From a9767732d1e1e3940443290323b720a4b80cb431 Mon Sep 17 00:00:00 2001
From: Robert O'Callahan <robert@ocallahan.org>
Date: Fri, 13 Aug 2010 21:57:55 +1200
Subject: [PATCH] Bug 537890. Part 2: Get DPI values for Mac, Windows, and X.
 r=jmathies,josh,karlt

---
 widget/src/cocoa/nsChildView.h  |  1 +
 widget/src/cocoa/nsChildView.mm | 22 ++++++++++++++++++++++
 widget/src/gtk2/nsWindow.cpp    | 13 +++++++++++++
 widget/src/gtk2/nsWindow.h      |  1 +
 widget/src/qt/nsWindow.cpp      | 13 +++++++++++++
 widget/src/qt/nsWindow.h        |  1 +
 widget/src/windows/nsWindow.cpp | 16 ++++++++++++++++
 widget/src/windows/nsWindow.h   |  1 +
 8 files changed, 68 insertions(+)

diff --git a/widget/src/cocoa/nsChildView.h b/widget/src/cocoa/nsChildView.h
index 1ac3e04d02a..235920801d1 100644
--- a/widget/src/cocoa/nsChildView.h
+++ b/widget/src/cocoa/nsChildView.h
@@ -297,6 +297,7 @@ public:
 
   NS_IMETHOD              SetParent(nsIWidget* aNewParent);
   virtual nsIWidget*      GetParent(void);
+  virtual float           GetDPI();
 
   LayerManager*           GetLayerManager();
 
diff --git a/widget/src/cocoa/nsChildView.mm b/widget/src/cocoa/nsChildView.mm
index 5e3eff00505..68aa9101243 100644
--- a/widget/src/cocoa/nsChildView.mm
+++ b/widget/src/cocoa/nsChildView.mm
@@ -965,6 +965,28 @@ nsChildView::GetParent()
   return mParentWidget;
 }
 
+float
+nsChildView::GetDPI()
+{
+  NSWindow* window = [mView window];
+  NSScreen* screen = [window screen];
+  if (!screen)
+    return 96.0f;
+
+  CGDirectDisplayID displayID =
+    [[[screen deviceDescription] objectForKey:@"NSScreenNumber"] intValue];
+  CGFloat heightMM = CGDisplayScreenSize(displayID).height;
+  size_t heightPx = CGDisplayPixelsHigh(displayID);
+  CGFloat scaleFactor = [window userSpaceScaleFactor];
+
+  // Currently we don't do our own scaling to take account
+  // of userSpaceScaleFactor, so every "pixel" we draw is actually
+  // userSpaceScaleFactor screen pixels. So divide the screen height
+  // by userSpaceScaleFactor to get the number of "device pixels"
+  // available.
+  return (heightPx / scaleFactor) / (heightMM / 25.4f);
+}
+
 LayerManager*
 nsChildView::GetLayerManager()
 {
diff --git a/widget/src/gtk2/nsWindow.cpp b/widget/src/gtk2/nsWindow.cpp
index d94bc12519a..958b69a1ef0 100644
--- a/widget/src/gtk2/nsWindow.cpp
+++ b/widget/src/gtk2/nsWindow.cpp
@@ -821,6 +821,19 @@ nsWindow::GetParent(void)
     return mParent;
 }
 
