SkMatrix44::preserves2dAxisAlignment()

tests/Matrix44Test.cpp

Index: tests/Matrix44Test.cpp
diff --git a/tests/Matrix44Test.cpp b/tests/Matrix44Test.cpp
index 443086dbef5a298c394e5aa230586231b2fb5bff..3bb4c5591e3cc9c18b5d4c794f01bfcd22f9b9ab 100644
--- a/tests/Matrix44Test.cpp
+++ b/tests/Matrix44Test.cpp
@@ -521,6 +521,226 @@ static void test_3x3_conversion(skiatest::Reporter* reporter) {
     REPORTER_ASSERT(reporter, nearly_equal_scalar(vec4transformed[3], vec4transformed2[3]));
 }
 
+static bool is_rectilinear (SkVector4& p1, SkVector4& p2, SkVector4& p3, SkVector4& p4) {
+    return (p1.fData[0] == p2.fData[0] && p2.fData[1] == p3.fData[1] &&

[danakj, 2014/09/03 19:59:22]

The gfx unit test uses within-std::epsilon<float> for this comparison, but I
guess that can't be the reason for the difference, as that would make yours
report fewer things as preserves, not more.

+            p3.fData[0] == p4.fData[0] && p4.fData[1] == p1.fData[1]) ||
+           (p1.fData[1] == p2.fData[1] && p2.fData[0] == p3.fData[0] &&
+            p3.fData[1] == p4.fData[1] && p4.fData[0] == p1.fData[0]);
+}
+
+static bool empirically_preserves_2d_axis_alignment(skiatest::Reporter* reporter,
+                                                    const SkMatrix44& transform) {
+  SkVector4 p1(5.0f, 5.0f, 0.0f);
+  SkVector4 p2(10.0f, 5.0f, 0.0f);
+  SkVector4 p3(10.0f, 20.0f, 0.0f);
+  SkVector4 p4(5.0f, 20.0f, 0.0f);
+
+  REPORTER_ASSERT(reporter, is_rectilinear(p1, p2, p3, p4));
+
+  p1 = transform * p1;

[danakj, 2014/09/03 19:59:22]

The gfx TransformPoint() method does something more/different than this:

https://code.google.com/p/chromium/codesearch#chromium/src/ui/gfx/transform.c...

Is that the difference? Have you tried printing out the 4 points final values in
this case in that test?

I suspect it's that because a rotate Y could cause clipping with the viewport.

[Ian Vollick, 2014/09/05 15:05:27]

I wonder if dividing through by w to get the perspective effects would help?

