Bug 1688978 - Snap border widths in the non-native theme like we snap layout borders. r=mstange

We might want to snap focus outline widths as well, but that's harder
because it has various segments and separation between them, so we
probably want to snap those separately... So for now only border rects
probably makes sense.

Differential Revision: https://phabricator.services.mozilla.com/D103106

widget/nsNativeBasicTheme.cpp

@@ -43,6 +43,14 @@ struct MOZ_RAII AutoClipRect {
   DrawTarget& mDt;
 };
 
+static LayoutDeviceIntCoord SnapBorderWidth(
+    CSSCoord aCssWidth, nsNativeBasicTheme::DPIRatio aDpiRatio) {
+  if (aCssWidth == 0.0f) {
+    return 0;
+  }
+  return std::max(LayoutDeviceIntCoord(1), (aCssWidth * aDpiRatio).Truncated());
+}
+
 }  // namespace
 
 static bool IsScrollbarWidthThin(nsIFrame* aFrame) {
@@ -483,7 +491,7 @@ void nsNativeBasicTheme::PaintRoundedRect(DrawTarget* aDrawTarget,
                                           CSSCoord aBorderWidth,
                                           RectCornerRadii aDpiAdjustedRadii,
                                           DPIRatio aDpiRatio) {
-  const LayoutDeviceCoord borderWidth(aBorderWidth * aDpiRatio);
+  const LayoutDeviceCoord borderWidth(SnapBorderWidth(aBorderWidth, aDpiRatio));
 
   LayoutDeviceRect rect(aRect);
   // Deflate the rect by half the border width, so that the middle of the stroke
@@ -512,12 +520,11 @@ void nsNativeBasicTheme::PaintCheckboxControl(DrawTarget* aDrawTarget,
                                               const LayoutDeviceRect& aRect,
                                               const EventStates& aState,
                                               DPIRatio aDpiRatio) {
-  const CSSCoord borderWidth = 2.0f;
   const CSSCoord radius = 2.0f;
   auto [backgroundColor, borderColor] =
       ComputeCheckboxColors(aState, StyleAppearance::Checkbox);
   PaintRoundedRectWithRadius(aDrawTarget, aRect, backgroundColor, borderColor,
-                             borderWidth, radius, aDpiRatio);
+                             kCheckboxRadioBorderWidth, radius, aDpiRatio);
 
   if (aState.HasState(NS_EVENT_STATE_FOCUSRING)) {
     PaintRoundedFocusRect(aDrawTarget, aRect, aDpiRatio, 5.0f, 1.0f);
@@ -1342,24 +1349,23 @@ LayoutDeviceIntMargin nsNativeBasicTheme::GetWidgetBorder(
     case StyleAppearance::Textfield:
     case StyleAppearance::Textarea:
     case StyleAppearance::NumberInput: {
-      // FIXME: Do we want this margin not to be int-based? The native windows
-      // theme rounds (see ScaleForDPI)...
-      LayoutDeviceIntCoord w = (kTextFieldBorderWidth * dpiRatio).Rounded();
+      LayoutDeviceIntCoord w = SnapBorderWidth(kTextFieldBorderWidth, dpiRatio);
       return LayoutDeviceIntMargin(w, w, w, w);
     }
     case StyleAppearance::Listbox:
     case StyleAppearance::Menulist:
     case StyleAppearance::MenulistButton: {
-      LayoutDeviceIntCoord w = (kMenulistBorderWidth * dpiRatio).Rounded();
+      LayoutDeviceIntCoord w = SnapBorderWidth(kMenulistBorderWidth, dpiRatio);
       return LayoutDeviceIntMargin(w, w, w, w);
     }
     case StyleAppearance::Button: {
-      LayoutDeviceIntCoord w = (kButtonBorderWidth * dpiRatio).Rounded();
+      LayoutDeviceIntCoord w = SnapBorderWidth(kButtonBorderWidth, dpiRatio);
       return LayoutDeviceIntMargin(w, w, w, w);
     }
     case StyleAppearance::Checkbox:
     case StyleAppearance::Radio: {
-      LayoutDeviceIntCoord w = (kCheckboxRadioBorderWidth * dpiRatio).Rounded();
+      LayoutDeviceIntCoord w =
+          SnapBorderWidth(kCheckboxRadioBorderWidth, dpiRatio);
       return LayoutDeviceIntMargin(w, w, w, w);
     }
     default: