placeholder window (must already exist)
//              nId        - the resource id of the CXScrollBar control
//
// Returns:     BOOL       - TRUE = success
//

Here is how the CreateFromWindow() function is used in the demo app:

    // red
    VERIFY(m_HorizontalScrollBar1.CreateFromWindow(
        SBS_HORZ | WS_CHILD | WS_VISIBLE | WS_TABSTOP,
        this, GetDlgItem(IDC_SCROLL1_RECT_HORZ)->m_hWnd, IDC_SCROLL1_HORZ));

After creating the XScrollBar control, the demo app then sets its range, color, and gripper options:

    m_HorizontalScrollBar1.SetScrollRange(0, 255)
                          .SetThumbColor(RGB(255,0,0))
                          .EnableThumbGripper(m_bThumbGripper);

Setting thumb color also has effect of enabling display of thumb color. The channel color is enabled by default, and will be displayed if thumb color is enabled.

CreateFromRect()

In case it is not convenient to create a placeholder window, you can also create XScrollBar control by specifying rect:

//=============================================================================
//
// CreateFromRect
//
// Purpose:     Create the CXScrollBar control from rect
//
// Parameters:  dwStyle    - the scroll bar’s style. Typically this will be
//                           SBS_HORZ|WS_CHILD|SS_LEFT|SS_NOTIFY|WS_VISIBLE.
//              pParentWnd - the scroll bar’s parent window, usually a CDialog
//                           object. It must not be NULL.
//              rect       - the size and position of the window, in client 
//                           coordinates of pParentWnd
//              nId        - the resource id of the CXScrollBar control
//
// Returns:     BOOL       - TRUE = success
//

Implementation Notes

XScrollBar Component Structure

The diagram below shows the components of an XScollBar, and the nomenclature that will be used in this article:

screenshot

As you probably guessed, the XScrollBar is drawn in five steps (six, if you count the border). The drawing takes place in DrawHorizontal() function.

Drawing the XScrollBar: Step 1 - Left Arrow Button

The left arrow button bitmap looks like this (the orange border is not part of the bitmap):

screenshot

One thing to note is that arrow bitmaps and thumb bitmap are assumed to be all the same size, which simplifies some calculations. The size of the thumb bitmap (m_nBitmapWidth, m_nBitmapHeight) is set in the CreateFromStatic() function.

Knowing that width of the left arrow bitmap = width of the thumb bitmap, we can write

    CRect rectLeftArrow(m_rectClient.left, m_rectClient.top,
        m_rectClient.left + m_nBitmapWidth, m_rectClient.bottom);

StretchBlt() is then called to copy the left arrow bitmap into the memory DC, and a border is drawn around the left arrow. Note that the bitmaps do not include a border, because StretchBlt() may decide to duplicate the row that contains the border, and you will end up with a thick line on the bottom.

Drawing the XScrollBar: Steps 2 & 3 - Channel

Next we draw channel. In case a color is being displayed in the channel, it must be drawn in two parts. Because we modify the bitmap to add color, we draw the right channel (the part without color) first.

The channel bitmap is one pixel wide and looks like this (the orange border is not part of the bitmap):

screenshot

Earlier, we set the channel position and width from the thumb width:

    int nChannelStart = m_rectClient.left + m_nBitmapWidth;
    int nChannelWidth = m_rectClient.Width() - 2*m_nBitmapWidth;

Now we use these values to define the rect for the right channel:

    CRect rectChannelRight(m_rectThumb.left + m_nBitmapWidth/2, m_rectClient.top,
    nChannelStart + nChannelWidth, m_rectClient.bottom);

StretchBlt() is then called to copy the right channel bitmap into the memory DC.

If a thumb color and channel color (both are required) are desired, then we must modify the channel bitmap to add color. But what color to use? Here is where Christian Rodemeyer's CColor class comes in. We use CColor to convert the RGB thumb color to HLS, and then lighten the color by adjusting the HLS values. Finally, we convert back to RGB, and this is new channel color.

    if (m_bChannelColor && m_bThumbColor)
    {
        COLORREF rgb1, rgb2, rgb3;
        GetChannelColors(rgb1, rgb2, rgb3);

        BITMAP bm;
        bmpChannel.GetBitmap(&bm);

        // set highlight colors
        bitmapDC.SetPixel(0, 0, rgb1);
        bitmapDC.SetPixel(0, 1, rgb2);

        // set main color
        for (int y = 2; y < (bm.bmHeight); y++)
            bitmapDC.SetPixel(0, y, rgb3);
    }

and here is GetChannelColors():

