Made the previous commit's changes on Windows. If the Stack Overflow question tells me I'm wrong, we can deal with it then. But yay simple sizing code again :D

redo/sizing_windows.c

@@ -3,29 +3,34 @@
 #include "winapi_windows.h"
 #include "_cgo_export.h"
 
-HDC getDC(HWND hwnd)
+BOOL baseUnitsCalculated = FALSE;
+int baseX;
+int baseY;
+
+/* called by newWindow() so we can calculate base units when we have a window */
+void calculateBaseUnits(HWND hwnd)
 {
 	HDC dc;
+	HFONT prevFont;
+	TEXTMETRICW tm;
 
+	if (baseUnitsCalculated)
+		return;
 	dc = GetDC(hwnd);
 	if (dc == NULL)
 		xpanic("error getting DC for preferred size calculations", GetLastError());
-	/* TODO save for restoring later */
-	if (SelectObject(dc, controlFont) == NULL)
+	prevFont = (HFONT) SelectObject(dc, controlFont);
+	if (prevFont == NULL)
 		xpanic("error loading control font into device context for preferred size calculation", GetLastError());
-	return dc;
-}
-
-void releaseDC(HWND hwnd, HDC dc)
-{
+	if (GetTextMetricsW(dc, &tm) == 0)
+		xpanic("error getting text metrics for preferred size calculations", GetLastError());
+	baseX = (int) tm.tmAveCharWidth;		/* TODO not optimal; third reference below has better way */
+	baseY = (int) tm.tmHeight;
+	if (SelectObject(dc, prevFont) != controlFont)
+		xpanic("error restoring previous font into device context after preferred size calculations", GetLastError());
 	if (ReleaseDC(hwnd, dc) == 0)
 		xpanic("error releasing DC for preferred size calculations", GetLastError());
-}
-
-void getTextMetricsW(HDC dc, TEXTMETRICW *tm)
-{
-	if (GetTextMetricsW(dc, tm) == 0)
-		xpanic("error getting text metrics for preferred size calculations", GetLastError());
+	baseUnitsCalculated = TRUE;
 }
 
 void moveWindow(HWND hwnd, int x, int y, int width, int height)

redo/sizing_windows.go

@@ -21,20 +21,13 @@ const (
 	paddingDialogUnits = 4
 )
 
-// only windows are containers, so only windows get beginResize()
-func (w *window) beginResize() (d *sizing) {
+func (c *container) beginResize() (d *sizing) {
 	d = new(sizing)
 
-	dc := C.getDC(w.hwnd)
-	defer C.releaseDC(w.hwnd, dc)
+	d.baseX = int(C.baseX)
+	d.baseY = int(C.baseY)
 
-	var tm C.TEXTMETRICW
-
-	C.getTextMetricsW(dc, &tm)
-	d.baseX = int(tm.tmAveCharWidth)		// TODO not optimal; third reference below has better way
-	d.baseY = int(tm.tmHeight)
-
-	if w.spaced {
+	if spaced {
 		d.xmargin = int(C.MulDiv(marginDialogUnits, C.int(d.baseX), 4))
 		d.ymargin = int(C.MulDiv(marginDialogUnits, C.int(d.baseY), 8))
 		d.xpadding = int(C.MulDiv(paddingDialogUnits, C.int(d.baseX), 4))

redo/winapi_windows.h

@@ -63,9 +63,10 @@ extern HFONT statusbarFont;
 extern DWORD initWindows(char **);
 
 /* sizing_windows.c */
-extern HDC getDC(HWND);
-extern void releaseDC(HWND, HDC);
-extern void getTextMetricsW(HDC, TEXTMETRICW *);
+extern BOOL baseUnitsCalculated;
+extern int baseX;
+extern int baseY;
+extern void calculateBaseUnits(HWND);
 extern void moveWindow(HWND, int, int, int, int);
 
 /* window_windows.c */

redo/window_windows.c

@@ -73,6 +73,7 @@ HWND newWindow(LPCWSTR title, int width, int height, void *data)
 		NULL, NULL, hInstance, data);
 	if (hwnd == NULL)
 		xpanic("Window creation failed", GetLastError());
+	calculateBaseUnits(hwnd);
 	return hwnd;
 }
 

redo/window_windows.go

@@ -96,7 +96,6 @@ func storeWindowHWND(data unsafe.Pointer, hwnd C.HWND) {
 //export windowResize
 func windowResize(data unsafe.Pointer, r *C.RECT) {
 	w := (*window)(data)
-	w.container.d = w.beginResize()
 	w.resize(int(r.right - r.left), int(r.bottom - r.top))
 }