From e2ecfdda8c06f6b366dac7744a0319909065ca8d Mon Sep 17 00:00:00 2001
From: Scott Johnson <sjohnson@mozilla.com>
Date: Mon, 15 Oct 2012 14:03:37 -0500
Subject: [PATCH] Bug 784375: Add a preference to control maximum font size
 inflation ratio. [r=dbaron]

---
 layout/base/nsLayoutUtils.cpp                   | 17 ++++++++++++++---
 layout/base/nsLayoutUtils.h                     | 11 ++++++++++-
 .../reftests/font-inflation/maxRatio-1-ref.html | 13 +++++++++++++
 layout/reftests/font-inflation/maxRatio-1.html  | 13 +++++++++++++
 layout/reftests/font-inflation/reftest.list     |  1 +
 modules/libpref/src/init/all.js                 | 13 +++++++++++++
 6 files changed, 64 insertions(+), 4 deletions(-)
 create mode 100644 layout/reftests/font-inflation/maxRatio-1-ref.html
 create mode 100644 layout/reftests/font-inflation/maxRatio-1.html

diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 9e203523788..98297728689 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -106,7 +106,8 @@ typedef FrameMetrics::ViewID ViewID;
 /* static */ uint32_t nsLayoutUtils::sFontSizeInflationEmPerLine;
 /* static */ uint32_t nsLayoutUtils::sFontSizeInflationMinTwips;
 /* static */ uint32_t nsLayoutUtils::sFontSizeInflationLineThreshold;
-/* static */ int32_t nsLayoutUtils::sFontSizeInflationMappingIntercept;
+/* static */ int32_t  nsLayoutUtils::sFontSizeInflationMappingIntercept;
+/* static */ uint32_t nsLayoutUtils::sFontSizeInflationMaxRatio;
 
 static ViewID sScrollIdCounter = FrameMetrics::START_SCROLL_ID;
 
@@ -4739,6 +4740,8 @@ nsLayoutUtils::SizeOfTextRunsForFrames(nsIFrame* aFrame,
 void
 nsLayoutUtils::Initialize()
 {
+  Preferences::AddUintVarCache(&sFontSizeInflationMaxRatio,
+                               "font.size.inflation.maxRatio");
   Preferences::AddUintVarCache(&sFontSizeInflationEmPerLine,
                                "font.size.inflation.emPerLine");
   Preferences::AddUintVarCache(&sFontSizeInflationMinTwips,
@@ -5017,8 +5020,10 @@ nsLayoutUtils::FontSizeInflationInner(const nsIFrame *aFrame,
   }
 
   int32_t interceptParam = nsLayoutUtils::FontSizeInflationMappingIntercept();
+  float maxRatio = (float)nsLayoutUtils::FontSizeInflationMaxRatio() / 100.0f;
 
   float ratio = float(styleFontSize) / float(aMinFontSize);
+  float inflationRatio;
 
   // Given a minimum inflated font size m, a specified font size s, we want to
   // find the inflated font size i and then return the ratio of i to s (i/s).
@@ -5041,12 +5046,18 @@ nsLayoutUtils::FontSizeInflationInner(const nsIFrame *aFrame,
     // graph is a line from (0, m), to that point). We calculate the
     // intersection point to be ((1+P/2)m, (1+P/2)m), where P is the
     // intercept parameter above. We then need to return i/s.
-    return (1.0f + (ratio * (intercept - 1) / intercept)) / ratio;
+    inflationRatio = (1.0f + (ratio * (intercept - 1) / intercept)) / ratio;
   } else {
     // This is the case where P is negative. We essentially want to implement
     // the case for P=infinity here, so we make i = s + m, which means that
     // i/s = s/s + m/s = 1 + 1/ratio
-    return 1 + 1.0f / ratio;
+    inflationRatio = 1 + 1.0f / ratio;
+  }
+
+  if (maxRatio > 1.0 && inflationRatio > maxRatio) {
+    return maxRatio;
+  } else {
+    return inflationRatio;
   }
 }
 
diff --git a/layout/base/nsLayoutUtils.h b/layout/base/nsLayoutUtils.h
index c789d968887..f59512a7b67 100644
--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -1611,6 +1611,14 @@ public:
 
   static bool FontSizeInflationEnabled(nsPresContext *aPresContext);
 