+float
+nsWindow::GetDPI()
+{
+    Display *dpy = GDK_DISPLAY();
+    int defaultScreen = DefaultScreen(dpy);
+    double heightInches = DisplayHeightMM(dpy, defaultScreen)/25.4;
+    if (heightInches < 0.25) {
+        // Something's broken, but we'd better not crash.
+        return 96.0f;
+    }
+    return float(DisplayHeight(dpy, defaultScreen)/heightInches);
+}
+
 NS_IMETHODIMP
 nsWindow::SetParent(nsIWidget *aNewParent)
 {
diff --git a/widget/src/gtk2/nsWindow.h b/widget/src/gtk2/nsWindow.h
index 20cfca19efe..e5689aa7970 100644
--- a/widget/src/gtk2/nsWindow.h
+++ b/widget/src/gtk2/nsWindow.h
@@ -136,6 +136,7 @@ public:
                               nsWidgetInitData *aInitData);
     NS_IMETHOD         Destroy(void);
     virtual nsIWidget *GetParent();
+    virtual float      GetDPI();
     virtual nsresult   SetParent(nsIWidget* aNewParent);
     NS_IMETHOD         SetModal(PRBool aModal);
     NS_IMETHOD         IsVisible(PRBool & aState);
diff --git a/widget/src/qt/nsWindow.cpp b/widget/src/qt/nsWindow.cpp
index b587a366ecc..e68f4d3c5e9 100644
--- a/widget/src/qt/nsWindow.cpp
+++ b/widget/src/qt/nsWindow.cpp
@@ -2189,6 +2189,19 @@ nsWindow::GetParent(void)
     return mParent;
 }
 
+float
+nsWindow::GetDPI()
+{
+    QDesktopWidget* rootWindow = QApplication::desktop();
+    double heightInches = rootWindow->heightMM()/25.4;
+    if (heightInches < 0.25) {
+        // Something's broken, but we'd better not crash.
+        return 96.0f;
+    }
+
+    return float(rootWindow->height()/heightInches);
+}
+
 void
 nsWindow::DispatchActivateEvent(void)
 {
diff --git a/widget/src/qt/nsWindow.h b/widget/src/qt/nsWindow.h
index 2eeab48ff7c..19a84a1bc6f 100644
--- a/widget/src/qt/nsWindow.h
+++ b/widget/src/qt/nsWindow.h
@@ -133,6 +133,7 @@ public:
     NS_IMETHOD         Destroy(void);
     NS_IMETHOD         SetParent(nsIWidget* aNewParent);
     virtual nsIWidget *GetParent(void);
+    virtual float      GetDPI();
     NS_IMETHOD         Show(PRBool aState);
     NS_IMETHOD         SetModal(PRBool aModal);
     NS_IMETHOD         IsVisible(PRBool & aState);
diff --git a/widget/src/windows/nsWindow.cpp b/widget/src/windows/nsWindow.cpp
index 1353c6d1002..d86778bdf9e 100644
--- a/widget/src/windows/nsWindow.cpp
+++ b/widget/src/windows/nsWindow.cpp
@@ -1066,6 +1066,22 @@ nsIWidget* nsWindow::GetParent(void)
   return GetParentWindow(PR_FALSE);
 }
 
+float nsWindow::GetDPI()
+{
+  HDC dc = ::GetDC(mWnd);
+  if (!dc)
+    return 96.0f;
+
+  double heightInches = ::GetDeviceCaps(dc, VERTSIZE)/25.4;
+  int heightPx = ::GetDeviceCaps(dc, VERTRES);
+  ::ReleaseDC(mWnd, dc);
+  if (heightInches < 0.25) {
+    // Something's broken
+    return 96.0f;
+  }
+  return float(heightPx/heightInches);
+}
+
 nsWindow* nsWindow::GetParentWindow(PRBool aIncludeOwner)
 {
   if (mIsTopWidgetWindow) {
diff --git a/widget/src/windows/nsWindow.h b/widget/src/windows/nsWindow.h
index 871a45eadd6..7a252b2b9bf 100644
--- a/widget/src/windows/nsWindow.h
+++ b/widget/src/windows/nsWindow.h
@@ -123,6 +123,7 @@ public:
   NS_IMETHOD              Destroy();
   NS_IMETHOD              SetParent(nsIWidget *aNewParent);
   virtual nsIWidget*      GetParent(void);
+  virtual float           GetDPI();
   NS_IMETHOD              Show(PRBool bState);
   NS_IMETHOD              IsVisible(PRBool & aState);
   NS_IMETHOD              ConstrainPosition(PRBool aAllowSlop, PRInt32 *aX, PRInt32 *aY);