1 files changed, 38 insertions, 0 deletions
diff --git a/services/surfaceflinger/Transform.cpp b/services/surfaceflinger/Transform.cpp
index aca90e0..315720e 100644
--- a/services/surfaceflinger/Transform.cpp
+++ b/services/surfaceflinger/Transform.cpp
@@ -298,6 +298,44 @@ uint32_t Transform::type() const
     return mType;
 }
 
+Transform Transform::inverse() const {
+    // our 3x3 matrix is always of the form of a 2x2 transformation
+    // followed by a translation: T*M, therefore:
+    // (T*M)^-1 = M^-1 * T^-1
+    Transform result;
+    if (mType <= TRANSLATE) {
+        // 1 0 x
+        // 0 1 y
+        // 0 0 1
+        result = *this;
+        result.mMatrix[2][0] = -result.mMatrix[2][0];
+        result.mMatrix[2][1] = -result.mMatrix[2][1];
+    } else {
+        // a c x
+        // b d y
+        // 0 0 1
+        const mat33& M(mMatrix);
+        const float a = M[0][0];
+        const float b = M[1][0];
+        const float c = M[0][1];
+        const float d = M[1][1];
+        const float x = M[2][0];
+        const float y = M[2][1];
+
+        Transform R, T;
+        const float idet = 1.0 / (a*d - b*c);
+        R.mMatrix[0][0] =  d*idet;    R.mMatrix[0][1] = -c*idet;
+        R.mMatrix[1][0] = -b*idet;    R.mMatrix[1][1] =  a*idet;
+        R.mType = mType &= ~TRANSLATE;
+
+        T.mMatrix[2][0] = -x;
+        T.mMatrix[2][1] = -y;
+        T.mType = TRANSLATE;
+        result =  R * T;
+    }
+    return result;
+}
+
 uint32_t Transform::getType() const {
     return type() & 0xFF;
 }