caching some values for faster valueAt calculations

src/common/QskGradientDirection.cpp

@@ -40,6 +40,7 @@ void QskLinearDirection::setVector( const QLineF& vector ) noexcept
     m_y1 = vector.y1();
     m_x2 = vector.x2();
     m_y2 = vector.y2();
+    m_dot = -1.0;
 }
 
 void QskLinearDirection::setVector( const QPointF& start, const QPointF& stop ) noexcept
@@ -48,6 +49,7 @@ void QskLinearDirection::setVector( const QPointF& start, const QPointF& stop )
     m_y1 = start.y();
     m_x2 = stop.x();
     m_y2 = stop.y();
+    m_dot = -1.0;
 }
 
 void QskLinearDirection::setVector( qreal x1, qreal y1, qreal x2, qreal y2 ) noexcept
@@ -56,50 +58,59 @@ void QskLinearDirection::setVector( qreal x1, qreal y1, qreal x2, qreal y2 ) noe
     m_y1 = y1;
     m_x2 = x2;
     m_y2 = y2;
+    m_dot = -1.0;
 }
 
 void QskLinearDirection::setStart( const QPointF& pos ) noexcept
 {
     m_x1 = pos.x();
     m_y1 = pos.y();
+    m_dot = -1.0;
 }
 
 void QskLinearDirection::setStart( qreal x, qreal y ) noexcept
 {
     m_x1 = x;
     m_y1 = y;
+    m_dot = -1.0;
 }
 
 void QskLinearDirection::setStop( const QPointF& pos ) noexcept
 {
     m_x2 = pos.x();
     m_y2 = pos.y();
+    m_dot = -1.0;
 }
 
 void QskLinearDirection::setStop( qreal x, qreal y ) noexcept
 {
     m_x2 = x;
     m_y2 = y;
+    m_dot = -1.0;
 }
 
 void QskLinearDirection::setX1( qreal x ) noexcept
 {
     m_x1 = x;
+    m_dot = -1.0;
 }
 
 void QskLinearDirection::setY1( qreal y ) noexcept
 {
     m_y1 = y;
+    m_dot = -1.0;
 }
 
 void QskLinearDirection::setX2( qreal x ) noexcept
 {
     m_x2 = x;
+    m_dot = -1.0;
 }
 
 void QskLinearDirection::setY2( qreal y ) noexcept
 {
     m_y2 = y;
+    m_dot = -1.0;
 }
 
 void QskLinearDirection::setInterval( Qt::Orientation orientation, qreal from, qreal to )
@@ -114,6 +125,14 @@ void QskLinearDirection::setInterval( Qt::Orientation orientation, qreal from, q
         m_x1 = from;
         m_x2 = to;
     }
+    m_dot = -1.0;
+}
+
+void QskLinearDirection::precalculate() const noexcept
+{
+    m_dx = m_x2 - m_x1;
+    m_dy = m_y2 - m_y1; 
+    m_dot = m_dx * m_dx + m_dy * m_dy;
 }
 
 static inline bool qskIntersectsTop(
@@ -133,14 +152,14 @@ static inline bool qskIntersectsBottom(
 static inline bool qskIntersectsLeft(
     qreal vx, qreal vy, qreal m, const QRectF& rect )
 {
-    const qreal cy = vy - ( vx - rect.left() ) * m;
+    const auto cy = vy - ( vx - rect.left() ) * m;
     return ( cy > rect.top() && cy < rect.bottom() );
 }
 
 static inline bool qskIntersectsRight(
     qreal vx, qreal vy, qreal m, const QRectF& rect )
 {
-    const qreal cy = vy - ( vx - rect.right() ) * m;
+    const auto cy = vy - ( vx - rect.right() ) * m;
     return ( cy > rect.top() && cy < rect.bottom() );
 }
 
@@ -152,7 +171,6 @@ bool QskLinearDirection::contains( const QRectF& rect ) const
             || ( m_x1 >= rect.right() && m_x2 <= rect.left() );
     }
 
-
     if ( m_x1 == m_x2 )
     {
         return ( m_y1 <= rect.top() && m_y2 >= rect.bottom() )

src/common/QskGradientDirection.h

@@ -68,6 +68,9 @@ class QSK_EXPORT QskLinearDirection
     constexpr qreal y2() const noexcept;
     void setY2( qreal ) noexcept;
 
+    qreal dx() const noexcept;
+    qreal dy() const noexcept;
+
     /*
         In direction of the gradient vector, where 0.0 corresponds to
         points on the perpendicular at the start and 1.0 to points on
@@ -82,10 +85,16 @@ class QSK_EXPORT QskLinearDirection
     bool contains( const QRectF& ) const;
 
   private:
+    void precalculate() const noexcept;
+
     qreal m_x1 = 0.0;
     qreal m_y1 = 0.0;
     qreal m_x2 = 0.0;
     qreal m_y2 = 1.0;
+
+    mutable qreal m_dx = 0.0;
+    mutable qreal m_dy = 0.0;
+    mutable qreal m_dot = -1.0;
 };
 
 class QSK_EXPORT QskConicDirection
@@ -219,6 +228,22 @@ inline constexpr qreal QskLinearDirection::y2() const noexcept
     return m_y2;
 }
 
+inline qreal QskLinearDirection::dx() const noexcept
+{
+    if ( m_dot < 0.0 )
+        precalculate();
+
+    return m_dx;
+}
+
+inline qreal QskLinearDirection::dy() const noexcept
+{
+    if ( m_dot < 0.0 )
+        precalculate();
+
+    return m_dy;
+}
+
 inline constexpr QLineF QskLinearDirection::vector() const noexcept
 {
     return QLineF( m_x1, m_y1, m_x2, m_y2 );
@@ -262,12 +287,10 @@ inline qreal QskLinearDirection::valueAt( const QPointF& pos ) const
 
 inline qreal QskLinearDirection::valueAt( qreal x, qreal y ) const
 {
-    // we could cache these values TODO ..
+    if ( m_dot < 0.0 )
-    const qreal dx = m_x2 - m_x1;
+        precalculate();
-    const qreal dy = m_y2 - m_y1;
-    const qreal dot = dx * dx + dy * dy;
 
-    return ( ( x - m_x1 ) * dx + ( y - m_y1 ) * dy ) / dot;
+    return ( ( x - m_x1 ) * m_dx + ( y - m_y1 ) * m_dy ) / m_dot;
 }
 
 inline constexpr QskConicDirection::QskConicDirection(