Re-implement QGraphicsTransform to use QMatrix4x4

QTransform-based transformations create problems when performing
X and Y axis rotations because they aren't using true 3D.  This
change modifies QGraphicsTransform and its sub-classes to use
QMatrix4x4 as the standard transformation matrix, with a project()
function to project back to 2D when required.

Reviewed-by: trustme

1 files changed, 109 insertions, 32 deletions

diff --git a/tests/auto/qgraphicstransform/tst_qgraphicstransform.cpp b/tests/auto/qgraphicstransform/tst_qgraphicstransform.cpp
index bfd346b..029c182 100644
--- a/tests/auto/qgraphicstransform/tst_qgraphicstransform.cpp
+++ b/tests/auto/qgraphicstransform/tst_qgraphicstransform.cpp
@@ -84,60 +84,131 @@ void tst_QGraphicsTransform::cleanup()
 {
 }
 
+static QTransform transform2D(const QGraphicsTransform& t)
+{
+    QMatrix4x4 m;
+    t.applyTo(&m);
+    return QGraphicsTransform::project(m);
+}
 
 void tst_QGraphicsTransform::scale()
 {
     QGraphicsScale scale;
-    scale.setOrigin(QPointF(10, 10));
 
-    QTransform t;
+    // check initial conditions
+    QCOMPARE(scale.xScale(), qreal(1));
+    QCOMPARE(scale.yScale(), qreal(1));
+    QCOMPARE(scale.zScale(), qreal(1));
+    QCOMPARE(scale.origin(), QVector3D(0, 0, 0));
+
+    scale.setOrigin(QVector3D(10, 10, 0));
+
+    QCOMPARE(scale.xScale(), qreal(1));
+    QCOMPARE(scale.yScale(), qreal(1));
+    QCOMPARE(scale.zScale(), qreal(1));
+    QCOMPARE(scale.origin(), QVector3D(10, 10, 0));
+
+    QMatrix4x4 t;
     scale.applyTo(&t);
 
-    QCOMPARE(t, QTransform());
-    QCOMPARE(scale.transform(), QTransform());
+    QCOMPARE(t, QMatrix4x4());
+    QCOMPARE(transform2D(scale), QTransform());
 
     scale.setXScale(10);
-    scale.setOrigin(QPointF(0, 0));
+    scale.setOrigin(QVector3D(0, 0, 0));
+
+    QCOMPARE(scale.xScale(), qreal(10));
+    QCOMPARE(scale.yScale(), qreal(1));
+    QCOMPARE(scale.zScale(), qreal(1));
+    QCOMPARE(scale.origin(), QVector3D(0, 0, 0));
 
     QTransform res;
     res.scale(10, 1);
 
-    QCOMPARE(scale.transform(), res);
-    QCOMPARE(scale.transform().map(QPointF(10, 10)), QPointF(100, 10));
+    QCOMPARE(transform2D(scale), res);
+    QCOMPARE(transform2D(scale).map(QPointF(10, 10)), QPointF(100, 10));
+
+    scale.setOrigin(QVector3D(10, 10, 0));
+    QCOMPARE(transform2D(scale).map(QPointF(10, 10)), QPointF(10, 10));
+    QCOMPARE(transform2D(scale).map(QPointF(11, 10)), QPointF(20, 10));
+
+    scale.setYScale(2);
+    scale.setZScale(4.5);
+    scale.setOrigin(QVector3D(1, 2, 3));
+
+    QCOMPARE(scale.xScale(), qreal(10));
+    QCOMPARE(scale.yScale(), qreal(2));
+    QCOMPARE(scale.zScale(), qreal(4.5));
+    QCOMPARE(scale.origin(), QVector3D(1, 2, 3));
+
+    QMatrix4x4 t2;
+    scale.applyTo(&t2);
 
-    scale.setOrigin(QPointF(10, 10));
-    QCOMPARE(scale.transform().map(QPointF(10, 10)), QPointF(10, 10));
-    QCOMPARE(scale.transform().map(QPointF(11, 10)), QPointF(20, 10));
+    QCOMPARE(t2.map(QVector3D(4, 5, 6)), QVector3D(31, 8, 16.5));
+
+    // Because the origin has a non-zero z, mapping (4, 5) in 2D
+    // will introduce a projective component into the result.
+    QTransform t3 = QGraphicsTransform::project(t2);
+    QCOMPARE(t3.map(QPointF(4, 5)), QPointF(31 / t3.m33(), 8 / t3.m33()));
+}
+
+// QMatrix4x4 uses float internally, whereas QTransform uses qreal.
+// This can lead to issues with qFuzzyCompare() where it uses double
+// precision to compare values that have no more than float precision
+// after conversion from QMatrix4x4 to QTransform.  The following
+// definitions correct for the difference.
+static inline bool fuzzyCompare(qreal p1, qreal p2)
+{
+    return (qAbs(p1 - p2) <= 0.00001f * qMin(qAbs(p1), qAbs(p2)));
+}
+static bool fuzzyCompare(const QTransform& t1, const QTransform& t2)
+{
+    return fuzzyCompare(t1.m11(), t2.m11()) &&
+           fuzzyCompare(t1.m12(), t2.m12()) &&
+           fuzzyCompare(t1.m13(), t2.m13()) &&
+           fuzzyCompare(t1.m21(), t2.m21()) &&
+           fuzzyCompare(t1.m22(), t2.m22()) &&
+           fuzzyCompare(t1.m23(), t2.m23()) &&
+           fuzzyCompare(t1.m31(), t2.m31()) &&
+           fuzzyCompare(t1.m32(), t2.m32()) &&
+           fuzzyCompare(t1.m33(), t2.m33());
 }
 
