1 files changed, 121 insertions, 0 deletions
diff --git a/layout/style/StyleStructContext.h b/layout/style/StyleStructContext.h
new file mode 100644
index 000000000..f4b59972e
--- /dev/null
+++ b/layout/style/StyleStructContext.h
@@ -0,0 +1,121 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_StyleStructContext_h
+#define mozilla_StyleStructContext_h
+
+#include "CounterStyleManager.h"
+#include "mozilla/LookAndFeel.h"
+#include "nsPresContext.h"
+
+class nsDeviceContext;
+
+/**
+ * Construction context for style structs.
+ *
+ * Certain Gecko style structs have historically taken an nsPresContext
+ * argument in their constructor, which is used to compute various things. This
+ * makes Gecko style structs document-specific (which Servo style structs are
+ * not), and means that the initial values for style-structs cannot be shared
+ * across the entire runtime (as is the case in Servo).
+ *
+ * We'd like to remove this constraint so that Gecko can get the benefits of the
+ * Servo model, and so that Gecko aligns better with the Servo style system when
+ * using it. Unfortunately, this may require a fair amount of work, especially
+ * related to text zoom.
+ *
+ * So as an intermediate step, we define a reduced API set of "things that are
+ * needed when constructing style structs". This just wraps and forwards to an
+ * nsPresContext in the Gecko case, and returns some default not-always-correct
+ * values in the Servo case. We can then focus on reducing this API surface to
+ * zero, at which point this can be removed.
+ *
+ * We don't put the type in namespace mozilla, since we expect it to be
+ * temporary, and the namespacing would clutter up nsStyleStruct.h.
+ */
+#ifdef MOZ_STYLO
+#define SERVO_DEFAULT(default_val) { if (!mPresContext) { return default_val; } }
+#else
+#define SERVO_DEFAULT(default_val) { MOZ_ASSERT(mPresContext); }
+#endif
+class StyleStructContext {
+public:
+  MOZ_IMPLICIT StyleStructContext(nsPresContext* aPresContext)
+    : mPresContext(aPresContext) { MOZ_ASSERT(aPresContext); }
+  static StyleStructContext ServoContext() { return StyleStructContext(); }
+
+  // XXXbholley: Need to make text zoom work with stylo. This probably means
+  // moving the zoom handling out of computed values and into a post-
+  // computation.
+  float TextZoom()
+  {
+    SERVO_DEFAULT(1.0);
+    return mPresContext->TextZoom();
+  }
+
+  const nsFont* GetDefaultFont(uint8_t aFontID)
+  {
+    // NB: The servo case only differ from the default case in terms of which
+    // font pref cache gets used. The distinction is probably unnecessary.
+    SERVO_DEFAULT(mozilla::StaticPresData::Get()->
+                  GetDefaultFont(aFontID, GetLanguageFromCharset()));
+    return mPresContext->GetDefaultFont(aFontID, GetLanguageFromCharset());
+  }
+
+  uint32_t GetBidi()
+  {
+    SERVO_DEFAULT(0);
+    return mPresContext->GetBidi();
+  }
+
+  int32_t AppUnitsPerDevPixel();
+
+  nscoord DevPixelsToAppUnits(int32_t aPixels)
+  {
+    return NSIntPixelsToAppUnits(aPixels, AppUnitsPerDevPixel());
+  }
+
+  typedef mozilla::LookAndFeel LookAndFeel;
+  nscolor DefaultColor()
+  {
+    SERVO_DEFAULT(LookAndFeel::GetColor(LookAndFeel::eColorID_WindowForeground,
+                                        NS_RGB(0x00, 0x00, 0x00)));
+    return mPresContext->DefaultColor();
+  }
+
+  mozilla::CounterStyle* BuildCounterStyle(const nsSubstring& aName)
+  {
+    SERVO_DEFAULT(mozilla::CounterStyleManager::GetBuiltinStyle(NS_STYLE_LIST_STYLE_DISC));
+    return mPresContext->CounterStyleManager()->BuildCounterStyle(aName);
+  }
+
+  nsIAtom* GetLanguageFromCharset() const
+  {
+    SERVO_DEFAULT(nsGkAtoms::x_western);
+    return mPresContext->GetLanguageFromCharset();
+  }
+
+  already_AddRefed<nsIAtom> GetContentLanguage() const
+  {
+    SERVO_DEFAULT(do_AddRef(nsGkAtoms::x_western));
+    return mPresContext->GetContentLanguage();
+  }
+
+private:
+  nsDeviceContext* DeviceContext()
+  {
+    SERVO_DEFAULT(HackilyFindSomeDeviceContext());
+    return mPresContext->DeviceContext();
+  }
+
+  nsDeviceContext* HackilyFindSomeDeviceContext();
+
+  StyleStructContext() : mPresContext(nullptr) {}
+  nsPresContext* mPresContext;
+};
+
+#undef SERVO_DEFAULT
+
+#endif // mozilla_StyleStructContext_h