SysWin Window Size and Position

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Window size and position

Reads and sets a window's position and size in pixels, and centres windows and controls.

Every function here takes a window handle: a top-level window, a dialog or a control. Sizes are in physical pixels unless the name ends in ForDpi, in which case the values you pass are 96-DPI units and are multiplied by the desktop's scaling ratio first, so 400 becomes 600 on a display set to 150 %.

Three rectangles describe a window:

Rectangle	Covers	Coordinates	Read it with
Window	the whole window: caption, borders, menu and, for a shown top-level window, the invisible resize border and drop shadow	screen	GetWindowRect
Bounds	the visible frame only, without the drop shadow	screen	GetWindowBounds
Client	the area inside the borders that the window paints itself	client: the top-left corner is always (0, 0)	GetWindowClientRect

The location of a child window or control is relative to its parent's client area; the location of a top-level window is relative to the screen.

Importing

#import "sys/win"
using win

Example

A window whose client area is 400 × 220 at 96 DPI on any display, centred in the work area, with a button that reports the three sizes in the caption:

#import "sys/win"
#import "sys/win/gui"
using win, gui

declare function WndProc( byval hwnd as HWND, byval uMsg as UINT, byval wParam as WPARAM, byval lParam as LPARAM ) as LRESULT

function main() as long
    SetProcessDpiAwareness( PROCESS_SYSTEM_DPI_AWARE )
    dim pWindow as CWindow = "SizeDemo"
    dim hWin as HWND = pWindow.Create( NULL, "Window size and position", @WndProc )
    SetWindowClientSizeForDpi( hWin, 400, 220 )
    CenterWindow( hWin )
    dim hButton as HWND = pWindow.AddControl( "Button", hWin, 100, "&Measure", 150, 90, 100, 30 )
    CenterControlH( hButton )
    return pWindow.DoEvents( SW_NORMAL )
end function

function WndProc( byval hwnd as HWND, byval uMsg as UINT, byval wParam as WPARAM, byval lParam as LPARAM ) as LRESULT
    select case uMsg
        case WM_COMMAND
            if CBCTL( wParam, lParam ) = 100 andalso CBCTLMSG( wParam, lParam ) = BN_CLICKED then
                var (l, t, r, b) = GetWindowBounds( hwnd )
                SetWindowText( hwnd, "window " & GetWindowWidth( hwnd ) & " x " & GetWindowHeight( hwnd ) & _
                                     ", frame " & ( r - l ) & " x " & ( b - t ) & _
                                     ", client " & GetWindowClientWidth( hwnd ) & " x " & GetWindowClientHeight( hwnd ) )
            end if
            return 0
        case WM_DESTROY
            PostQuitMessage( 0 )
            return 0
    end select
    return DefWindowProcW( hwnd, uMsg, wParam, lParam )
end function

end main()

On a typical Windows 11 display the window rectangle is 14 pixels wider than the visible frame: the difference is the invisible resize border.

Functions

Function	Does
GetWindowRect	Returns the window rectangle in screen coordinates.
GetWindowBounds	Returns the visible frame of a window, without its drop shadow.
GetWindowWidth	Returns the width of the window rectangle.
GetWindowHeight	Returns the height of the window rectangle.
GetWindowSize	Reads the width and height of the window rectangle into two variables.
SetWindowSize	Resizes a window without moving it.
SetWindowSizeForDpi	Resizes a window to a size given in 96-DPI units.
GetWindowClientRect	Returns the client rectangle.
GetWindowClientWidth	Returns the width of the client area.
GetWindowClientHeight	Returns the height of the client area.
SetWindowClientSize	Resizes a window so that its client area has a given size.
SetWindowClientSizeForDpi	Resizes a window so that its client area has a size given in 96-DPI units.
GetWindowLocation	Reads the top-left corner of a window, relative to its parent.
SetWindowLocation	Moves a window without resizing it.
SetWindowLocationForDpi	Moves a window to a position given in 96-DPI units.
SetWindowPosForDPI	Moves, resizes and reorders a window, with position and size in 96-DPI units.
MoveWindowForDPI	Moves and resizes a window, with position and size in 96-DPI units.
CenterWindow	Centres a window over its parent or in the work area.
CenterControlH	Centres a control horizontally in its parent.
CenterControlV	Centres a control vertically in its parent.
ForceVisibleDisplay	Moves a window that is off every screen back onto the nearest one.