+  p2 = transform * p2;
+  p3 = transform * p3;
+  p4 = transform * p4;
+
+SkDebugf("p1 %f %f %f %f\n", p1.fData[0], p1.fData[1], p1.fData[2], p1.fData[3]);
+SkDebugf("p2 %f %f %f %f\n", p2.fData[0], p2.fData[1], p2.fData[2], p2.fData[3]);
+SkDebugf("p3 %f %f %f %f\n", p3.fData[0], p3.fData[1], p3.fData[2], p3.fData[3]);
+SkDebugf("p4 %f %f %f %f\n", p4.fData[0], p4.fData[1], p4.fData[2], p4.fData[3]);
+
+  return is_rectilinear(p1, p2, p3, p4);
+}
+
+static void test_preserves_2d_axis_alignment(skiatest::Reporter* reporter) {
+  SkMatrix44 transform(SkMatrix44::kUninitialized_Constructor);
+  SkMatrix44 transform2(SkMatrix44::kUninitialized_Constructor);
+
+/*
+  static const struct TestCase {
+    SkMScalar a; // row 1, column 1
+    SkMScalar b; // row 1, column 2
+    SkMScalar c; // row 2, column 1
+    SkMScalar d; // row 2, column 2
+    bool expected;
+  } test_cases[] = {
+    { 3.f, 0.f,
+      0.f, 4.f, true }, // basic case
+    { 0.f, 4.f,
+      3.f, 0.f, true }, // rotate by 90
+    { 0.f, 0.f,
+      0.f, 4.f, true }, // degenerate x
+    { 3.f, 0.f,
+      0.f, 0.f, true }, // degenerate y
+    { 0.f, 0.f,
+      3.f, 0.f, true }, // degenerate x + rotate by 90
+    { 0.f, 4.f,
+      0.f, 0.f, true }, // degenerate y + rotate by 90
+    { 3.f, 4.f,
+      0.f, 0.f, false },
+    { 0.f, 0.f,
+      3.f, 4.f, false },
+    { 0.f, 3.f,
+      0.f, 4.f, false },
+    { 3.f, 0.f,
+      4.f, 0.f, false },
+    { 3.f, 4.f,
+      5.f, 0.f, false },
+    { 3.f, 4.f,
+      0.f, 5.f, false },
+    { 3.f, 0.f,
+      4.f, 5.f, false },
+    { 0.f, 3.f,
+      4.f, 5.f, false },
+    { 2.f, 3.f,
+      4.f, 5.f, false },
+  };
+
+  for (size_t i = 0; i < sizeof(test_cases)/sizeof(TestCase); ++i) {
+    const TestCase& value = test_cases[i];
+    transform.setIdentity();
+    transform.set(0, 0, value.a);
+    transform.set(0, 1, value.b);
+    transform.set(1, 0, value.c);
+    transform.set(1, 1, value.d);
+
+    if (value.expected) {
+      REPORTER_ASSERT(reporter, empirically_preserves_2d_axis_alignment(reporter, transform));
+      REPORTER_ASSERT(reporter, transform.preserves2dAxisAlignment());
+    } else {
+      REPORTER_ASSERT(reporter, !empirically_preserves_2d_axis_alignment(reporter, transform));
+      REPORTER_ASSERT(reporter, !transform.preserves2dAxisAlignment());
+    }
+  }
+
+  // Try the same test cases again, but this time make sure that other matrix
+  // elements (except perspective) have entries, to test that they are ignored.
+  for (size_t i = 0; i < sizeof(test_cases)/sizeof(TestCase); ++i) {
+    const TestCase& value = test_cases[i];
+    transform.setIdentity();
+    transform.set(0, 0, value.a);
+    transform.set(0, 1, value.b);
+    transform.set(1, 0, value.c);
+    transform.set(1, 1, value.d);
+
+    transform.set(0, 2, 1.f);
+    transform.set(0, 3, 2.f);
+    transform.set(1, 2, 3.f);
+    transform.set(1, 3, 4.f);
+    transform.set(2, 0, 5.f);
+    transform.set(2, 1, 6.f);
+    transform.set(2, 2, 7.f);
+    transform.set(2, 3, 8.f);
+
+    if (value.expected) {
+      REPORTER_ASSERT(reporter, empirically_preserves_2d_axis_alignment(reporter, transform));
+      REPORTER_ASSERT(reporter, transform.preserves2dAxisAlignment());
+    } else {
+      REPORTER_ASSERT(reporter, !empirically_preserves_2d_axis_alignment(reporter, transform));
+      REPORTER_ASSERT(reporter, !transform.preserves2dAxisAlignment());
+    }
+  }
+
+  // Try the same test cases again, but this time add perspective which is
+  // always assumed to not-preserve axis alignment.
+  for (size_t i = 0; i < sizeof(test_cases)/sizeof(TestCase); ++i) {
+    const TestCase& value = test_cases[i];
+    transform.setIdentity();
+    transform.set(0, 0, value.a);
+    transform.set(0, 1, value.b);
+    transform.set(1, 0, value.c);
+    transform.set(1, 1, value.d);
+
+    transform.set(0, 2, 1.f);
+    transform.set(0, 3, 2.f);
+    transform.set(1, 2, 3.f);
+    transform.set(1, 3, 4.f);
+    transform.set(2, 0, 5.f);
+    transform.set(2, 1, 6.f);
+    transform.set(2, 2, 7.f);
+    transform.set(2, 3, 8.f);
+    transform.set(3, 0, 9.f);
+    transform.set(3, 1, 10.f);
+    transform.set(3, 2, 11.f);
