How to get size of check and gap in check box?

Question

I have a check box that I want to accurately measure so I can position controls on a dialog correctly. I can easily measure the size of the text on the control - but I don't know the "official" way of calculating the size of the check box and the gap before (or after) the text.

Answer 1

Short answer:

Long Version

From MSDN Layout Specifications: Win32, we have the specifications of the dimensions of a checkbox.

It is 12 dialog units from the left edge of the control to the start of the text:

And a checkbox control is 10 dialog units tall:

Surfaces and Controls	Height (DLUs)	Width (DLUs)
Check box	10	As wide as possible (usually to the margins) to accommodate localization requirements.

First we calculate the size of a horizontal and a vertical dialog unit:

const dluCheckBoxInternalSpacing = 12; //12 horizontal dlus
const dluCheckboxHeight = 10; //10 vertical dlus

Size dialogUnits = GetAveCharSize(dc);

Integer checkboxSpacing = MulDiv(dluCheckboxSpacing, dialogUnits.Width,  4); 
Integer checkboxHeight = MulDiv(dluCheckboxHeight,   dialogUnits.Height, 8);

Using the handy helper function:

Size GetAveCharSize(HDC dc)
{
   /*
      How To Calculate Dialog Base Units with Non-System-Based Font
      http://support.microsoft.com/kb/125681
   */
   TEXTMETRIC tm;
   GetTextMetrics(dc, ref tm);

   String buffer = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";    

   Size result;
   GetTextExtentPoint32(dc, buffer, 52, out result);

   result.Width = (result.X/26 + 1) / 2; //div uses trunc rounding; we want arithmetic rounding
   result.Height = tm.tmHeight;

   return result;
}

Now that we know how many pixels (checkboxSpacing) to add, we calculate the label size as normal:

textRect = Rect(0,0,0,0);
DrawText(dc, Caption, -1, textRect, DT_CALCRECT or DT_LEFT or DT_SINGLELINE);

chkVerification.Width = checkboxSpacing+textRect.Right;
chkVerification.Height = checkboxHeight;

Bonus Reading

What's a dialog unit?

A dialog is a unit of measure based on the user's preferred font size. A dialog unit is defined such that the average character is 4 dialog units wide by 8 dialog units high:

This means that dialog units:

• change with selected font
• changed with selected DPI setting
• are not square

Note: Any code released into public domain. No attribution required.

Answer 2

I'd like to give my 2 cents on the matter since iv spent an entire day working on an accurate solution for this problem that takes DPI awareness and fonts into consideration.

First define the checkbox's size in units.

#define CHECKBOX_INTERNAL_SIZE 12

Then i defined a function for converting units to pixels. NOTE: MulDiv may work just as good.

double dpi_MulDiv(double nNumber, double nNumerator, double nDenominator)
{
    return (nNumber * nNumerator) / nDenominator;
}

Finally the function that does the magic. SEE the code comments for details.

//
// Get the minimum size of the Checkbox.
//   NOTE: The font of the control must be set before calling this function.
//
SIZE dpi_GetCheckBoxWidth(HWND hWnd, int monitorDpi)
{
    HDC dc;
    HFONT hFont;
    HFONT oldFont;
    TEXTMETRIC tm;
    double checkboxSize;
    double whiteSpace;
    WCHAR sourceString[128];
    RECT txtRect;
    SIZE size;

    dc = GetDC(hWnd);

    // Note that GetDC returns an uninitialized DC, which has "System" (a bitmap font) as the default font; thus the need to select a font into the DC.

    hFont = (HFONT)SendMessage(hWnd, WM_GETFONT, 0, 0);
    oldFont = (HFONT)SelectObject(dc, hFont);

    // Get the Checkbox width.

    checkboxSize = round(dpi_MulDiv(CHECKBOX_INTERNAL_SIZE, monitorDpi, 96));

    // Get the space between the Checkbox and text.

    GetTextMetrics(dc, &tm);
    whiteSpace = round((double)tm.tmAveCharWidth / 2.0f);

    // Get the Text width.

    txtRect = { 0, 0, 0, 0 };
    if (GetWindowTextW(hWnd, sourceString, 128) != 0)
    {
        DrawTextW(dc, sourceString, -1, &txtRect, DT_CALCRECT | DT_LEFT | DT_SINGLELINE);
    }

    // Cleanup.

