Make gui/math3d classes use float rather than qreal

This corrects the mismatch between using floats for internal storage
and qreal in the API of QVector*D which leads to lots of implicit
casts between double and float.

This change also stops users from being surprised by the loss of
precision when using these classes on desktop platforms and removes
the need for the private constructors taking a dummy int as the final
argument.

The QMatrix4x4 and QQuaternion classes have been changed to use float
for their internal storage since these are meant to be used in
conjunction with the QVector*D classes. This is to prevent unexpected
loss of precision and to improve performance.

The on-disk format has also been changed from double to float thereby
reducing the storage required when streaming vectors and matrices. This
is potentially a large saving when working with complex 3D meshes etc.

This also has a significant performance improvement when passing
matrices to QOpenGLShaderProgram (and QGLShaderProgram) as we no
longer have to iterate and convert the data to floats. This is
an operation that could easily be needed many times per frame.

This change also opens the door for further optimisations of these
classes to be implemented by using SIMD intrinsics.

This needs to be applied in conjunction with

https://codereview.qt-project.org/#change,33548

Task-number: QTBUG-21035
Task-number: QTBUG-20661
Change-Id: I9321b06040ffb93ae1cbd72fd2013267ac901b2e
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>

1 files changed, 50 insertions, 45 deletions

diff --git a/src/gui/math3d/qvector4d.cpp b/src/gui/math3d/qvector4d.cpp
index a188333a3a..81eedaedb0 100644
--- a/src/gui/math3d/qvector4d.cpp
+++ b/src/gui/math3d/qvector4d.cpp
@@ -61,11 +61,6 @@ QT_BEGIN_NAMESPACE
     The QVector4D class can also be used to represent vertices in 4D space.
     We therefore do not need to provide a separate vertex class.
 
-    \b{Note:} By design values in the QVector4D instance are stored as \c float.
-    This means that on platforms where the \c qreal arguments to QVector4D
-    functions are represented by \c double values, it is possible to
-    lose precision.
-
     \sa QQuaternion, QVector2D, QVector3D
 */
 
@@ -76,7 +71,7 @@ QT_BEGIN_NAMESPACE
 */
 
 /*!
-    \fn QVector4D::QVector4D(qreal xpos, qreal ypos, qreal zpos, qreal wpos)
+    \fn QVector4D::QVector4D(float xpos, float ypos, float zpos, float wpos)
 
     Constructs a vector with coordinates (\a xpos, \a ypos, \a zpos, \a wpos).
 */
@@ -117,7 +112,7 @@ QVector4D::QVector4D(const QVector2D& vector)
 
     \sa toVector2D()
 */
-QVector4D::QVector4D(const QVector2D& vector, qreal zpos, qreal wpos)
+QVector4D::QVector4D(const QVector2D& vector, float zpos, float wpos)
 {
     xp = vector.xp;
     yp = vector.yp;
@@ -149,7 +144,7 @@ QVector4D::QVector4D(const QVector3D& vector)
 
     \sa toVector3D()
 */
-QVector4D::QVector4D(const QVector3D& vector, qreal wpos)
+QVector4D::QVector4D(const QVector3D& vector, float wpos)
 {
     xp = vector.xp;
     yp = vector.yp;
@@ -167,7 +162,7 @@ QVector4D::QVector4D(const QVector3D& vector, qreal wpos)
 */
 
 /*!
-    \fn qreal QVector4D::x() const
+    \fn float QVector4D::x() const
 
     Returns the x coordinate of this point.
 
@@ -175,7 +170,7 @@ QVector4D::QVector4D(const QVector3D& vector, qreal wpos)
 */
 
 /*!
-    \fn qreal QVector4D::y() const
+    \fn float QVector4D::y() const
 
     Returns the y coordinate of this point.
 
@@ -183,7 +178,7 @@ QVector4D::QVector4D(const QVector3D& vector, qreal wpos)
 */
 
 /*!
-    \fn qreal QVector4D::z() const
+    \fn float QVector4D::z() const
 
     Returns the z coordinate of this point.
 