+  /**
+   * See comment above "font.size.inflation.maxRatio" in
+   * modules/libpref/src/init/all.js .
+   */
+  static uint32_t FontSizeInflationMaxRatio() {
+    return sFontSizeInflationMaxRatio;
+  }
+
   /**
    * See comment above "font.size.inflation.emPerLine" in
    * modules/libpref/src/init/all.js .
@@ -1751,7 +1759,8 @@ private:
   static uint32_t sFontSizeInflationEmPerLine;
   static uint32_t sFontSizeInflationMinTwips;
   static uint32_t sFontSizeInflationLineThreshold;
-  static int32_t sFontSizeInflationMappingIntercept;
+  static int32_t  sFontSizeInflationMappingIntercept;
+  static uint32_t sFontSizeInflationMaxRatio;
 };
 
 template<typename PointType, typename RectType, typename CoordType>
diff --git a/layout/reftests/font-inflation/maxRatio-1-ref.html b/layout/reftests/font-inflation/maxRatio-1-ref.html
new file mode 100644
index 00000000000..dce6c6d8e38
--- /dev/null
+++ b/layout/reftests/font-inflation/maxRatio-1-ref.html
@@ -0,0 +1,13 @@
+<!DOCTYPE HTML>
+<style>
+div { background: yellow }
+div { font-size: 24px; width: 450px }
+</style>
+<!--
+In a 450px container, the minimum font size at 15em per line is 30px.
+This means we map 0px-45px into 30px-45px, so 12px gets mapped to 34px.
+However, because we've enabled the maxRatio at a value of 2.0, the mapping
+function, which would normally return 34px/12px, or about 2.83, now
+returns a ratio capped at 2.0, thus the actual font size is 24px.
+-->
+<div>Hello world</div>
diff --git a/layout/reftests/font-inflation/maxRatio-1.html b/layout/reftests/font-inflation/maxRatio-1.html
new file mode 100644
index 00000000000..0cbc120ae9f
--- /dev/null
+++ b/layout/reftests/font-inflation/maxRatio-1.html
@@ -0,0 +1,13 @@
+<!DOCTYPE HTML>
+<style>
+div { background: yellow }
+div { font-size: 12px; width: 450px }
+</style>
+<!--
+In a 450px container, the minimum font size at 15em per line is 30px.
+This means we map 0px-45px into 30px-45px, so 12px gets mapped to 34px.
+However, because we've enabled the maxRatio at a value of 2.0, the mapping
+function, which would normally return 34px/12px, or about 2.83, now
+returns a ratio capped at 2.0, thus the actual font size is 24px.
+-->
+<div>Hello world</div>
diff --git a/layout/reftests/font-inflation/reftest.list b/layout/reftests/font-inflation/reftest.list
index 112a95e3f64..1e16aed3780 100644
--- a/layout/reftests/font-inflation/reftest.list
+++ b/layout/reftests/font-inflation/reftest.list
@@ -5,6 +5,7 @@
 # with the lineThreshold preference explicitly set to zero.  However,
 # newer tests should probably focus more on testing nonzero values of
 # that preference.
+test-pref(font.size.inflation.emPerLine,15) test-pref(font.size.inflation.lineThreshold,0) test-pref(font.size.inflation.maxRatio,200) == maxRatio-1.html maxRatio-1-ref.html
 test-pref(font.size.inflation.emPerLine,15) test-pref(font.size.inflation.lineThreshold,0) == text-1.html text-1-ref.html
 test-pref(font.size.inflation.emPerLine,15) test-pref(font.size.inflation.lineThreshold,0) == text-2.html text-2-ref.html
 test-pref(font.size.inflation.emPerLine,15) test-pref(font.size.inflation.lineThreshold,0) == text-3.html text-3-ref.html
diff --git a/modules/libpref/src/init/all.js b/modules/libpref/src/init/all.js
index 86b2015ab80..bc481862d02 100644
--- a/modules/libpref/src/init/all.js
+++ b/modules/libpref/src/init/all.js
@@ -1816,6 +1816,19 @@ pref("font.size.inflation.lineThreshold", 400);
  */
 pref("font.size.inflation.mappingIntercept", 1);
 
+
+/*
+ * This controls the percentage that fonts will be inflated, if font
+ * size inflation is enabled. Essentially, if we have a specified font
+ * size, s, and an inflated font size, i, this specifies that the ratio
+ * i/s * 100 should never exceed the value of this preference.
+ *
+ * In order for this preference to have any effect, its value must be
+ * greater than 100, since font inflation can never decrease the ratio
+ * i/s.
+ */
+pref("font.size.inflation.maxRatio", 0);
+
 /*
  * When enabled, the touch.radius and mouse.radius prefs allow events to be dispatched
  * to nearby elements that are sensitive to the event. See PositionedEventTargeting.cpp.