//=============================================================================
void CXScrollBar::GetChannelColors(COLORREF& rgb1, 
                                   COLORREF& rgb2, 
                                   COLORREF& rgb3)
//=============================================================================
{
    CColor color;
    color.SetRGB(GetRValue(m_ThumbColor),
                 GetGValue(m_ThumbColor), 
                 GetBValue(m_ThumbColor));
    color.ToHLS();
    float fLuminance = color.GetLuminance();

    // use 80% L, 50% S for main color
    fLuminance = 0.8f;
    float fSaturation = color.GetSaturation();
    fSaturation = 0.5f * fSaturation;
    float fHue = color.GetHue();
    color.SetHLS(fHue, fLuminance, fSaturation);
    color.ToRGB();
    rgb3 = RGB(color.GetRed(), color.GetGreen(), color.GetBlue());

    // use .87 L for second highlight color
    fLuminance = .87f;
    color.SetHLS(fHue, fLuminance, fSaturation);
    color.ToRGB();
    rgb2 = RGB(color.GetRed(), color.GetGreen(), color.GetBlue());

    // use .92 L for first highlight color
    fLuminance = .92f;
    color.SetHLS(fHue, fLuminance, fSaturation);
    color.ToRGB();
    rgb1 = RGB(color.GetRed(), color.GetGreen(), color.GetBlue());
}

We can now define the rect for the left channel:

    CRect rectChannelLeft(nChannelStart, m_rectClient.top,
        m_rectThumb.left + m_nBitmapWidth/2, m_rectClient.bottom);

StretchBlt() is then called to copy the left channel bitmap into the memory DC

Drawing the XScrollBar: Step 4 - Right Arrow Button

The right arrow button bitmap looks like this (the orange border is not part of the bitmap):

screenshot

The right arrow button is drawn much like the left arrow button.

Drawing the XScrollBar: Step 5 - Thumb

The thumb bitmap (for a thumb with no color) looks like this:

screenshot

For a thumb with color it looks like:

screenshot

The thumb bitmaps are modified before being drawn to the memory DC. For a thumb with no color, the only modification that may be necessary is to replace the thumb gripper pixels with pixels taken from the surrounding area on the thumb, thus making the gripper disappear (how this is done will be explained below).

For a thumb with color, in addition to the gripper pixels, it is also necessary to make the corner pixels transparent (i.e., same color as channel). and to add the selected thumb color (or hover color). All these changes are accomplished by using four "special" RGB color values:

RGB Value Use
RGB(0, 0, 1) Thumb color (or hover color)
RGB(0, 0, 2) Gripper
RGB(0, 0, 3) Transparent left color
RGB(0, 0, 4) Transparent right color

These colors are used in the thumb bitmaps as shown here:

screenshot

Note that the thumb with no color only has the RGB(0, 0, 2) color.

Here is the code that performs these pixel replacements:

    CClientDC dc(this);

    CDC bitmapDC;
    bitmapDC.CreateCompatibleDC(&dc);

    CBitmap *pOldBitmap = bitmapDC.SelectObject(&m_bmpThumbHot);

    // add desired hot color to thumb
    ColorThumb(&bitmapDC, m_ThumbHoverColor);

    bitmapDC.SelectObject(&m_bmpThumb);

    // add desired cold color to thumb
    ColorThumb(&bitmapDC, m_ThumbColor);

and here is ColorThumb():

//=============================================================================
void CXScrollBar::ColorThumb(CDC *pDC, COLORREF rgbThumb)
//=============================================================================
{
    COLORREF rgbPrev = 0;

    // add desired hot color to thumb
    for (int x = 0; x < m_nBitmapWidth; x++)
    {
        for (int y = 0; y < m_nBitmapHeight; y++)
        {
            COLORREF rgb = pDC->GetPixel(x, y);

            if (m_bThumbColor && (rgb == THUMB_MASK_COLOR))
            {
                pDC->SetPixel(x, y, rgbThumb);
            }
            else if (rgb == THUMB_GRIPPER_MASK_COLOR)
            {
                if (m_bThumbGripper)
                    pDC->SetPixel(x, y, THUMB_GRIPPER_COLOR);
                else
                    pDC->SetPixel(x, y, rgbPrev);
            }

            rgbPrev = rgb;
        }
    }
}

This technique for coloring the thumb and channel works for True Color (24-bit). Lower resolutions may require you to use other RGB values for the four "special" RGB thumb colors, and it may also require that you limit the color used in the channel.

