app/internal/windows: don't draw window background on Windows

Avoids flickering between GPU content and the CPU drawn background
color.

gofmt -w -s . now we're here.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/internal/window/os_windows.go

@@ -116,6 +116,7 @@ const (
 	_WM_CREATE      = 0x0001
 	_WM_DPICHANGED  = 0x02E0
 	_WM_DESTROY     = 0x0002
+	_WM_ERASEBKGND  = 0x0014
 	_WM_KEYDOWN     = 0x0100
 	_WM_KEYUP       = 0x0101
 	_WM_LBUTTONDOWN = 0x0201
@@ -273,6 +274,9 @@ func windowProc(hwnd syscall.Handle, msg uint32, wParam, lParam uintptr) uintptr
 	case _WM_DPICHANGED:
 		// Let Windows know we're prepared for runtime DPI changes.
 		return 1
+	case _WM_ERASEBKGND:
+		// Avoid flickering between GPU content and background color.
+		return 1
 	case _WM_KEYDOWN, _WM_SYSKEYDOWN:
 		if n, ok := convertKeyCode(wParam); ok {
 			cmd := key.Event{Name: n}

widget/material/material.go

@@ -24,11 +24,11 @@ type Theme struct {
 		Hint    color.RGBA
 		InvText color.RGBA
 	}
-	TextSize           unit.Value
+	TextSize              unit.Value
 	checkBoxCheckedIcon   *Icon
 	checkBoxUncheckedIcon *Icon
-	radioCheckedIcon   *Icon
-	radioUncheckedIcon *Icon
+	radioCheckedIcon      *Icon
+	radioUncheckedIcon    *Icon
 }
 
 func NewTheme() *Theme {