+    transform.set(3, 3, 12.f);
+
+    REPORTER_ASSERT(reporter, !empirically_preserves_2d_axis_alignment(reporter, transform));
+    REPORTER_ASSERT(reporter, !transform.preserves2dAxisAlignment());
+  }
+
+  // Try a few more practical situations to check precision
+  transform.setRotateDegreesAbout(0.0, 0.0, 1.0, 90.0);
+  REPORTER_ASSERT(reporter, empirically_preserves_2d_axis_alignment(reporter, transform));
+  REPORTER_ASSERT(reporter, transform.preserves2dAxisAlignment());
+
+  transform.setRotateDegreesAbout(0.0, 0.0, 1.0, 180.0);
+  REPORTER_ASSERT(reporter, empirically_preserves_2d_axis_alignment(reporter, transform));
+  REPORTER_ASSERT(reporter, transform.preserves2dAxisAlignment());
+
+  transform.setRotateDegreesAbout(0.0, 0.0, 1.0, 270.0);
+  REPORTER_ASSERT(reporter, empirically_preserves_2d_axis_alignment(reporter, transform));
+  REPORTER_ASSERT(reporter, transform.preserves2dAxisAlignment());
+
+  transform.setRotateDegreesAbout(0.0, 1.0, 0.0, 90.0);
+  REPORTER_ASSERT(reporter, empirically_preserves_2d_axis_alignment(reporter, transform));
+  REPORTER_ASSERT(reporter, transform.preserves2dAxisAlignment());
+
+  transform.setRotateDegreesAbout(1.0, 0.0, 0.0, 90.0);
+  REPORTER_ASSERT(reporter, empirically_preserves_2d_axis_alignment(reporter, transform));
+  REPORTER_ASSERT(reporter, transform.preserves2dAxisAlignment());
+
+  transform.setRotateDegreesAbout(0.0, 0.0, 1.0, 90.0);
+  transform2.setRotateDegreesAbout(0.0, 1.0, 0.0, 90.0);
+  transform.postConcat(transform2);
+  REPORTER_ASSERT(reporter, empirically_preserves_2d_axis_alignment(reporter, transform));
+  REPORTER_ASSERT(reporter, transform.preserves2dAxisAlignment());
+
+  transform.setRotateDegreesAbout(0.0, 0.0, 1.0, 90.0);
+  transform2.setRotateDegreesAbout(1.0, 0.0, 0.0, 90.0);
+  transform.postConcat(transform2);
+  REPORTER_ASSERT(reporter, empirically_preserves_2d_axis_alignment(reporter, transform));
+  REPORTER_ASSERT(reporter, transform.preserves2dAxisAlignment());
+
+  transform.setRotateDegreesAbout(0.0, 1.0, 0.0, 90.0);
+  transform2.setRotateDegreesAbout(0.0, 0.0, 1.0, 90.0);
+  transform.postConcat(transform2);
+  REPORTER_ASSERT(reporter, empirically_preserves_2d_axis_alignment(reporter, transform));
+  REPORTER_ASSERT(reporter, transform.preserves2dAxisAlignment());
+
+  transform.setRotateDegreesAbout(0.0, 0.0, 1.0, 45.0);
+  REPORTER_ASSERT(reporter, !empirically_preserves_2d_axis_alignment(reporter, transform));
+  REPORTER_ASSERT(reporter, !transform.preserves2dAxisAlignment());
+
+  // 3-d case; In 2d after an orthographic projection, this case does
+  // preserve 2d axis alignment. But in 3d, it does not preserve axis
+  // alignment.
+  transform.setRotateDegreesAbout(0.0, 1.0, 0.0, 45.0);
+  REPORTER_ASSERT(reporter, empirically_preserves_2d_axis_alignment(reporter, transform));
+  REPORTER_ASSERT(reporter, transform.preserves2dAxisAlignment());
+
+  transform.setRotateDegreesAbout(1.0, 0.0, 0.0, 45.0);
+  REPORTER_ASSERT(reporter, empirically_preserves_2d_axis_alignment(reporter, transform));
+  REPORTER_ASSERT(reporter, transform.preserves2dAxisAlignment());
+*/
+
+  // Perspective cases.
+  transform.setIdentity();
+  transform.set(3, 2, -0.1);
+  transform2.setRotateDegreesAbout(0.0, 1.0, 0.0, 45.0);
+  transform.preConcat(transform2);
+
+transform.dump();
+
+  REPORTER_ASSERT(reporter, !empirically_preserves_2d_axis_alignment(reporter, transform));
+  REPORTER_ASSERT(reporter, !transform.preserves2dAxisAlignment());
+
+  transform.setIdentity();
+  transform.set(3, 2, -0.1);
+  transform2.setRotateDegreesAbout(0.0, 0.0, 1.0, 90.0);
+  transform.preConcat(transform2);
+  REPORTER_ASSERT(reporter, empirically_preserves_2d_axis_alignment(reporter, transform));
+  REPORTER_ASSERT(reporter, transform.preserves2dAxisAlignment());
+}
+
+
 DEF_TEST(Matrix44, reporter) {
     SkMatrix44 mat(SkMatrix44::kUninitialized_Constructor);
     SkMatrix44 inverse(SkMatrix44::kUninitialized_Constructor);
@@ -626,4 +846,5 @@ DEF_TEST(Matrix44, reporter) {
     test_scale(reporter);
     test_map2(reporter);
     test_3x3_conversion(reporter);
+    test_preserves_2d_axis_alignment(reporter);
 }