Bug 1739699 - Use preferred color scheme when forcing colors with system colors (except windows HCM). r=morgan

This causes (among other things) pages to be dark when using regular
windows system colors and forcing colors to "always", which is nice.

Differential Revision: https://phabricator.services.mozilla.com/D131165

layout/base/nsPresContext.h

@@ -379,6 +379,12 @@ class nsPresContext : public nsISupports, public mozilla::SupportsWeakPtr {
   const mozilla::PreferenceSheet::Prefs& PrefSheetPrefs() const {
     return mozilla::PreferenceSheet::PrefsFor(*mDocument);
   }
+
+  bool ForcingColors() const {
+    return mozilla::PreferenceSheet::MayForceColors() &&
+           !PrefSheetPrefs().mUseDocumentColors;
+  }
+
   nscolor DefaultBackgroundColor() const;
 
   nsISupports* GetContainerWeak() const;

layout/generic/nsBlockFrame.cpp

@@ -7024,8 +7024,7 @@ void nsBlockFrame::BuildDisplayList(nsDisplayListBuilder* aBuilder,
   //    (A) the backplate feature is preffed on
   //    (B) we are not honoring the document colors
   if (StaticPrefs::browser_display_permit_backplate() &&
-      !PresContext()->PrefSheetPrefs().mUseDocumentColors &&
-      !IsComboboxControlFrame()) {
+      PresContext()->ForcingColors() && !IsComboboxControlFrame()) {
     backplateColor.emplace(GetBackplateColor(this));
   }
 

layout/generic/nsCanvasFrame.cpp

@@ -494,7 +494,7 @@ void nsCanvasFrame::BuildDisplayList(nsDisplayListBuilder* aBuilder,
       // conform to their HCM background color when a solid color is rendered,
       // and some websites use solid-color images instead of an overwritable
       // background color.
-      if (!PresContext()->PrefSheetPrefs().mUseDocumentColors &&
+      if (PresContext()->ForcingColors() &&
           StaticPrefs::
               browser_display_suppress_canvas_background_image_on_forced_colors()) {
         return true;

layout/generic/nsIFrame.cpp

@@ -2329,7 +2329,7 @@ already_AddRefed<ComputedStyle> nsIFrame::ComputeSelectionStyle(
   // When in high-contrast mode, the style system ends up ignoring the color
   // declarations, which means that the ::selection style becomes the inherited
   // color, and default background. That's no good.
-  if (!PresContext()->PrefSheetPrefs().mUseDocumentColors) {
+  if (PresContext()->ForcingColors()) {
     return nullptr;
   }
   Element* element = FindElementAncestorForMozSelection(GetContent());

layout/reftests/high-contrast/reftest.list

@@ -87,6 +87,8 @@ test-pref(browser.display.document_color_use,0) == forced-colors-002.html prefer
 == forced-colors-001.html prefers-contrast-black-ref.html
 test-pref(browser.display.document_color_use,0) != forced-colors-001.html prefers-contrast-black-ref.html
 
+pref(browser.display.use_system_colors,true) pref(browser.display.document_color_use,0) test-pref(layout.css.prefers-color-scheme.content-override,0) != about:blank about:blank
+
 != system-colors.html system-colors-notref.html
 
 == border-color-transparent.html border-color-transparent-ref.html

layout/style/PreferenceSheet.h

@@ -89,6 +89,8 @@ struct PreferenceSheet {
     return PrefsKindFor(aDocument) == PrefsKind::Chrome;
   }
 
+  static bool MayForceColors() { return !ContentPrefs().mUseDocumentColors; }
+
   static const Prefs& PrefsFor(const dom::Document& aDocument) {
     switch (PrefsKindFor(aDocument)) {
       case PrefsKind::Chrome:

modules/libpref/init/StaticPrefList.yaml

@@ -1108,7 +1108,7 @@
   mirror: always
 
 - name: browser.display.use_system_colors
-  type: bool
+  type: RelaxedAtomicBool
 #ifdef XP_WIN
   value: true
 #else

servo/components/style/gecko/media_queries.rs

@@ -12,7 +12,8 @@ use crate::gecko_bindings::structs;
 use crate::media_queries::MediaType;
 use crate::properties::ComputedValues;
 use crate::string_cache::Atom;
-use crate::values::computed::Length;
+use crate::values::computed::{Length, ColorScheme};
+use crate::values::specified::color::SystemColor;
 use crate::values::specified::font::FONT_MEDIUM_PX;
 use crate::values::{CustomIdent, KeyframesName};
 use app_units::{Au, AU_PER_PX};
@@ -315,19 +316,28 @@ impl Device {
         self.pref_sheet_prefs().mUseDocumentColors
     }
 