@@ -191,7 +186,7 @@ QVector4D::QVector4D(const QVector3D& vector, qreal wpos)
 */
 
 /*!
-    \fn qreal QVector4D::w() const
+    \fn float QVector4D::w() const
 
     Returns the w coordinate of this point.
 
@@ -199,7 +194,7 @@ QVector4D::QVector4D(const QVector3D& vector, qreal wpos)
 */
 
 /*!
-    \fn void QVector4D::setX(qreal x)
+    \fn void QVector4D::setX(float x)
 
     Sets the x coordinate of this point to the given \a x coordinate.
 
@@ -207,7 +202,7 @@ QVector4D::QVector4D(const QVector3D& vector, qreal wpos)
 */
 
 /*!
-    \fn void QVector4D::setY(qreal y)
+    \fn void QVector4D::setY(float y)
 
     Sets the y coordinate of this point to the given \a y coordinate.
 
@@ -215,7 +210,7 @@ QVector4D::QVector4D(const QVector3D& vector, qreal wpos)
 */
 
 /*!
-    \fn void QVector4D::setZ(qreal z)
+    \fn void QVector4D::setZ(float z)
 
     Sets the z coordinate of this point to the given \a z coordinate.
 
@@ -223,7 +218,7 @@ QVector4D::QVector4D(const QVector3D& vector, qreal wpos)
 */
 
 /*!
-    \fn void QVector4D::setW(qreal w)
+    \fn void QVector4D::setW(float w)
 
     Sets the w coordinate of this point to the given \a w coordinate.
 
@@ -235,9 +230,14 @@ QVector4D::QVector4D(const QVector3D& vector, qreal wpos)
 
     \sa lengthSquared(), normalized()
 */
-qreal QVector4D::length() const
+float QVector4D::length() const
 {
-    return qSqrt(xp * xp + yp * yp + zp * zp + wp * wp);
+    // Need some extra precision if the length is very small.
+    double len = double(xp) * double(xp) +
+                 double(yp) * double(yp) +
+                 double(zp) * double(zp) +
+                 double(wp) * double(wp);
+    return float(sqrt(len));
 }
 
 /*!
@@ -246,7 +246,7 @@ qreal QVector4D::length() const
 
     \sa length(), dotProduct()
 */
-qreal QVector4D::lengthSquared() const
+float QVector4D::lengthSquared() const
 {
     return xp * xp + yp * yp + zp * zp + wp * wp;
 }
@@ -267,12 +267,17 @@ QVector4D QVector4D::normalized() const
                  double(yp) * double(yp) +
                  double(zp) * double(zp) +
                  double(wp) * double(wp);
-    if (qFuzzyIsNull(len - 1.0f))
+    if (qFuzzyIsNull(len - 1.0f)) {
         return *this;
-    else if (!qFuzzyIsNull(len))
-        return *this / qSqrt(len);
-    else
+    } else if (!qFuzzyIsNull(len)) {
+        double sqrtLen = sqrt(len);
+        return QVector4D(float(double(xp) / sqrtLen),
+                         float(double(yp) / sqrtLen),
+                         float(double(zp) / sqrtLen),
+                         float(double(wp) / sqrtLen));
+    } else {
         return QVector4D();
+    }
 }
 
 /*!
@@ -291,12 +296,12 @@ void QVector4D::normalize()
     if (qFuzzyIsNull(len - 1.0f) || qFuzzyIsNull(len))
         return;
 
-    len = qSqrt(len);
+    len = sqrt(len);
 
-    xp /= len;
-    yp /= len;
-    zp /= len;
-    wp /= len;
+    xp = float(double(xp) / len);
+    yp = float(double(yp) / len);
+    zp = float(double(zp) / len);
+    wp = float(double(wp) / len);
 }
 
 /*!
@@ -318,7 +323,7 @@ void QVector4D::normalize()
 */
 
 /*!
-    \fn QVector4D &QVector4D::operator*=(qreal factor)
+    \fn QVector4D &QVector4D::operator*=(float factor)
 
     Multiplies this vector's coordinates by the given \a factor, and
     returns a reference to this vector.
@@ -334,7 +339,7 @@ void QVector4D::normalize()
 */
 
 /*!
-    \fn QVector4D &QVector4D::operator/=(qreal divisor)
+    \fn QVector4D &QVector4D::operator/=(float divisor)
 
     Divides this vector's coordinates by the given \a divisor, and
     returns a reference to this vector.
@@ -345,7 +350,7 @@ void QVector4D::normalize()
 /*!
     Returns the dot product of \a v1 and \a v2.
 */
-qreal QVector4D::dotProduct(const QVector4D& v1, const QVector4D& v2)
+float QVector4D::dotProduct(const QVector4D& v1, const QVector4D& v2)
 {
     return v1.xp * v2.xp + v1.yp * v2.yp + v1.zp * v2.zp + v1.wp * v2.wp;
 }
@@ -387,7 +392,7 @@ qreal QVector4D::dotProduct(const QVector4D& v1, const QVector4D& v2)
 */
 
 /*!
-    \fn const QVector4D operator*(qreal factor, const QVector4D &vector)
+    \fn const QVector4D operator*(float factor, const QVector4D &vector)
     \relates QVector4D
 
     Returns a copy of the given \a vector,  multiplied by the given \a factor.
@@ -396,7 +401,7 @@ qreal QVector4D::dotProduct(const QVector4D& v1, const QVector4D& v2)
 */
 
 /*!
-    \fn const QVector4D operator*(const QVector4D &vector, qreal factor)
+    \fn const QVector4D operator*(const QVector4D &vector, float factor)
     \relates QVector4D
 
     Returns a copy of the given \a vector,  multiplied by the given \a factor.
@@ -426,7 +431,7 @@ qreal QVector4D::dotProduct(const QVector4D& v1, const QVector4D& v2)
 */
 
 /*!
-    \fn const QVector4D operator/(const QVector4D &vector, qreal divisor)
+    \fn const QVector4D operator/(const QVector4D &vector, float divisor)
     \relates QVector4D
 
     Returns the QVector4D object formed by dividing all four components of
@@ -452,7 +457,7 @@ qreal QVector4D::dotProduct(const QVector4D& v1, const QVector4D& v2)
 */
 QVector2D QVector4D::toVector2D() const
 {
-    return QVector2D(xp, yp, 1);
+    return QVector2D(xp, yp);
 }
 
 /*!
@@ -466,7 +471,7 @@ QVector2D QVector4D::toVector2DAffine() const
 {
     if (qIsNull(wp))
         return QVector2D();
-    return QVector2D(xp / wp, yp / wp, 1);
+    return QVector2D(xp / wp, yp / wp);
 }
 
 #endif
@@ -480,7 +485,7 @@ QVector2D QVector4D::toVector2DAffine() const
 */
 QVector3D QVector4D::toVector3D() const
 {
-    return QVector3D(xp, yp, zp, 1);
+    return QVector3D(xp, yp, zp);
 }
 
 /*!
@@ -493,7 +498,7 @@ QVector3D QVector4D::toVector3DAffine() const
 {
     if (qIsNull(wp))
         return QVector3D();
-    return QVector3D(xp / wp, yp / wp, zp / wp, 1);
+    return QVector3D(xp / wp, yp / wp, zp / wp);
 }
 
 #endif
@@ -550,8 +555,8 @@ QDebug operator<<(QDebug dbg, const QVector4D &vector)
 
 QDataStream &operator<<(QDataStream &stream, const QVector4D &vector)
 {
-    stream << double(vector.x()) << double(vector.y())
-           << double(vector.z()) << double(vector.w());
+    stream << vector.x() << vector.y()
+           << vector.z() << vector.w();
     return stream;
 }
 
@@ -567,15 +572,15 @@ QDataStream &operator<<(QDataStream &stream, const QVector4D &vector)
 
 QDataStream &operator>>(QDataStream &stream, QVector4D &vector)
 {
-    double x, y, z, w;
+    float x, y, z, w;
     stream >> x;
     stream >> y;
     stream >> z;
     stream >> w;
-    vector.setX(qreal(x));
-    vector.setY(qreal(y));
-    vector.setZ(qreal(z));
-    vector.setW(qreal(w));
+    vector.setX(x);
+    vector.setY(y);
+    vector.setZ(z);
+    vector.setW(w);
     return stream;
 }