Added Windows preferred size code. It doesn't work right now; both GetDC() and GetWindowDC() are not returning at all on both wine and Windows XP; need to debug (print guards are included).

init_windows.go

@@ -66,9 +66,9 @@ func doWindowsInit() (err error) {
 	if err != nil {
 		return fmt.Errorf("error initializing standard window class auxiliary info: %v", err)
 	}
-	err = getStandardWindowsFonts()
+	err = getStandardWindowFonts()
 	if err != nil {
-		return fmt.Errorf("error getting standard Windows fonts: %v", err)
+		return fmt.Errorf("error getting standard window fonts: %v", err)
 	}
 	// TODO others
 	return nil		// all ready to go

prefsize_windows.go

@@ -0,0 +1,156 @@
+// 24 february 2014
+package ui
+
+import (
+//	"syscall"
+	"unsafe"
+)
+
+// For Windows, Microsoft just hands you a list of preferred control sizes as part of the MSDN documentation and tells you to roll with it.
+// These sizes are given in "dialog units", which are independent of the font in use.
+// We need to convert these into standard pixels, which requires we get the device context of the OS window.
+// References:
+// - http://msdn.microsoft.com/en-us/library/windows/desktop/aa511279.aspx#controlsizing for control sizes
+// - http://msdn.microsoft.com/en-us/library/ms645502%28VS.85%29.aspx - the calculation needed
+// - http://support.microsoft.com/kb/125681 - to get the base X and Y
+
+// As we are left with incomplete data, an arbitrary size will be chosen
+const (
+	defaultWidth = 100		// 2 * preferred width of buttons
+)
+
+type dlgunits struct {
+	width	int
+	height	int
+	longest	bool		// TODO actually use this
+}
+
+var stdDlgSizes = [nctypes]dlgunits{
+	c_button:		dlgunits{
+		width:	50,
+		height:	14,
+	},
+	c_checkbox:	dlgunits{
+		// widtdh is not defined here so assume longest
+		longest:	true,
+		height:	10,
+	},
+	c_combobox:	dlgunits{
+		longest:	true,
+		height:	14,
+	},
+	c_lineedit:	dlgunits{
+		longest:	true,
+		height:	14,
+	},
+	c_label:		dlgunits{
+		longest:	true,
+		height:	8,
+	},
+	c_listbox:		dlgunits{
+		longest:	true,
+		// height is not clearly defined here ("an integral number of items (3 items minimum)") so just use a three-line edit control
+		height:	14 + 10 + 10,
+	},
+}
+
+var (
+	_getTextMetrics = user32.NewProc("GetTextMetricsW")
+	_getWindowDC = user32.NewProc("GetWindowDC")
+	_releaseDC = user32.NewProc("ReleaseDC")
+)
+
+func (s *sysData) preferredSize() (width int, height int) {
+println("size of control", s.ctype)
+	var dc _HANDLE
+	var tm _TEXTMETRICS
+	var baseX, baseY int
+
+	ret := make(chan uiret)
+	defer close(ret)
+println("calling getWindowDC")
+	uitask <- &uimsg{
+		call:		_getWindowDC,
+		p:		[]uintptr{uintptr(s.hwnd)},
+		ret:		ret,
+	}
+	r := <-ret
+println("getWindowDC",r.ret,r.err)
+	if r.ret == 0 {		// failure
+		panic(r.err)	// TODO return it instead
+	}
+	dc = _HANDLE(r.ret)
+println("getTextMetrics")
+	uitask <- &uimsg{
+		call:		_getTextMetrics,
+		p:		[]uintptr{
+			uintptr(dc),
+			uintptr(unsafe.Pointer(&tm)),
+		},
+		ret:		ret,
+	}
+	r = <-ret
+println("getTextMetrics",r.ret,r.err)
+	if r.ret == 0 {		// failure
+		panic(r.err)	// TODO return it instead
+	}
+	baseX = int(tm.tmAveCharWidth)		// TODO not optimal; third reference has better way
+	baseY = int(tm.tmHeight)
+println("releaseDC")
+	uitask <- &uimsg{
+		call:		_releaseDC,
+		p:		[]uintptr{
+			uintptr(s.hwnd),
+			uintptr(dc),
+		},
+		ret:		ret,
+	}
+	r = <-ret
+println("releaseDC",r.ret,r.err)
+	if r.ret == 0 {		// failure
+		panic(r.err)	// TODO return it instead
+	}
+
+	// now that we have the conversion factors...
+	width = stdDlgSizes[s.ctype].width
+	if width == 0 {
+		width = defaultWidth
+	}
+	height = stdDlgSizes[s.ctype].height
+	width = muldiv(width, baseX, 4)		// equivalent to right of rect
+	height = muldiv(height, baseY, 8)		// equivalent to bottom of rect
+println("result:", width, height)
+	return width, height
+}
+
+// attempts to mimic the behavior of kernel32.MulDiv()
+// caling it directly would be better (TODO)
+// alternatively TODO make sure the rounding is correct
+func muldiv(ma int, mb int, div int) int {
+	xa := int64(ma) * int64(mb)
+	xa /= int64(div)
+	return int(xa)
+}
+
+type _TEXTMETRICS struct {
+	tmHeight				int32
+	tmAscent				int32
+	tmDescent			int32
+	tmInternalLeading		int32
+	tmExternalLeading		int32
+	tmAveCharWidth		int32
+	tmMaxCharWidth		int32
+	tmWeight				int32
+	tmOverhang			int32
+	tmDigitizedAspectX		int32
+	tmDigitizedAspectY		int32
+	tmFirstChar			uint16
+	tmLastChar			uint16
+	tmDefaultChar			uint16
+	tmBreakChar			uint16
+	tmItalic				byte
+	tmUnderlined			byte
+	tmStruckOut			byte
+	tmPitchAndFamily		byte
+	tmCharSet			byte
+}