Expand testing of SkMatrix::decomposeScale

Bug: skia:7211
Change-Id: If03ad1d364b33e174d91010ca250cd6c2d2f67c2
Reviewed-on: https://skia-review.googlesource.com/140185
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>

1 files changed, 51 insertions, 5 deletions

diff --git a/tests/MatrixTest.cpp b/tests/MatrixTest.cpp
index 03661dc437..fccbf6d8f5 100644
--- a/tests/MatrixTest.cpp
+++ b/tests/MatrixTest.cpp
@@ -20,7 +20,7 @@ static bool nearly_equal_scalar(SkScalar a, SkScalar b) {
 static bool nearly_equal(const SkMatrix& a, const SkMatrix& b) {
     for (int i = 0; i < 9; i++) {
         if (!nearly_equal_scalar(a[i], b[i])) {
-            SkDebugf("not equal %g %g\n", (float)a[i], (float)b[i]);
+            SkDebugf("matrices not equal [%d] %g %g\n", i, (float)a[i], (float)b[i]);
             return false;
         }
     }
@@ -804,18 +804,56 @@ static void test_matrix_homogeneous(skiatest::Reporter* reporter) {
 
 }
 
-static bool check_decompScale(const SkMatrix& matrix) {
+static bool check_decompScale(const SkMatrix& original) {
     SkSize scale;
     SkMatrix remaining;
 
-    if (!matrix.decomposeScale(&scale, &remaining)) {
+    if (!original.decomposeScale(&scale, &remaining)) {
         return false;
     }
     if (scale.width() <= 0 || scale.height() <= 0) {
         return false;
     }
-    remaining.preScale(scale.width(), scale.height());
-    return nearly_equal(matrix, remaining);
+
+    // First ensure that the decomposition reconstitutes back to the original
+    {
+        SkMatrix reconstituted = remaining;
+
+        // This should be 'preScale' but, due to skbug.com/7211, it is reversed!
+        reconstituted.postScale(scale.width(), scale.height());
+        if (!nearly_equal(original, reconstituted)) {
+            return false;
+        }
+    }
+
+    // Then push some points through both paths and make sure they are the same.
+    static const int kNumPoints = 5;
+    const SkPoint testPts[kNumPoints] = {
+        {  0.0f,  0.0f },
+        {  1.0f,  1.0f },
+        {  1.0f,  0.5f },
+        { -1.0f, -0.5f },
+        { -1.0f,  2.0f }
+    };
+
+    SkPoint v1[kNumPoints];
+    original.mapPoints(v1, testPts, kNumPoints);
+
+    SkPoint v2[kNumPoints];
+    SkMatrix scaleMat = SkMatrix::MakeScale(scale.width(), scale.height());
+
+    // Note, we intend the decomposition to be applied in the order scale and then remainder but,
+    // due to skbug.com/7211, the order is reversed!
+    remaining.mapPoints(v2, testPts, kNumPoints);
+    scaleMat.mapPoints(v2, kNumPoints);
+
+    for (int i = 0; i < kNumPoints; ++i) {
+        if (!SkPointPriv::EqualsWithinTolerance(v1[i], v2[i], 0.00001f)) {
+            return false;
+        }
+    }
+
+    return true;
 }
 
 static void test_decompScale(skiatest::Reporter* reporter) {
@@ -830,6 +868,14 @@ static void test_decompScale(skiatest::Reporter* reporter) {
 
     m.setScale(1, 0);
     REPORTER_ASSERT(reporter, !check_decompScale(m));
+
+    m.setRotate(35, 0, 0);
+    m.preScale(2, 3);
+    REPORTER_ASSERT(reporter, check_decompScale(m));
+
+    m.setRotate(35, 0, 0);
+    m.postScale(2, 3);
+    REPORTER_ASSERT(reporter, check_decompScale(m));
 }
 
 DEF_TEST(Matrix, reporter) {