From a49417c5ed8357eaf7c1e2084dd46366c3e1213b Mon Sep 17 00:00:00 2001
From: Jeff Muizelaar <jmuizelaar@mozilla.com>
Date: Sat, 2 Dec 2017 13:45:57 -0500
Subject: [PATCH] Bug 1422466. Drop a copy from TextDrawTarget::FillGlyphs.
 r=Gankro

We try hard to ensure that the glyph buffers are of the same type.

--HG--
extra : rebase_source : b785541c15ee2d715b549e0c306e5e0669d4ad71
---
 gfx/layers/wr/WebRenderBridgeChild.cpp |  4 ++--
 gfx/layers/wr/WebRenderBridgeChild.h   |  2 +-
 layout/generic/TextDrawTarget.h        | 28 +++++++++++++++-----------
 3 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/gfx/layers/wr/WebRenderBridgeChild.cpp b/gfx/layers/wr/WebRenderBridgeChild.cpp
index 06fb195b7520..de9664fd1ac3 100644
--- a/gfx/layers/wr/WebRenderBridgeChild.cpp
+++ b/gfx/layers/wr/WebRenderBridgeChild.cpp
@@ -288,7 +288,7 @@ WriteFontDescriptor(const uint8_t* aData, uint32_t aLength, uint32_t aIndex,
 }
 
 void
-WebRenderBridgeChild::PushGlyphs(wr::DisplayListBuilder& aBuilder, const nsTArray<wr::GlyphInstance>& aGlyphs,
+WebRenderBridgeChild::PushGlyphs(wr::DisplayListBuilder& aBuilder, Range<const wr::GlyphInstance> aGlyphs,
                                  gfx::ScaledFont* aFont, const wr::ColorF& aColor, const StackingContextHelper& aSc,
                                  const wr::LayerRect& aBounds, const wr::LayerRect& aClip, bool aBackfaceVisible,
                                  const wr::GlyphOptions* aGlyphOptions)
@@ -304,7 +304,7 @@ WebRenderBridgeChild::PushGlyphs(wr::DisplayListBuilder& aBuilder, const nsTArra
                     aBackfaceVisible,
                     aColor,
                     key,
-                    Range<const wr::GlyphInstance>(aGlyphs.Elements(), aGlyphs.Length()),
+                    aGlyphs,
                     aGlyphOptions);
 }
 
diff --git a/gfx/layers/wr/WebRenderBridgeChild.h b/gfx/layers/wr/WebRenderBridgeChild.h
index 25e5f920f25e..929fd03bb275 100644
--- a/gfx/layers/wr/WebRenderBridgeChild.h
+++ b/gfx/layers/wr/WebRenderBridgeChild.h
@@ -130,7 +130,7 @@ public:
     return wr::WrImageKey{ GetNamespace(), GetNextResourceId() };
   }
 
-  void PushGlyphs(wr::DisplayListBuilder& aBuilder, const nsTArray<wr::GlyphInstance>& aGlyphs,
+  void PushGlyphs(wr::DisplayListBuilder& aBuilder, Range<const wr::GlyphInstance> aGlyphs,
                   gfx::ScaledFont* aFont, const wr::ColorF& aColor,
                   const StackingContextHelper& aSc,
                   const wr::LayerRect& aBounds, const wr::LayerRect& aClip,
diff --git a/layout/generic/TextDrawTarget.h b/layout/generic/TextDrawTarget.h
index 5d0712d57b17..6bb0eeb0b4c4 100644
--- a/layout/generic/TextDrawTarget.h
+++ b/layout/generic/TextDrawTarget.h
@@ -105,8 +105,6 @@ public:
     MOZ_RELEASE_ASSERT(aOptions.mCompositionOp == CompositionOp::OP_OVER);
     MOZ_RELEASE_ASSERT(aOptions.mAlpha == 1.0f);
     MOZ_RELEASE_ASSERT(aPattern.GetType() == PatternType::COLOR);
-    auto* colorPat = static_cast<const ColorPattern*>(&aPattern);
-    auto color = wr::ToColorF(colorPat->mColor);
 
     // Make sure the font exists, and can be serialized
     MOZ_RELEASE_ASSERT(aFont);
@@ -115,17 +113,23 @@ public:
       return;
     }
 
-    // 170 is the maximum size gfxFont is expected to hand us
-    AutoTArray<wr::GlyphInstance, 170> glyphs;
-    glyphs.SetLength(aBuffer.mNumGlyphs);
+    auto* colorPat = static_cast<const ColorPattern*>(&aPattern);
+    auto color = wr::ToColorF(colorPat->mColor);
+    auto glyphs = Range<const wr::GlyphInstance>(reinterpret_cast<const wr::GlyphInstance*>(aBuffer.mGlyphs), aBuffer.mNumGlyphs);
 
-    for (size_t i = 0; i < aBuffer.mNumGlyphs; i++) {
-      wr::GlyphInstance& targetGlyph = glyphs[i];
-      const gfx::Glyph& sourceGlyph = aBuffer.mGlyphs[i];
-      targetGlyph.index = sourceGlyph.mIndex;
-      targetGlyph.point = mSc.ToRelativeLayoutPoint(
-          LayoutDevicePoint::FromUnknownPoint(sourceGlyph.mPosition));
-    }
+    // Compare gfx::Glyph and wr::GlyphInstance to make sure that they are
+    // structurally equivalent to ensure that our cast above was ok
+    static_assert(std::is_same<decltype(aBuffer.mGlyphs[0].mIndex), decltype(glyphs[0].index)>()
+                  && std::is_same<decltype(aBuffer.mGlyphs[0].mPosition.x), decltype(glyphs[0].point.x)>()
+                  && std::is_same<decltype(aBuffer.mGlyphs[0].mPosition.y), decltype(glyphs[0].point.y)>()
+                  && offsetof(std::remove_reference<decltype(aBuffer.mGlyphs[0])>::type, mIndex) == offsetof(wr::GlyphInstance, index)
+                  && offsetof(std::remove_reference<decltype(aBuffer.mGlyphs[0])>::type, mPosition) == offsetof(wr::GlyphInstance, point)
+                  && offsetof(decltype(aBuffer.mGlyphs[0].mPosition), x) == offsetof(decltype(glyphs[0].point), x)
+                  && offsetof(decltype(aBuffer.mGlyphs[0].mPosition), y) == offsetof(decltype(glyphs[0].point), y)
+                  && std::is_standard_layout<decltype(aBuffer.mGlyphs[0])>::value == std::is_standard_layout<decltype(glyphs[0])>::value
+                  && sizeof(aBuffer.mGlyphs[0]) == sizeof(glyphs[0])
+                  && sizeof(aBuffer.mGlyphs[0].mPosition) == sizeof(glyphs[0].point)
+                  , "glyph buf types don't match");
 
     wr::GlyphOptions glyphOptions;
     glyphOptions.render_mode = wr::ToFontRenderMode(aOptions.mAntialiasMode, GetPermitSubpixelAA());