implement drawAtlas natively on gpu-device

src/core/SkMatrix.cpp

Index: src/core/SkMatrix.cpp
diff --git a/src/core/SkMatrix.cpp b/src/core/SkMatrix.cpp
index 49cffa45f577d7ead8d88316312400c0bddc51df..4f94013d3cec9b8dc80209255b53f5a125a26b00 100644
--- a/src/core/SkMatrix.cpp
+++ b/src/core/SkMatrix.cpp
@@ -1844,11 +1844,26 @@ bool SkDecomposeUpper2x2(const SkMatrix& matrix,
 //////////////////////////////////////////////////////////////////////////////////////////////////
 
 void SkRSXform::toQuad(SkScalar width, SkScalar height, SkPoint quad[4]) const {
+#if 0
+    // This is the slow way, but it documents what we're doing
     quad[0].set(0, 0);
     quad[1].set(width, 0);
     quad[2].set(width, height);
     quad[3].set(0, height);
     SkMatrix m;
     m.setRSXform(*this).mapPoints(quad, quad, 4);
+#else
+    const SkScalar m00 = fSCos;
+    const SkScalar m01 = -fSSin;
+    const SkScalar m02 = fTx;
+    const SkScalar m10 = -m01;
+    const SkScalar m11 = m00;
+    const SkScalar m12 = fTy;
+
+    quad[0].set(m02, m12);
+    quad[1].set(m00 * width + m02, m10 * width + m12);
+    quad[2].set(m00 * width + m01 * height + m02, m10 * width + m11 * height + m12);
+    quad[3].set(m01 * height + m02, m11 * height + m12);
+#endif
 }