Provide approximate type functions for SkMatrix44.

cc/base/math_util_unittest.cc

Index: cc/base/math_util_unittest.cc
diff --git a/cc/base/math_util_unittest.cc b/cc/base/math_util_unittest.cc
index 6e276c25d64736057f975c17ce1b4ee6c08f7c46..0ba9cc1af605d4a17167ab923916f5a8da16808e 100644
--- a/cc/base/math_util_unittest.cc
+++ b/cc/base/math_util_unittest.cc
@@ -5,6 +5,7 @@
 #include "cc/base/math_util.h"
 
 #include <cmath>
+#include <limits>
 
 #include "cc/test/geometry_test_utils.h"
 #include "testing/gmock/include/gmock/gmock.h"
@@ -16,6 +17,32 @@
 namespace cc {
 namespace {
 
+const SkMScalar kApproxZero =
+    SkFloatToMScalar(std::numeric_limits<float>::epsilon());
+const SkMScalar kApproxOne = 1 - kApproxZero;
+
+void SetApproxIdentity(SkMatrix44* matrix) {
+  matrix->set(0, 0, kApproxOne);
+  matrix->set(0, 1, kApproxZero);
+  matrix->set(0, 2, kApproxZero);
+  matrix->set(0, 3, kApproxZero);
+
+  matrix->set(1, 0, kApproxZero);
+  matrix->set(1, 1, kApproxOne);
+  matrix->set(1, 2, kApproxZero);
+  matrix->set(1, 3, kApproxZero);
+
+  matrix->set(2, 0, kApproxZero);
+  matrix->set(2, 1, kApproxZero);
+  matrix->set(2, 2, kApproxOne);
+  matrix->set(2, 3, kApproxZero);
+
+  matrix->set(3, 0, kApproxZero);
+  matrix->set(3, 1, kApproxZero);
+  matrix->set(3, 2, kApproxZero);
+  matrix->set(3, 3, kApproxOne);
+}
+
 TEST(MathUtilTest, ProjectionOfPerpendicularPlane) {
   // In this case, the m33() element of the transform becomes zero, which could
   // cause a divide-by-zero when projecting points/quads.
@@ -120,5 +147,56 @@ TEST(MathUtilTest, VectorProjection) {
             projected_vector.y() / target_vector.y());
 }
 
+TEST(MathUtilTest, ExactPureTranslationMatrix) {
+  SkMatrix44 matrix(SkMatrix44::kIdentity_Constructor);
+
+  // set translate values to values other than 0 or 1
+  matrix.set(0, 3, 3.4);
+  matrix.set(1, 3, 4.4);
+  matrix.set(2, 3, 5.6);
+
+  EXPECT_TRUE(MathUtil::IsMatrixApproximatelyPureTranslation(matrix, 0));
+  EXPECT_TRUE(
+      MathUtil::IsMatrixApproximatelyPureTranslation(matrix, kApproxZero));
+}
+
+TEST(MathUtilTest, ApproximatelyPureTranslationMatrix) {
+  SkMatrix44 matrix(SkMatrix44::kUninitialized_Constructor);
+  SetApproxIdentity(&matrix);
+  // Some values must be exact
+  matrix.set(3, 0, 0);
+  matrix.set(3, 1, 0);
+  matrix.set(3, 2, 0);
+  matrix.set(3, 3, 1);
+
+  // set translate values to values other than 0 or 1
+  matrix.set(0, 3, 3.4);
+  matrix.set(1, 3, 4.4);
+  matrix.set(2, 3, 5.6);
+
+  EXPECT_FALSE(MathUtil::IsMatrixApproximatelyPureTranslation(matrix, 0));

[shawnsingh, 2013/10/16 19:05:37]

nice way to check that we are not accidentally an exact matrix =)  I like it.

+  EXPECT_TRUE(
+      MathUtil::IsMatrixApproximatelyPureTranslation(matrix, kApproxZero));
+}
+
+TEST(MathUtilTest, NotApproximatelyPureTranslationMatrix) {
+  SkMatrix44 matrix(SkMatrix44::kUninitialized_Constructor);
+  SetApproxIdentity(&matrix);
+  // Some values must be exact
+  matrix.set(3, 0, 0);
+  matrix.set(3, 1, 0);
+  matrix.set(3, 2, 0);
+  matrix.set(3, 3, 1);
+
+  // set some values (not translate values) to values other than 0 or 1
+  matrix.set(0, 1, 3.4);
+  matrix.set(3, 2, 4.4);
+  matrix.set(2, 0, 5.6);
+
+  EXPECT_FALSE(MathUtil::IsMatrixApproximatelyPureTranslation(matrix, 0));
+  EXPECT_FALSE(
+      MathUtil::IsMatrixApproximatelyPureTranslation(matrix, kApproxZero));
+}
+
 }  // namespace
 }  // namespace cc