Bug 1773633 - Allow configuring OS zoom behavior. r=tnikkel

This is reasonably straight-forward and should allow us change the desired behavior on platforms if / when we need. Also, this adds tests for the feature by using the relevant float pref (though we can't easily assert the full-zoom behavior because it changes the size of the reftest window itself). Differential Revision: https://phabricator.services.mozilla.com/D148902
dothq · Jun 13, 2022 · 3514929 · 3514929
1 parent f35bad6
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Showing 9 changed files with 92 additions and 17 deletions.
diff --git a/dom/base/nsDOMWindowUtils.cpp b/dom/base/nsDOMWindowUtils.cpp
@@ -1877,7 +1877,7 @@ nsDOMWindowUtils::ToScreenRectInCSSUnits(float aX, float aY, float aWidth,
   LayoutDeviceToCSSScale scale = [&] {
     float auPerDev =
         presContext->DeviceContext()->AppUnitsPerDevPixelAtUnitFullZoom();
-    auPerDev /= LookAndFeel::GetTextScaleFactor();
+    auPerDev /= LookAndFeel::SystemZoomSettings().mFullZoom;
     return LayoutDeviceToCSSScale(auPerDev / AppUnitsPerCSSPixel());
   }();
 

diff --git a/layout/base/nsPresContext.cpp b/layout/base/nsPresContext.cpp
@@ -929,16 +929,9 @@ void nsPresContext::RecomputeBrowsingContextDependentData() {
     // matter... Medium also doesn't affect those.
     return;
   }
-  // NOTE(emilio): We use the OS "text scale factor" as an extra source for full
-  // zoom, rather than text zoom (which would seem the obvious choice at first).
-  // is for a variety of reasons:
-  //  * It generally creates more visually consistent results.
-  //  * It has always been the effective behavior on GTK.
-  //  * It matches other browsers as well.
-  float effectiveFullZoom =
-      browsingContext->FullZoom() * LookAndFeel::GetTextScaleFactor();
-  SetFullZoom(effectiveFullZoom);
-  SetTextZoom(browsingContext->TextZoom());
+  auto systemZoom = LookAndFeel::SystemZoomSettings();
+  SetFullZoom(browsingContext->FullZoom() * systemZoom.mFullZoom);
+  SetTextZoom(browsingContext->TextZoom() * systemZoom.mTextZoom);
   SetOverrideDPPX(browsingContext->OverrideDPPX());
 
   auto* top = browsingContext->Top();

diff --git a/layout/reftests/bugs/1773633-full-zoom.html b/layout/reftests/bugs/1773633-full-zoom.html
@@ -0,0 +1,10 @@
+<!doctype html>
+<html reftest-zoom="1.5">
+<style>
+  div {
+    width: 100px;
+    height: 100px;
+    background-color: purple;
+  }
+</style>
+<div>Box with text</div>
diff --git a/layout/reftests/bugs/1773633-text-zoom.html b/layout/reftests/bugs/1773633-text-zoom.html
@@ -0,0 +1,10 @@
+<!doctype html>
+<html reftest-text-zoom="1.5">
+<style>
+  div {
+    width: 100px;
+    height: 100px;
+    background-color: purple;
+  }
+</style>
+<div>Box with text</div>
diff --git a/layout/reftests/bugs/1773633.html b/layout/reftests/bugs/1773633.html
@@ -0,0 +1,9 @@
+<!doctype html>
+<style>
+  div {
+    width: 100px;
+    height: 100px;
+    background-color: purple;
+  }
+</style>
+<div>Box with text</div>
diff --git a/layout/reftests/bugs/reftest.list b/layout/reftests/bugs/reftest.list
@@ -2116,3 +2116,9 @@ pref(image.downscale-during-decode.enabled,true) == 1744468-1.html 1744468-1-ref
 == 1747272-1.html 1747272-1-ref.html
 == 1750146-1.html 1750146-1-ref.html
 == 1735265-1.html 1735265-1-ref.html
+test-pref(ui.textScaleFactor,150) test-pref(browser.display.os-zoom-behavior,0) == 1773633.html 1773633.html
+test-pref(ui.textScaleFactor,150) test-pref(browser.display.os-zoom-behavior,1) != 1773633.html 1773633.html
+test-pref(ui.textScaleFactor,150) test-pref(browser.display.os-zoom-behavior,2) != 1773633.html 1773633.html
+# TODO: This doesn't quite work because textScaleFactor also applies to the reftest window itself, ugh.
+# test-pref(ui.textScaleFactor,150) test-pref(browser.display.os-zoom-behavior,1) == 1773633.html 1773633-full-zoom.html
+test-pref(ui.textScaleFactor,150) test-pref(browser.display.os-zoom-behavior,2) == 1773633.html 1773633-text-zoom.html
diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
@@ -1122,6 +1122,20 @@
   value: "#FBFBFE"
   mirror: never
 