+    /// Computes a system color and returns it as an nscolor.
+    pub(crate) fn system_nscolor(&self, system_color: SystemColor, color_scheme: &ColorScheme) -> u32 {
+        unsafe {
+            bindings::Gecko_ComputeSystemColor(system_color, self.document(), color_scheme)
+        }
+    }
+
     /// Returns the default background color.
     ///
     /// This is only for forced-colors/high-contrast, so looking at light colors
     /// is ok.
-    pub fn default_background_color_for_forced_colors(&self) -> RGBA {
-        convert_nscolor_to_rgba(self.pref_sheet_prefs().mLightColors.mDefaultBackground)
+    pub fn default_background_color(&self) -> RGBA {
+        let normal = ColorScheme::normal();
+        convert_nscolor_to_rgba(self.system_nscolor(SystemColor::Canvas, &normal))
     }
 
     /// Returns the default foreground color.
     ///
     /// See above for looking at light colors only.
-    pub fn default_color_for_forced_colors(&self) -> RGBA {
-        convert_nscolor_to_rgba(self.pref_sheet_prefs().mLightColors.mDefault)
+    pub fn default_color(&self) -> RGBA {
+        let normal = ColorScheme::normal();
+        convert_nscolor_to_rgba(self.system_nscolor(SystemColor::Canvastext, &normal))
     }
 
     /// Returns the current effective text zoom.

servo/components/style/properties/cascade.rs

@@ -437,7 +437,7 @@ fn tweak_when_ignoring_colors(
             // widget background color's rgb channels but not alpha...
             let alpha = alpha_channel(color, context);
             if alpha != 0 {
-                let mut color = context.builder.device.default_background_color_for_forced_colors();
+                let mut color = context.builder.device.default_background_color();
                 color.alpha = alpha;
                 declarations_to_apply_unless_overriden
                     .push(PropertyDeclaration::BackgroundColor(color.into()))
@@ -455,7 +455,7 @@ fn tweak_when_ignoring_colors(
             // override this with a non-transparent color, then override it with
             // the default color. Otherwise just let it inherit through.
             if context.builder.get_parent_inherited_text().clone_color().alpha == 0 {
-                let color = context.builder.device.default_color_for_forced_colors();
+                let color = context.builder.device.default_color();
                 declarations_to_apply_unless_overriden.push(PropertyDeclaration::Color(
                     specified::ColorPropertyValue(color.into()),
                 ))

servo/components/style/values/specified/color.rs

@@ -5,8 +5,6 @@
 //! Specified color values.
 
 use super::AllowQuirks;
-#[cfg(feature = "gecko")]
-use crate::gecko_bindings::structs::nscolor;
 use crate::parser::{Parse, ParserContext};
 use crate::values::computed::{Color as ComputedColor, Context, ToComputedValue};
 use crate::values::generics::color::{GenericCaretColor, GenericColorOrAuto};
@@ -440,18 +438,17 @@ impl SystemColor {
     #[inline]
     fn compute(&self, cx: &Context) -> ComputedColor {
         use crate::gecko_bindings::bindings;
+        use crate::gecko::values::convert_nscolor_to_rgba;
 
         // TODO: We should avoid cloning here most likely, though it's
         // cheap-ish.
         let style_color_scheme =
             cx.style().get_inherited_ui().clone_color_scheme();
-        let color = unsafe {
-            bindings::Gecko_ComputeSystemColor(*self, cx.device().document(), &style_color_scheme)
-        };
+        let color = cx.device().system_nscolor(*self, &style_color_scheme);
         if color == bindings::NS_SAME_AS_FOREGROUND_COLOR {
             return ComputedColor::currentcolor();
         }
-        convert_nscolor_to_computedcolor(color)
+        ComputedColor::rgba(convert_nscolor_to_rgba(color))
     }
 }
 
@@ -718,12 +715,6 @@ impl Color {
     }
 }
 
-#[cfg(feature = "gecko")]
-fn convert_nscolor_to_computedcolor(color: nscolor) -> ComputedColor {
-    use crate::gecko::values::convert_nscolor_to_rgba;
-    ComputedColor::rgba(convert_nscolor_to_rgba(color))
-}
-
 impl Color {
     /// Converts this Color into a ComputedColor.
     ///

widget/nsXPLookAndFeel.cpp

@@ -1121,6 +1121,27 @@ void LookAndFeel::RecomputeColorSchemes() {
 
 ColorScheme LookAndFeel::ColorSchemeForStyle(
     const dom::Document& aDoc, const StyleColorSchemeFlags& aFlags) {
+  if (PreferenceSheet::MayForceColors()) {
+    auto& prefs = PreferenceSheet::PrefsFor(aDoc);
+    if (!prefs.mUseDocumentColors) {
+      // When forcing colors, we can use our preferred color-scheme. Do this
+      // only if we're using system colors, as dark preference colors are not
+      // exposed on the UI.
+      //
+      // Also, use light if we're using a high-contrast-theme on Windows, since
+      // Windows overrides the light colors with HCM colors when HCM is active.
+#ifdef XP_WIN
+      if (prefs.mUseAccessibilityTheme) {
+        return ColorScheme::Light;
+      }
+#endif
+      if (StaticPrefs::browser_display_use_system_colors()) {
+        return aDoc.PreferredColorScheme();
+      }
+      return ColorScheme::Light;
+    }
+  }
+
   StyleColorSchemeFlags style(aFlags);
   if (!style) {
     style.bits = aDoc.GetColorSchemeBits();