    SelectObject(dc, oldFont);
    ReleaseDC(hWnd, dc);

    // Done.

    size.cx = (LONG)checkboxSize + (LONG)whiteSpace + txtRect.right + 3;
    size.cy = ((LONG)checkboxSize < txtRect.bottom) ? txtRect.bottom : (LONG)checkboxSize;

    return size;
}

I added + 3 on the last line that computes the width as a way to adjust for little irregularities. Feed back on this is welcomed. Iv only tested on Windows 10 thus far with different fonts and sizes.

Answer 3

Sorry for resurrecting this old thread. I recently found myself wondering about the exact same question. Currently, none of the answers above give a result consistent with Windows 10 for different fonts and font sizes, especially in high-DPI environments.

Instead, it seems that the correct result is obtained by

SIZE szCheckBox;
GetThemePartSize(hTheme, hDC, BP_CHECKBOX, CBS_UNCHECKEDNORMAL, &rcBackgroundContent, TS_TRUE, &szCheckBox);

for the size of the checkbox itself. And

SIZE szZeroCharacter;
GetTextExtentPoint32(hDC, L"0", 1, &szZeroCharacter);
int iGapWidth = szZeroCharacter.cx / 2;

for the width of the gap. After trying a lot of different methods inspired by the posts above, I found L"0" in the dissembly of comctl32.dll. And while it looks like a joke to me (not necessarily a good one), I suspect it's a holdover from the old days when this might have been a good enough approximation of 2DLU.

Disclaimer: While I tested the result with various fonts and different sizes on Windows 10, I have not attempted to verify that it also holds on any other (older) version of the operating system.

Answer 4

Preamble:
I had the same question while trying to determine the needed size of the checkbox control for a given text and found that the existing answers didn't really work for me, for several reasons:

• SM_CXMENUCHECK doesn't account for the gap. In fact, I'm not convinced this is even for regular checkboxes, although it may have the same value. It may also be dependent on visual styles being enabled.
• The other answers were overly complicated and felt a bit hacky (no disrespect intended, it is MS that don't make this easy).
• The stated 12DLU layout was very helpful, although again feels arbitrary without a system metric to rely on.
• The answers I tried still didn't yield a high enough pixel value to stop the checkbox text from wrapping.

My investigation:
I looked at how Wine reproduces the behavior and found that it also gives the same results as simply assuming 12DLU. However, the text still wrapped unless I added an extra 3 pixels to the width (even though the text should fit fine without). I also noticed that GetTextExtentPoint32 yields a value of 3 for an empty string (hmmm...)
Turning off the BS_MULTILINE style obviously stopped the text wrapping. My guess is that DrawTextW's word wrapping calculations are imperfect.
At this point I decided that the simplest solution was to just add 1 extra space to GetTextExtentPoint32, so that there would definitely be enough pixels. The over-estimate of a couple of pixels was acceptable to me.

Note that this all assumes your application is manifested as DPI aware. Otherwise I found the checkbox appeared much larger on some Windows 7 systems (not all though).

My (mostly Wine's) solution:

// This code gets the size of a piece of text and adds the size of a
// checkbox and gap. Note that this is very rough code with no error handling.
BOOL isCheckbox = TRUE;
HWND dialog = ... // Your control or dialog
HFONT font = ... // The font your control will use if it hasn't been set yet
PTCHAR text = ... // Your text
HFONT currentFont;
SIZE size;
HDC dc = GetDC(dialog);
if (!font) {
    font = (HFONT)SendMessage(dialog, WM_GETFONT, 0, 0);
}
currentFont = (HFONT)SelectObject(dc, font); // NB: You should add error handling here
if (isCheckbox) {
    // Or you can disable BS_MULTILINE
    _tcscat(text, TEXT(" ")); // NB: This assumes text is allocated for +1 char
}
GetTextExtentPoint32(dc, text, _tcslen(text), &size); // NB: You should add error handling here
if (isCheckbox) {
    int checkBoxWidth  = 12 * GetDeviceCaps(dc, LOGPIXELSX ) / 96 + 1;
    int checkBoxHeight = 12 * GetDeviceCaps(dc, LOGPIXELSY ) / 96 + 1;
    int textOffset;
    GetCharWidthW(dc, '0', '0', &textOffset);
    textOffset /= 2;
    size->cx += checkBoxWidth + textOffset;
    if (size->cy < checkBoxHeight) {
        size->cy = checkBoxHeight;
    }
}
if (currentFont) {
    SelectObject(dc, currentFont);
}
ReleaseDC(dialog, dc);