+# Determines the behavior of OS zoom settings.
+#
+#   0: doesn't affect rendering at all
+#   1: affects full zoom (dpi, effectively).
+#   2: affects text zoom.
+#
+# Default is (1): Historical behavior on Linux, matches other browsers on
+# Windows, and generally creates more consistent rendering.
+- name: browser.display.os-zoom-behavior
+  type: RelaxedAtomicInt32
+  value: 1
+  mirror: always
+  rust: true
+
 # Whether focus rings are always shown by default.
 #
 # This is the initial value of nsWindowRoot::mShowFocusRings, but it can be

diff --git a/widget/LookAndFeel.h b/widget/LookAndFeel.h
@@ -446,9 +446,20 @@ class LookAndFeel {
   }
 
   static float GetTextScaleFactor() {
-    return GetFloat(FloatID::TextScaleFactor, 1.0f);
+    float f = GetFloat(FloatID::TextScaleFactor, 1.0f);
+    if (MOZ_UNLIKELY(f <= 0.0f)) {
+      return 1.0f;
+    }
+    return f;
   }
 
+  struct ZoomSettings {
+    float mFullZoom = 1.0f;
+    float mTextZoom = 1.0f;
+  };
+
+  static ZoomSettings SystemZoomSettings();
+
   /**
    * GetInt() and GetFloat() return a int or float value for aID.  The result
    * might be distance, time, some flags or a int value which has particular

diff --git a/widget/nsXPLookAndFeel.cpp b/widget/nsXPLookAndFeel.cpp
@@ -322,6 +322,22 @@ bool nsXPLookAndFeel::sInitialized = false;
 nsXPLookAndFeel* nsXPLookAndFeel::sInstance = nullptr;
 bool nsXPLookAndFeel::sShutdown = false;
 
+auto LookAndFeel::SystemZoomSettings() -> ZoomSettings {
+  ZoomSettings settings;
+  switch (StaticPrefs::browser_display_os_zoom_behavior()) {
+    case 0:
+    default:
+      break;
+    case 1:
+      settings.mFullZoom = GetTextScaleFactor();
+      break;
+    case 2:
+      settings.mTextZoom = GetTextScaleFactor();
+      break;
+  }
+  return settings;
+}
+
 // static
 nsXPLookAndFeel* nsXPLookAndFeel::GetInstance() {
   if (sInstance) {
@@ -385,10 +401,13 @@ static void IntPrefChanged(const nsACString& aPref) {
   LookAndFeel::NotifyChangedAllWindows(changeKind);
 }
 
-static void FloatPrefChanged() {
-  // Float prefs can't change our system colors or fonts.
-  LookAndFeel::NotifyChangedAllWindows(
-      widget::ThemeChangeKind::MediaQueriesOnly);
+static void FloatPrefChanged(const nsACString& aPref) {
+  // Most float prefs can't change our system colors or fonts, but
+  // textScaleFactor affects layout.
+  auto changeKind = aPref.EqualsLiteral("ui.textScaleFactor")
+                        ? widget::ThemeChangeKind::StyleAndLayout
+                        : widget::ThemeChangeKind::MediaQueriesOnly;
+  LookAndFeel::NotifyChangedAllWindows(changeKind);
 }
 
 static void ColorPrefChanged() {
@@ -408,7 +427,7 @@ void nsXPLookAndFeel::OnPrefChanged(const char* aPref, void* aClosure) {
 
   for (const char* pref : sFloatPrefs) {
     if (prefName.Equals(pref)) {
-      FloatPrefChanged();
+      FloatPrefChanged(prefName);
       return;
     }
   }
@@ -434,6 +453,9 @@ static constexpr struct {
     // Affects media queries and scrollbar sizes, so gotta relayout.
     {"widget.gtk.overlay-scrollbars.enabled"_ns,
      widget::ThemeChangeKind::StyleAndLayout},
+    // Affects zoom settings which includes text and full zoom.
+    {"browser.display.os-zoom-behavior"_ns,
+     widget::ThemeChangeKind::StyleAndLayout},
     // This affects not only the media query, but also the native theme, so we
     // need to re-layout.
     {"browser.theme.toolbar-theme"_ns, widget::ThemeChangeKind::AllBits},