Reference

GetWindowRect

function GetWindowRect( byval hWin as HWND ) as ( long, long, long, long )

Returns the window rectangle as ( left, top, right, bottom ), in screen coordinates. right and bottom are one past the last pixel, so right - left is the width.

The rectangle includes the caption, borders and menu. Once a top-level window has been shown it also includes the invisible resize border and the drop shadow; use GetWindowBounds for the frame the user sees. For the whole desktop pass GetDesktopWindow().

Parameter	Meaning
hWin	The window or control.

Returns the four edges. GetLastError() is nonzero afterwards when the call succeeded and 0 when it failed (an invalid handle gives four zeros).

The one-argument form belongs to win; the Windows function of the same name, which fills a RECT, is still there with two arguments.

Example

var (l, t, r, b) = GetWindowRect( hwnd )
if GetLastError() then print "left"; l; " top"; t; " width"; r - l; " height"; b - t

Microsoft Learn: GetWindowRect

GetWindowBounds

function GetWindowBounds( byval hWin as HWND ) as ( long, long, long, long )

Returns the visible frame of a window as ( left, top, right, bottom ), in screen coordinates: the window rectangle without the invisible resize border and the drop shadow. The values are physical pixels, not adjusted for DPI virtualisation.

The frame is only known once the window has been shown; before that the call fails.

Parameter	Meaning
hWin	A top-level window.

Returns the four edges. GetLastError() is S_OK (0) afterwards when the call succeeded, otherwise the failing HRESULT.

Example

var (l, t, r, b) = GetWindowBounds( hwnd )
if GetLastError() = S_OK then print "visible frame:"; r - l; " x"; b - t

Microsoft Learn: DwmGetWindowAttribute with DWMWA_EXTENDED_FRAME_BOUNDS

GetWindowWidth

function GetWindowWidth( byval hWin as HWND ) as long

Returns the width of the window rectangle in pixels, borders included. Pass GetDesktopWindow() for the width of the primary screen.

Returns the width, or 0 for an invalid handle.

Example

print "desktop width:"; GetWindowWidth( GetDesktopWindow() )

GetWindowHeight

function GetWindowHeight( byval hWin as HWND ) as long

Returns the height of the window rectangle in pixels, caption and borders included. Pass GetDesktopWindow() for the height of the primary screen.

Returns the height, or 0 for an invalid handle.

Example

print "window height:"; GetWindowHeight( hwnd )

GetWindowSize

function GetWindowSize( byval hWin as HWND, byref nWidth as long, byref nHeight as long ) as boolean

Reads the width and height of the window rectangle into nWidth and nHeight, in one call.

Parameter	Meaning
hWin	The window or control.
nWidth	Receives the width in pixels.
nHeight	Receives the height in pixels.

Returns true on success; on failure false, and GetLastError() says why.

Example

dim as long w, h
if GetWindowSize( hwnd, w, h ) then print w; " x"; h

SetWindowSize

function SetWindowSize( byval hWin as HWND, byval nWidth as long, byval nHeight as long ) as boolean

Resizes a window to nWidth × nHeight pixels, borders included. Its position and its place in the Z order stay as they are.

Returns true on success; on failure false, and GetLastError() says why.

Example

SetWindowSize( hwnd, 640, 480 )

Microsoft Learn: SetWindowPos

SetWindowSizeForDpi

function SetWindowSizeForDpi( byval hWin as HWND, byval nWidth as long, byval nHeight as long ) as boolean

Resizes a window like SetWindowSize, but nWidth and nHeight are 96-DPI units: each is multiplied by the desktop's scaling ratio (GetLogPixelsX() / 96 and GetLogPixelsY() / 96) first.

Returns true on success; on failure false, and GetLastError() says why.

Example

SetWindowSizeForDpi( hwnd, 640, 480 )   ' 960 x 720 at 150 %

GetWindowClientRect

function GetWindowClientRect( byval hWin as HWND ) as ( long, long, long, long )

Returns the client rectangle as ( left, top, right, bottom ). Client coordinates start at the top-left corner of the client area, so left and top are always 0 and right and bottom are the width and height.

Returns the four edges. GetLastError() is nonzero afterwards when the call succeeded and 0 when it failed.

Example

var (l, t, r, b) = GetWindowClientRect( hwnd )
if GetLastError() then print "client area:"; r; " x"; b

Microsoft Learn: GetClientRect

GetWindowClientWidth

function GetWindowClientWidth( byval hWin as HWND ) as long

Returns the width of the client area in pixels: the window's width less its borders and, if it has one, its vertical scroll bar.

Returns the width, or 0 for an invalid handle.

Example

print "client width:"; GetWindowClientWidth( hwnd )

GetWindowClientHeight

function GetWindowClientHeight( byval hWin as HWND ) as long

Returns the height of the client area in pixels: the window's height less its caption, menu, borders and, if it has one, its horizontal scroll bar.

Returns the height, or 0 for an invalid handle.

Example

print "client height:"; GetWindowClientHeight( hwnd )

SetWindowClientSize

sub SetWindowClientSize( byval hWin as HWND, byval nWidth as long, byval nHeight as long, byval rxRatio as single = 1, byval ryRatio as single = 1 )

Resizes a window so that its client area is nWidth × nHeight pixels, working out the borders, caption and menu from the window's own styles. A menu bar that wraps onto a second line and a horizontal or vertical scroll bar are allowed for. The window does not move or activate.

Parameter	Meaning
hWin	A window.
nWidth, nHeight	The client size wanted.
rxRatio, ryRatio	Optional factors each size is multiplied by first; 1 leaves it as given.

Example

SetWindowClientSize( hwnd, 400, 300 )

Microsoft Learn: AdjustWindowRectEx

SetWindowClientSizeForDpi

sub SetWindowClientSizeForDpi( byval hWin as HWND, byval nWidth as long, byval nHeight as long )

Resizes a window so that its client area is nWidth × nHeight 96-DPI units: the same as SetWindowClientSize with the desktop's horizontal and vertical scaling ratios passed as rxRatio and ryRatio. Use it to lay out a window once, at 96 DPI, and have it come out the same physical size on every display.

Example

SetWindowClientSizeForDpi( hwnd, 400, 300 )   ' 600 x 450 pixels at 150 %

GetWindowLocation

sub GetWindowLocation( byval hWin as HWND, byref nLeft as long, byref nTop as long )

Reads the top-left corner of a window, in pixels. For a control or child window the point is relative to the parent's client area; for a top-level window it is in screen coordinates.

Parameter	Meaning
hWin	The window or control.
nLeft	Receives the x coordinate.
nTop	Receives the y coordinate.

Example

dim as long x, y
GetWindowLocation( hCtrl, x, y )
print "the control is at"; x; ","; y

Microsoft Learn: MapWindowPoints

SetWindowLocation

function SetWindowLocation( byval hWin as HWND, byval nLeft as long, byval nTop as long ) as boolean

Moves a window so that its top-left corner is at (nLeft, nTop), in the same coordinates as GetWindowLocation. Its size and place in the Z order stay as they are.

Returns true on success; on failure false, and GetLastError() says why.