 void tst_QGraphicsTransform::rotation()
 {
     QGraphicsRotation rotation;
-    QCOMPARE(rotation.axis().x(), (qreal)0);
-    QCOMPARE(rotation.axis().y(), (qreal)0);
-    QCOMPARE(rotation.axis().z(), (qreal)1);
+    QCOMPARE(rotation.axis(), QVector3D(0, 0, 1));
+    QCOMPARE(rotation.origin(), QVector3D(0, 0, 0));
     QCOMPARE(rotation.angle(), (qreal)0);
 
-    rotation.setOrigin(QPointF(10, 10));
+    rotation.setOrigin(QVector3D(10, 10, 0));
+
+    QCOMPARE(rotation.axis(), QVector3D(0, 0, 1));
+    QCOMPARE(rotation.origin(), QVector3D(10, 10, 0));
+    QCOMPARE(rotation.angle(), (qreal)0);
 
-    QTransform t;
+    QMatrix4x4 t;
     rotation.applyTo(&t);
 
-    QCOMPARE(t, QTransform());
-    QCOMPARE(rotation.transform(), QTransform());
+    QCOMPARE(t, QMatrix4x4());
+    QCOMPARE(transform2D(rotation), QTransform());
 
     rotation.setAngle(40);
-    rotation.setOrigin(QPointF(0, 0));
+    rotation.setOrigin(QVector3D(0, 0, 0));
+
+    QCOMPARE(rotation.axis(), QVector3D(0, 0, 1));
+    QCOMPARE(rotation.origin(), QVector3D(0, 0, 0));
+    QCOMPARE(rotation.angle(), (qreal)40);
 
     QTransform res;
     res.rotate(40);
 
-    QCOMPARE(rotation.transform(), res);
+    QVERIFY(fuzzyCompare(transform2D(rotation), res));
 
-    rotation.setOrigin(QPointF(10, 10));
+    rotation.setOrigin(QVector3D(10, 10, 0));
     rotation.setAngle(90);
-    QCOMPARE(rotation.transform().map(QPointF(10, 10)), QPointF(10, 10));
-    QCOMPARE(rotation.transform().map(QPointF(20, 10)), QPointF(10, 20));
+    QCOMPARE(transform2D(rotation).map(QPointF(10, 10)), QPointF(10, 10));
+    QCOMPARE(transform2D(rotation).map(QPointF(20, 10)), QPointF(10, 20));
 }
 
 Q_DECLARE_METATYPE(Qt::Axis);
@@ -161,38 +232,44 @@ void tst_QGraphicsTransform::rotation3d()
     QGraphicsRotation rotation;
     rotation.setAxis(axis);
 
-    QTransform t;
+    QMatrix4x4 t;
     rotation.applyTo(&t);
 
     QVERIFY(t.isIdentity());
-    QVERIFY(rotation.transform().isIdentity());
+    QVERIFY(transform2D(rotation).isIdentity());
 
     rotation.setAngle(angle);
 
+    // QGraphicsRotation uses a correct mathematical rotation in 3D.
+    // QTransform's Qt::YAxis rotation is inverted from the mathematical
+    // version of rotation.  We correct for that here.
     QTransform expected;
-    expected.rotate(angle, axis);
+    if (axis == Qt::YAxis && angle != 180.)
+        expected.rotate(-angle, axis);
+    else
+        expected.rotate(angle, axis);
 
-    QVERIFY(qFuzzyCompare(rotation.transform(), expected));
+    QVERIFY(fuzzyCompare(transform2D(rotation), expected));
 
     //now let's check that a null vector will not change the transform
     rotation.setAxis(QVector3D(0, 0, 0));
-    rotation.setOrigin(QPointF(10, 10));
+    rotation.setOrigin(QVector3D(10, 10, 0));
 
-    t.reset();
+    t.setIdentity();
     rotation.applyTo(&t);
 
     QVERIFY(t.isIdentity());
-    QVERIFY(rotation.transform().isIdentity());
+    QVERIFY(transform2D(rotation).isIdentity());
 
     rotation.setAngle(angle);
 
     QVERIFY(t.isIdentity());
-    QVERIFY(rotation.transform().isIdentity());
+    QVERIFY(transform2D(rotation).isIdentity());
 
-    rotation.setOrigin(QPointF(0, 0));
+    rotation.setOrigin(QVector3D(0, 0, 0));
 
     QVERIFY(t.isIdentity());
-    QVERIFY(rotation.transform().isIdentity());
+    QVERIFY(transform2D(rotation).isIdentity());
 }