Bug 1231864 (part 2) - Clean up gfxWindowsNativeDrawing::BeginNativeDrawing(). r=mattwoodrow.

This patch inlines the CurrentSurface() and GetDCWithClip() calls in
BeginNativeDrawing(). This allows them to share a single |cairo_t*| and gets
rid of the GetCairo() call in GetDCWithClip(), which was one of those confusing
ones that only made sense if its a Cairo backend.

The patch also inverts the sense of mDeviceOffset, and changes its type from
gfxPoint to Point.

gfx/thebes/gfxWindowsNativeDrawing.cpp

@@ -15,6 +15,9 @@
 #include "mozilla/gfx/Helpers.h"
 #include "gfx2DGlue.h"
 
+#include "cairo.h"
+#include "cairo-win32.h"
+
 using namespace mozilla;
 using namespace mozilla::gfx;
 
@@ -43,8 +46,21 @@ HDC
 gfxWindowsNativeDrawing::BeginNativeDrawing()
 {
     if (mRenderState == RENDER_STATE_INIT) {
-        RefPtr<gfxASurface> surf =
-          mContext->CurrentSurface(&mDeviceOffset.x, &mDeviceOffset.y);
+        RefPtr<gfxASurface> surf;
+        DrawTarget* drawTarget = mContext->GetDrawTarget();
+        cairo_t* cairo = nullptr;
+        if (drawTarget->GetBackendType() == BackendType::CAIRO) {
+            cairo = static_cast<cairo_t*>
+                (drawTarget->GetNativeSurface(NativeSurfaceType::CAIRO_CONTEXT));
+            if (cairo) {
+                cairo_surface_t* s = cairo_get_target(cairo);
+                if (s) {
+                    mDeviceOffset = mContext->GetDeviceOffset();
+                    surf = gfxASurface::Wrap(s);
+                }
+            }
+        }
+
         if (surf && surf->CairoStatus() != 0)
             return nullptr;
 
@@ -69,7 +85,7 @@ gfxWindowsNativeDrawing::BeginNativeDrawing()
             // grab the DC. This can fail if there is a complex clipping path,
             // in which case we'll have to fall back.
             mWinSurface = static_cast<gfxWindowsSurface*>(static_cast<gfxASurface*>(surf.get()));
-            mDC = mWinSurface->GetDCWithClip(mContext);
+            mDC = cairo_win32_get_dc_with_clip(cairo);
 
             if (mDC) {
                 if (mTransformType == TRANSLATION_ONLY) {
@@ -146,8 +162,8 @@ gfxWindowsNativeDrawing::BeginNativeDrawing()
         }
         GetViewportOrgEx(mDC, &mOrigViewportOrigin);
         SetViewportOrgEx(mDC,
-                         mOrigViewportOrigin.x + (int)mDeviceOffset.x,
-                         mOrigViewportOrigin.y + (int)mDeviceOffset.y,
+                         mOrigViewportOrigin.x - (int)mDeviceOffset.x,
+                         mOrigViewportOrigin.y - (int)mDeviceOffset.y,
                          nullptr);
 
         return mDC;

gfx/thebes/gfxWindowsNativeDrawing.h

@@ -91,7 +91,7 @@ private:
     // what state the rendering is in
     uint8_t mRenderState;
 
-    gfxPoint mDeviceOffset;
+    mozilla::gfx::Point mDeviceOffset;
     RefPtr<gfxPattern> mBlackPattern, mWhitePattern;
 
     enum TransformType {

gfx/thebes/gfxWindowsSurface.cpp

@@ -172,12 +172,6 @@ gfxWindowsSurface::~gfxWindowsSurface()
     }
 }
 
-HDC
-gfxWindowsSurface::GetDCWithClip(gfxContext *ctx)
-{
-    return cairo_win32_get_dc_with_clip (ctx->GetCairo());
-}
-
 HDC
 gfxWindowsSurface::GetDC()
 {

gfx/thebes/gfxWindowsSurface.h

@@ -53,8 +53,6 @@ public:
 
     HDC GetDC();
 
-    HDC GetDCWithClip(gfxContext *);
-
     already_AddRefed<gfxImageSurface> GetAsImageSurface();
 
     nsresult BeginPrinting(const nsAString& aTitle, const nsAString& aPrintToFileName);