Example

SetWindowLocation( hCtrl, 10, 10 )

SetWindowLocationForDpi

function SetWindowLocationForDpi( byval hWin as HWND, byval nLeft as long, byval nTop as long ) as boolean

Moves a window like SetWindowLocation, but nLeft and nTop are 96-DPI units and are scaled by the desktop's ratios first.

Returns true on success; on failure false, and GetLastError() says why.

Example

SetWindowLocationForDpi( hCtrl, 10, 40 )   ' 15, 60 at 150 %

SetWindowPosForDPI

function SetWindowPosForDPI( byval hwnd as HWND, byval hWndInsertAfter as HWND, byval x as long, byval y as long, byval cx as long, byval cy as long, byval uFlags as UINT = SWP_NOZORDER ) as boolean

Calls Windows' SetWindowPos with x, y, cx and cy multiplied by the desktop's scaling ratios first, so they are given in 96-DPI units.

Parameter	Meaning
hwnd	The window.
hWndInsertAfter	The window to place it after in the Z order, or HWND_TOP, HWND_BOTTOM, HWND_TOPMOST, HWND_NOTOPMOST. Ignored with SWP_NOZORDER.
x, y	The new position.
cx, cy	The new size.
uFlags	SWP_* flags; the default keeps the Z order. Add SWP_NOMOVE or SWP_NOSIZE to keep the position or the size.

Returns true on success; on failure false, and GetLastError() says why.

Example

SetWindowPosForDPI( hCtrl, NULL, 20, 20, 120, 28 )

Microsoft Learn: SetWindowPos

MoveWindowForDPI

function MoveWindowForDPI( byval hwnd as HWND, byval x as long, byval y as long, byval nWidth as long, byval nHeight as long, byval bRepaint as boolean = true ) as boolean

Calls Windows' MoveWindow with the position and size multiplied by the desktop's scaling ratios first, so they are given in 96-DPI units.

Parameter	Meaning
hwnd	The window.
x, y	The new position.
nWidth, nHeight	The new size.
bRepaint	true (the default) repaints the window after the move.

Returns true on success; on failure false, and GetLastError() says why.

Example

MoveWindowForDPI( hCtrl, 20, 60, 200, 24 )

Microsoft Learn: MoveWindow

CenterWindow

sub CenterWindow( byval hWin as HWND = NULL, byval hwndParent as HWND = NULL )

Centres a window over hwndParent, or in the work area of the primary display when hwndParent is NULL. The result is kept inside the work area (the screen less the taskbar), so a window centred over a parent near the edge stops at the edge. The size and Z order do not change.

To centre a child window, pass its parent as hwndParent.

Parameter	Meaning
hWin	The window to move.
hwndParent	The window to centre over, or NULL for the work area.

Example

CenterWindow( hwnd )                    ' in the work area
CenterWindow( hDlg, hwnd )              ' over its owner

Microsoft Learn: SystemParametersInfoW with SPI_GETWORKAREA

CenterControlH

sub CenterControlH( byval hCtrl as HWND )

Moves a control so that it is centred horizontally in its parent's client area. Its vertical position and its size stay as they are.

Example

CenterControlH( hCtrl )

CenterControlV

sub CenterControlV( byval hCtrl as HWND )

Moves a control so that it is centred vertically in its parent's client area.

Example

CenterControlV( hCtrl )

ForceVisibleDisplay

sub ForceVisibleDisplay( byval hWin as HWND )

Brings back a window that is on no display at all, by centring it in the work area of the display nearest to where it was. A window that is at least partly on some display is left alone.

A program that restores its last position at start-up can open off-screen after the user unplugs or rearranges a monitor. Call this once the window has been created and placed.

Example

SetWindowLocation( hwnd, 5000, 5000 )   ' a saved position, now off every screen
ForceVisibleDisplay( hwnd )

Microsoft Learn: MonitorFromRect

See also

• Category: sys/win
• Display, screen and DPI for the scaling ratios the ForDpi functions use