From 8fb68b79fbd00c9ce833ef0fb6c2cc7e200c1e33 Mon Sep 17 00:00:00 2001
From: Matt Brubeck <mbrubeck@mozilla.com>
Date: Wed, 22 Aug 2012 13:18:10 -0700
Subject: [PATCH] Bug 716575 (3/4) - Move viewport pixel ratio calculations
 into the platform [r=dbaron,jwir3,mfinkle,roc]

---
 content/base/public/nsContentUtils.h |  5 ++
 content/base/src/nsContentUtils.cpp  | 82 +++++++++++++++++++++-------
 2 files changed, 68 insertions(+), 19 deletions(-)

diff --git a/content/base/public/nsContentUtils.h b/content/base/public/nsContentUtils.h
index 907ae89c204..ca4e0dff120 100644
--- a/content/base/public/nsContentUtils.h
+++ b/content/base/public/nsContentUtils.h
@@ -1549,6 +1549,11 @@ public:
                                       uint32_t aDisplayWidth,
                                       uint32_t aDisplayHeight);
 
+  /**
+   * The device-pixel-to-CSS-px ratio used to adjust meta viewport values.
+   */
+  static double GetDevicePixelsPerMetaViewportPixel(nsIWidget* aWidget);
+
   // Call EnterMicroTask when you're entering JS execution.
   // Usually the best way to do this is to use nsAutoMicroTask.
   static void EnterMicroTask() { ++sMicroTaskLevel; }
diff --git a/content/base/src/nsContentUtils.cpp b/content/base/src/nsContentUtils.cpp
index 5d622ccd64f..dc56b99f6d3 100644
--- a/content/base/src/nsContentUtils.cpp
+++ b/content/base/src/nsContentUtils.cpp
@@ -12,6 +12,8 @@
 #include "jsdbgapi.h"
 #include "jsfriendapi.h"
 
+#include <math.h>
+
 #include "Layers.h"
 #include "nsJSUtils.h"
 #include "nsCOMPtr.h"
@@ -5174,12 +5176,44 @@ nsContentUtils::GetViewportInfo(nsIDocument *aDocument,
     autoSize = true;
   }
 
-  uint32_t width = widthStr.ToInteger(&errorCode);
-  if (NS_FAILED(errorCode)) {
-    if (autoSize) {
-      width = aDisplayWidth;
-    } else {
-      width = Preferences::GetInt("browser.viewport.desktopWidth", 0);
+  // Now convert the scale into device pixels per CSS pixel.
+  nsIWidget *widget = WidgetForDocument(aDocument);
+  double pixelRatio = widget ? GetDevicePixelsPerMetaViewportPixel(widget) : 1.0;
+  scaleFloat *= pixelRatio;
+  scaleMinFloat *= pixelRatio;
+  scaleMaxFloat *= pixelRatio;
+
+  uint32_t width, height;
+  if (autoSize) {
+    // aDisplayWidth and aDisplayHeight are in device pixels; convert them to
+    // CSS pixels for the viewport size.
+    width = aDisplayWidth / pixelRatio;
+    height = aDisplayHeight / pixelRatio;
+  } else {
+    nsresult widthErrorCode, heightErrorCode;
+    width = widthStr.ToInteger(&widthErrorCode);
+    height = heightStr.ToInteger(&heightErrorCode);
+
+    // If width or height has not been set to a valid number by this point,
+    // fall back to a default value.
+    bool validWidth = (!widthStr.IsEmpty() && NS_SUCCEEDED(widthErrorCode) && width > 0);
+    bool validHeight = (!heightStr.IsEmpty() && NS_SUCCEEDED(heightErrorCode) && height > 0);
+
+    if (!validWidth) {
+      if (validHeight && aDisplayWidth > 0 && aDisplayHeight > 0) {
+        width = uint32_t((height * aDisplayWidth) / aDisplayHeight);
+      } else {
+        width = Preferences::GetInt("browser.viewport.desktopWidth",
+                                    kViewportDefaultScreenWidth);
+      }
+    }
+
+    if (!validHeight) {
+      if (aDisplayWidth > 0 && aDisplayHeight > 0) {
+        height = uint32_t((width * aDisplayHeight) / aDisplayWidth);
+      } else {
+        height = width;
+      }
     }
   }
 
@@ -5189,19 +5223,7 @@ nsContentUtils::GetViewportInfo(nsIDocument *aDocument,
   // Also recalculate the default zoom, if it wasn't specified in the metadata,
   // and the width is specified.
   if (scaleStr.IsEmpty() && !widthStr.IsEmpty()) {
-    scaleFloat = NS_MAX(scaleFloat, (float)(aDisplayWidth/width));
-  }
-
-  uint32_t height = heightStr.ToInteger(&errorCode);
-
-  if (NS_FAILED(errorCode)) {
-    height = width * ((float)aDisplayHeight / aDisplayWidth);
-  }
-
-  // If height was provided by the user, but width wasn't, then we should
-  // calculate the width.
-  if (widthStr.IsEmpty() && !heightStr.IsEmpty()) {
-    width = (uint32_t) ((height * aDisplayWidth) / aDisplayHeight);
+    scaleFloat = NS_MAX(scaleFloat, float(aDisplayWidth) / float(width));
   }
 
   height = NS_MIN(height, kViewportMaxHeight);
@@ -5237,6 +5259,28 @@ nsContentUtils::GetViewportInfo(nsIDocument *aDocument,
   return ret;
 }
 
+/* static */
+double
+nsContentUtils::GetDevicePixelsPerMetaViewportPixel(nsIWidget* aWidget)
+{
+  int32_t prefValue = Preferences::GetInt("browser.viewport.scaleRatio", 0);
+  if (prefValue > 0) {
+    return double(prefValue) / 100.0;
+  }
+
+  float dpi = aWidget->GetDPI();
+  if (dpi < 200.0) {
+    // Includes desktop displays, LDPI and MDPI Android devices
+    return 1.0;
+  }
+  if (dpi < 300.0) {
+    // Includes Nokia N900, and HDPI Android devices
+    return 1.5;
+  }
+  // For very high-density displays like the iPhone 4, use an integer ratio.
+  return floor(dpi / 150.0);
+}
+
 /* static */
 nsresult
 nsContentUtils::ProcessViewportInfo(nsIDocument *aDocument,