From 382fe423e53a6db2cae7b75d75dca50d3613ac60 Mon Sep 17 00:00:00 2001
From: Moonchild <moonchild@palemoon.org>
Date: Fri, 8 Jan 2021 16:33:36 +0000
Subject: Issue #1705 - Part 7: Implement scrollbar-width:thin on Windows.

---
 widget/windows/nsNativeThemeWin.cpp | 41 +++++++++++++++++++++++++++++--------
 1 file changed, 33 insertions(+), 8 deletions(-)

(limited to 'widget/windows')

diff --git a/widget/windows/nsNativeThemeWin.cpp b/widget/windows/nsNativeThemeWin.cpp
index e84a2b80ce..0947019caa 100644
--- a/widget/windows/nsNativeThemeWin.cpp
+++ b/widget/windows/nsNativeThemeWin.cpp
@@ -1388,6 +1388,12 @@ GetThemeDpiScaleFactor(nsIFrame* aFrame)
   return 1.0;
 }
 
+static bool
+IsScrollbarWidthThin(nsIFrame* aFrame)
+{
+  return aFrame->StyleUserInterface()->mScrollbarWidth == StyleScrollbarWidth::Thin;
+}
+
 NS_IMETHODIMP
 nsNativeThemeWin::DrawWidgetBackground(nsRenderingContext* aContext,
                                        nsIFrame* aFrame,
@@ -2788,14 +2794,21 @@ nsNativeThemeWin::ClassicGetMinimumWidgetSize(nsIFrame* aFrame,
       break;
     case NS_THEME_SCROLLBARBUTTON_UP:
     case NS_THEME_SCROLLBARBUTTON_DOWN:
-      (*aResult).width = ::GetSystemMetrics(SM_CXVSCROLL);
-      (*aResult).height = ::GetSystemMetrics(SM_CYVSCROLL);
+      // Get scrollbar button metrics from the system, except in the case of
+      // thin scrollbars, where we leave them at 0 (collapsing them to invisible)
+      if (!IsScrollbarWidthThin(aFrame)) {
+        (*aResult).width = ::GetSystemMetrics(SM_CXVSCROLL);
+        (*aResult).height = ::GetSystemMetrics(SM_CYVSCROLL);
+      }
       *aIsOverridable = false;
       break;
     case NS_THEME_SCROLLBARBUTTON_LEFT:
     case NS_THEME_SCROLLBARBUTTON_RIGHT:
-      (*aResult).width = ::GetSystemMetrics(SM_CXHSCROLL);
-      (*aResult).height = ::GetSystemMetrics(SM_CYHSCROLL);
+      // See comment above.
+      if (!IsScrollbarWidthThin(aFrame)) {
+        (*aResult).width = ::GetSystemMetrics(SM_CXHSCROLL);
+        (*aResult).height = ::GetSystemMetrics(SM_CYHSCROLL);
+      }
       *aIsOverridable = false;
       break;
     case NS_THEME_SCROLLBAR_VERTICAL:
@@ -2871,8 +2884,14 @@ nsNativeThemeWin::ClassicGetMinimumWidgetSize(nsIFrame* aFrame,
       (*aResult).height = ::GetSystemMetrics(SM_CYVTHUMB);
       // Without theming, divide the thumb size by two in order to look more
       // native
-      if (!GetTheme(aWidgetType))
-        (*aResult).height >>= 1;
+      if (!GetTheme(aWidgetType)) {
+        (*aResult).height /= 2;
+      }
+      // If scrollbar-width is thin, divide the thickness by three to make
+      // it more compact.
+      if (IsScrollbarWidthThin(aFrame)) {
+        (*aResult).width /= 3;
+      }      
       *aIsOverridable = false;
       break;
     case NS_THEME_SCROLLBARTHUMB_HORIZONTAL:
@@ -2880,8 +2899,14 @@ nsNativeThemeWin::ClassicGetMinimumWidgetSize(nsIFrame* aFrame,
       (*aResult).height = ::GetSystemMetrics(SM_CYHSCROLL);
       // Without theming, divide the thumb size by two in order to look more
       // native
-      if (!GetTheme(aWidgetType))
-        (*aResult).width >>= 1;
+      if (!GetTheme(aWidgetType)) {
+        (*aResult).width /= 2;
+      }
+      // If scrollbar-width is thin, divide the thickness by three to make
+      // it more compact.
+      if (IsScrollbarWidthThin(aFrame)) {
+        (*aResult).height /= 3;
+      }      
       *aIsOverridable = false;
       break;
     case NS_THEME_SCROLLBAR_HORIZONTAL:
-- 
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