Answer 5

Ok dudes my way is maybe not the fastes to use in runtime, but it works for me in any case i have tested so far. In the beginnin of my proggys i put in a function to get the size and store it in a global variable (yeah i have heard this would be bad, but i dont care about this)

here the explanation:

1. Create a treeview (invisible if u want)
2. Create an imagelist with atleast 1 image inside (size 16x16)
3. Set the imagelist to the treeview ("TVSIL_NORMAL")
4. Get the "TVSIL_STATE" imagelist from the treeview (u have to create "TVSIL_NORMAL" before, otherwise this one will fail!)
5. Use ImageList_GetIconSize(..) and store the size. Wow, the checkboxs and the radio-buttons have the same size as the state icons of the treeview. Now u have what u want!
6. Destroy the "TVSIL_NORMAL" imagelist
7. Destroy the treeview

this code needs only a few microseconds at the beginning of my proggies and i can use the value everytime i need it.

Answer 6

It is a shame that Microsoft did not provide a way to know this for sure. I was struggling with the same question and the answer provided above is not complete. The main problem with it is that if the font of the dialog window is set to something other than the default size, that solution will not work because checkboxes will be resized.

Here's how I solved this issue (it is just an approximation that seems to have worked for me). The code is for MFC project.

1 - Create two test controls on your form, a checkbox and a radio box:

2 - Define the following custom struct:

struct CHECKBOX_DIMS{
    int nWidthPx;
    int nHeightPx;
    int nSpacePx;       //Space between checkbox and text

    CHECKBOX_DIMS()
    {
        nWidthPx = 0;
        nHeightPx = 0;
        nSpacePx = 0;
    }
};

3 - Call the following code when form initializes for each of the test controls (that will measure them and remove them so that end-users don't seem them):

BOOL OnInitDialog()
{
    CDialog::OnInitDialog();

    //Calculate the size of a checkbox & radio box
    VERIFY(GetInitialCheckBoxSize(IDC_CHECK_TEST, &dimsCheckBox, TRUE));
    VERIFY(GetInitialCheckBoxSize(IDC_RADIO_TEST, &dimsRadioBox, TRUE));

    //Continue with form initialization ...
}

BOOL GetInitialCheckBoxSize(UINT nCtrlID, CHECKBOX_DIMS* pOutCD, BOOL bRemoveCtrl)
{
    //Must be called initially to calculate the size of a checkbox/radiobox
    //'nCtrlID' = control ID to measure
    //'pOutCD' = if not NULL, receives the dimensitions
    //'bRemoveCtrl' = TRUE to delete control
    //RETURN:
    //      = TRUE if success
    BOOL bRes = FALSE;

    //Get size of a check (not exactly what we need)
    int nCheckW = GetSystemMetrics(SM_CXMENUCHECK);
    int nCheckH = GetSystemMetrics(SM_CYMENUCHECK);

    //3D border spacer (not exactly what we need either)
    int nSpacerW = GetSystemMetrics(SM_CXEDGE);

    //Get test checkbox
    CButton* pChkWnd = (CButton*)GetDlgItem(nCtrlID);
    ASSERT(pChkWnd);

    if(pChkWnd)
    {
        CRect rcCheckBx;
        pChkWnd->GetWindowRect(&rcCheckBx);

        //We need only the height
        //INFO: The reason why we can't use the width is because there's
        //      an arbitrary text followed by a spacer...
        int h = rcCheckBx.Height();

        CDC* pDc = pChkWnd->GetDC();
        if(pDc)
        {
            //Get horizontal DPI setting
            int dpiX = pDc->GetDeviceCaps(LOGPIXELSX);

            //Calculate
            if(pOutCD)
            {
                //Use height as-is
                pOutCD->nHeightPx = h;

                //Use height for the width
                pOutCD->nWidthPx = (int)(h * ((double)nCheckW / nCheckH));

                //Spacer is the hardest
                //INFO: Assume twice and a half the size of 3D border & 
                //      take into account DPI setting for the window
                //      (It will give some extra space, but it's better than less space.)
                //      (This number is purely experimental.)
                //      (96 is Windows DPI setting for 100% resolution setting.)
                pOutCD->nSpacePx = (int)(nSpacerW * 2.5 * dpiX / 96.0);
            }

            //Release DC
            pChkWnd->ReleaseDC(pDc);

            if(bRemoveCtrl)
            {
                //Delete window
                bRes = pChkWnd->DestroyWindow();
            }
            else
            {
                //Keep the window
                bRes = TRUE;
            }
        }
    }

    return bRes;
}

4 - Now you can easily resize any checkbox or radio box by calling this:

//Set checkbox size & new text
VERIFY(SetCheckBoxTextAndSize(this, IDC_CHECK_ID, &dimsCheckBox, L"New text") > 0);

//Just resize radio box
VERIFY(SetCheckBoxTextAndSize(this, IDC_RADIO_ID, &dimsRadioBox, NULL) > 0);

int SetCheckBoxTextAndSize(CWnd* pParWnd, UINT nCheckBoxID, CHECKBOX_DIMS* pDims, LPCTSTR pNewText)
{
    //Set size of the checkbox/radio to 'pNewText' and update its size according to its text
    //'pParWnd' = parent dialog window
    //'nCheckBoxID' = control ID to resize (checkbox or radio box)
    //'pDims' = pointer to the struct with checkbox/radiobox dimensions
    //'pNewText' = text to set, or NULL not to change the text
    //RETURN:
    //          = New width of the control in pixels, or
    //          = 0 if error
    int nRes = 0;
    ASSERT(pParWnd);
    ASSERT(pDims);

    CButton* pChkWnd = (CButton*)pParWnd->GetDlgItem(nCheckBoxID);
    ASSERT(pChkWnd);

    if(pChkWnd)
    {
        CDC* pDc = pChkWnd->GetDC();
        CFont* pFont = pChkWnd->GetFont();
        if(pDc)
        {
            if(pFont)
            {
                //Make logfont
                LOGFONT lf = {0};
                if(pFont->GetLogFont(&lf))
                {
                    //Make new font
                    CFont font;
                    if(font.CreateFontIndirect(&lf))
                    {
                        //Get font from control
                        CFont* pOldFont = pDc->SelectObject(&font);

                        //Get text to set
                        CString strCheck;

                        if(pNewText)
                        {
                            //Use new text
                            strCheck = pNewText;
                        }
                        else
                        {
                            //Keep old text
                            pChkWnd->GetWindowText(strCheck);
                        }

                        //Calculate size
                        RECT rc = {0, 0, 0, 0};
                        ::DrawText(pDc->GetSafeHdc(), strCheck, strCheck.GetLength(), &rc, DT_CALCRECT | DT_NOPREFIX | DT_SINGLELINE);

                        //Get text width
                        int nTextWidth = abs(rc.right - rc.left);

                        //See if it's valid
                        if(nTextWidth > 0 ||
                            (nTextWidth == 0 && strCheck.GetLength() == 0))
                        {
                            //Get location of checkbox
                            CRect rcChk;
                            pChkWnd->GetWindowRect(&rcChk);
                            pParWnd->ScreenToClient(rcChk);

                            //Update its size
                            rcChk.right = rcChk.left + pDims->nWidthPx + pDims->nSpacePx + nTextWidth;

                            //Use this line if you want to change the height as well
                            //rcChk.bottom = rcChk.top + pDims->nHeightPx;

                            //Move the control
                            pChkWnd->MoveWindow(rcChk);

                            //Setting new text?
                            if(pNewText)
                            {
                                pChkWnd->SetWindowText(pNewText);
                            }

                            //Done
                            nRes = abs(rcChk.right - rcChk.left);
                        }


                        //Set font back
                        pDc->SelectObject(pOldFont);
                    }
                }
            }

            //Release DC
            pChkWnd->ReleaseDC(pDc);
        }
    }

    return nRes;
}

Answer 7

This code doesn't work on Win7 with scaled UI (fonts 125% larger or 150% larger). The only thing that seems to work is:

int WID = 13 * dc.GetDeviceCaps(LOGPIXELSX) / 96; 
int HEI = 13 * dc.GetDeviceCaps(LOGPIXELSY) / 96;

Answer 8

I'm pretty sure the width of the checkbox is equal to

int x = GetSystemMetrics( SM_CXMENUCHECK );
int y = GetSystemMetrics( SM_CYMENUCHECK );

You can then work out the area inside by subtracting the following ...

   int xInner = GetSystemMetrics( SM_CXEDGE );
   int yInner = GetSystemMetrics( SM_CYEDGE );

I use that in my code and haven't had a problem thus far ...