Fast loadInverse() implementation for the common case

Most matrices used by the UI toolkit are translation matrices, whose
inverses can be quickly computed by using the negated translation
vector.

Change-Id: I54a28a634a586085779bfc26f3a4160cd5ab2b22

1 files changed, 32 insertions, 4 deletions

diff --git a/libs/hwui/Matrix.cpp b/libs/hwui/Matrix.cpp
index 9f2014f89f46..061d26ab5954 100644
--- a/libs/hwui/Matrix.cpp
+++ b/libs/hwui/Matrix.cpp
@@ -203,6 +203,34 @@ void Matrix4::copyTo(SkMatrix& v) const {
 }
 
 void Matrix4::loadInverse(const Matrix4& v) {
+    // Fast case for common translation matrices
+    if (v.isPureTranslate()) {
+        // Reset the matrix
+        // Unnamed fields are never written to except by
+        // loadIdentity(), they don't need to be reset
+        data[kScaleX]       = 1.0f;
+        data[kSkewX]        = 0.0f;
+
+        data[kScaleY]       = 1.0f;
+        data[kSkewY]        = 0.0f;
+
+        data[kScaleZ]       = 1.0f;
+
+        data[kPerspective0] = 0.0f;
+        data[kPerspective1] = 0.0f;
+        data[kPerspective2] = 1.0f;
+
+        // No need to deal with kTranslateZ because isPureTranslate()
+        // only returns true when the kTranslateZ component is 0
+        data[kTranslateX]   = -v.data[kTranslateX];
+        data[kTranslateY]   = -v.data[kTranslateY];
+        data[kTranslateZ]   = 0.0f;
+
+        // A "pure translate" matrix can be identity or translation
+        mType = v.getType();
+        return;
+    }
+
     double scale = 1.0 /
             (v.data[kScaleX] * ((double) v.data[kScaleY]  * v.data[kPerspective2] -
                     (double) v.data[kTranslateY] * v.data[kPerspective1]) +
@@ -212,18 +240,18 @@ void Matrix4::loadInverse(const Matrix4& v) {
                      (double) v.data[kScaleY] * v.data[kPerspective0]));
 
     data[kScaleX] = (v.data[kScaleY] * v.data[kPerspective2] -
-            v.data[kTranslateY] * v.data[kPerspective1])  * scale;
+            v.data[kTranslateY] * v.data[kPerspective1]) * scale;
     data[kSkewX] = (v.data[kTranslateX] * v.data[kPerspective1] -
             v.data[kSkewX]  * v.data[kPerspective2]) * scale;
     data[kTranslateX] = (v.data[kSkewX] * v.data[kTranslateY] -
-            v.data[kTranslateX] * v.data[kScaleY])  * scale;
+            v.data[kTranslateX] * v.data[kScaleY]) * scale;
 
     data[kSkewY] = (v.data[kTranslateY] * v.data[kPerspective0] -
             v.data[kSkewY]  * v.data[kPerspective2]) * scale;
     data[kScaleY] = (v.data[kScaleX] * v.data[kPerspective2] -
-            v.data[kTranslateX] * v.data[kPerspective0])  * scale;
+            v.data[kTranslateX] * v.data[kPerspective0]) * scale;
     data[kTranslateY] = (v.data[kTranslateX] * v.data[kSkewY] -
-            v.data[kScaleX]  * v.data[kTranslateY]) * scale;
+            v.data[kScaleX] * v.data[kTranslateY]) * scale;
 
     data[kPerspective0] = (v.data[kSkewY] * v.data[kPerspective1] -
             v.data[kScaleY] * v.data[kPerspective0]) * scale;