Mouse Hover

A final thing to take care of is when the mouse hovers over the thumb. In this case, the thumb color will be changed to the hover color (as seen in the above code), and the cursor will be changed to a hand:

screenshot

This is handled in the OnSetCursor() function.

How To Use

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

  • XScrollBar.cpp
  • XScrollBar.h
  • Color.cpp
  • Color.h
  • memdc.h

Next copy the bitmap files to the project's res directory, and add the bitmaps to the .rc file. I find it easiest just to edit the .rc file manually:

/////////////////////////////////////////////////////////////////////////////
//
// Bitmap
//
IDB_HORIZONTAL_SCROLLBAR_LEFTARROW BITMAP  DISCARDABLE      "res\\HorizontalScrollBarLeftArrow.bmp"
IDB_HORIZONTAL_SCROLLBAR_RIGHTARROW BITMAP  DISCARDABLE     "res\\HorizontalScrollBarRightArrow.bmp"
IDB_HORIZONTAL_SCROLLBAR_CHANNEL BITMAP  DISCARDABLE        "res\\HorizontalScrollBarChannel.bmp"
IDB_HORIZONTAL_SCROLLBAR_THUMB BITMAP  DISCARDABLE          "res\\HorizontalScrollBarThumb.bmp"
IDB_HORIZONTAL_SCROLLBAR_THUMB_NO_COLOR BITMAP  DISCARDABLE "res\\HorizontalScrollBarThumbNoColor.bmp"
IDB_VERTICAL_SCROLLBAR_UPARROW BITMAP  DISCARDABLE          "res\\VerticalScrollBarUpArrow.bmp"
IDB_VERTICAL_SCROLLBAR_DOWNARROW BITMAP  DISCARDABLE        "res\\VerticalScrollBarDownArrow.bmp"
IDB_VERTICAL_SCROLLBAR_CHANNEL BITMAP  DISCARDABLE          "res\\VerticalScrollBarChannel.bmp"
IDB_VERTICAL_SCROLLBAR_THUMB BITMAP  DISCARDABLE            "res\\VerticalScrollBarThumb.bmp"
IDB_VERTICAL_SCROLLBAR_THUMB_NO_COLOR BITMAP  DISCARDABLE   "res\\VerticalScrollBarThumbNoColor.bmp"
And add the bitmap IDs to resource.h:
#define IDB_HORIZONTAL_SCROLLBAR_LEFTARROW        201
#define IDB_HORIZONTAL_SCROLLBAR_RIGHTARROW       202
#define IDB_HORIZONTAL_SCROLLBAR_CHANNEL          203
#define IDB_HORIZONTAL_SCROLLBAR_THUMB            204
#define IDB_HORIZONTAL_SCROLLBAR_THUMB_NO_COLOR   205
#define IDB_VERTICAL_SCROLLBAR_UPARROW            206
#define IDB_VERTICAL_SCROLLBAR_DOWNARROW          207
#define IDB_VERTICAL_SCROLLBAR_CHANNEL            208
#define IDB_VERTICAL_SCROLLBAR_THUMB              209
#define IDB_VERTICAL_SCROLLBAR_THUMB_NO_COLOR     210

Of course, you should verify the numerical IDs are unique.

Future Enhancements

  • Add "scroll tip".
  • Add option to flip vertical orientation.

Acknowledgments

  • Thanks to Greg Ellis for his CSkinHorizontalScrollbar class, which I used as the starting point for CXScrollBar.
  • Thanks to Steve Mayfield for supplying the code for vertical scroll bars.
  • Thanks to Christian Rodemeyer for his CColor class.
  • I used HPS PixelColor to capture screen colors and inspect the scroll bar on the screen.
  • I used Impict, which ships with Help & Manual, to annotate the images.

Revision History

Version 1.2 - 2008 August 29

  • Optimized bitmap loading
  • Changed to CWnd
  • Added hot state to arrows and thumb (no color)
  • Added pressed state to arrows
  • Focus shown by hot state of thumb
  • Added CreateFromWindow() and CreateFromRect() functions
  • Removed CreateFromStatic()
  • Added GetScrollRange()
  • Added keyboard input

Version 1.1 - 2004 September 21

  • Update with Steve Mayfield's vertical scroll bar implementation.

Version 1.0 - 2004 September 9

  • 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)

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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

 
QuestionBig orange box? Pinmembersk8er_boy2872-Sep-08 22:11 
What's with the big orange box on the left of the demo dialogs? That orange color looks familiar. I wonder where I've seen it before...Confused | :confused:
AnswerRe: Big orange box? PinmvpHans Dietrich2-Sep-08 22:23 

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