From dd5c97a077ef70990e89da0a4b679c4f4b35d108 Mon Sep 17 00:00:00 2001
From: Uwe Rathmann <Uwe.Rathmann@tigertal.de>
Date: Tue, 6 May 2025 10:59:15 +0200
Subject: [PATCH] QskGradientStop interpolation formalized

---
 src/common/QskGradientStop.cpp      | 56 ++++++++++++++++-------------
 src/common/QskGradientStop.h        |  6 ++--
 src/common/QskTextColors.h          |  2 +-
 src/controls/QskVariantAnimator.cpp |  2 ++
 4 files changed, 39 insertions(+), 27 deletions(-)

diff --git a/src/common/QskGradientStop.cpp b/src/common/QskGradientStop.cpp
index 50ffdad6..f0d37ff7 100644
--- a/src/common/QskGradientStop.cpp
+++ b/src/common/QskGradientStop.cpp
@@ -56,26 +56,19 @@ QskHashValue QskGradientStop::hash( QskHashValue seed ) const noexcept
     return qHashBits( &m_color, sizeof( m_color ), hash );
 }
 
-QColor QskGradientStop::interpolated(
-    const QskGradientStop& s1, const QskGradientStop& s2, qreal position ) noexcept
+QskGradientStop QskGradientStop::interpolated(
+    const QskGradientStop& to, qreal ratio ) const
 {
-    if ( s1.color() == s2.color() )
-        return s1.color();
+    return QskGradientStop(
+        m_position + ( to.m_position - m_position ) * ratio,
+        QskRgb::interpolated( m_color, to.m_color, ratio )
+    );
+}
 
-    auto min = &s1;
-    auto max = &s2;
-
-    if ( min->position() > max->position() )
-        std::swap( min, max );
-
-    if ( position <= min->position() )
-        return min->color();
-
-    if ( position >= max->position() )
-        return max->color();
-
-    const qreal r = ( position - min->position() ) / ( max->position() - min->position() );
-    return QskRgb::interpolated( min->color(), max->color(), r );
+QVariant QskGradientStop::interpolate(
+    const QskGradientStop& from, const QskGradientStop& to, qreal ratio )
+{
+    return QVariant::fromValue( from.interpolated( to, ratio ) );
 }
 
 #ifndef QT_NO_DEBUG_STREAM
@@ -95,19 +88,32 @@ QDebug operator<<( QDebug debug, const QskGradientStop& stop )
 
 #endif
 
-#include "moc_QskGradientStop.cpp"
-
 // some helper functions around QskGradientStops
 
 static inline QColor qskInterpolatedColor(
     const QskGradientStops& stops, int index1, int index2, qreal position )
 {
-    const auto max = static_cast< int >( stops.count() ) - 1;
+    {
+        const auto max = static_cast< int >( stops.count() ) - 1;
 
-    index1 = qBound( 0, index1, max );
-    index2 = qBound( 0, index2, max );
+        index1 = qBound( 0, index1, max );
+        index2 = qBound( 0, index2, max );
+    }
 
-    return QskGradientStop::interpolated( stops[ index1 ], stops[ index2 ], position );
+    const auto& s1 = stops[ index1 ];
+    const auto& s2 = stops[ index2 ];
+
+    if ( s1.color() == s2.color() )
+        return s1.color();
+
+    if ( position <= s1.position() )
+        return s1.color();
+
+    if ( position >= s2.position() )
+        return s2.color();
+
+    const qreal r = ( position - s1.position() ) / ( s2.position() - s1.position() );
+    return QskRgb::interpolated( s1.color(), s2.color(), r );
 }
 
 bool qskIsVisible( const QskGradientStops& stops ) noexcept
@@ -463,3 +469,5 @@ QGradientStops qskToQGradientStops( const QskGradientStops& stops )
 
     return qStops;
 }
+
+#include "moc_QskGradientStop.cpp"
diff --git a/src/common/QskGradientStop.h b/src/common/QskGradientStop.h
index b8e841f3..fbad2ea0 100644
--- a/src/common/QskGradientStop.h
+++ b/src/common/QskGradientStop.h
@@ -45,8 +45,10 @@ class QSK_EXPORT QskGradientStop
     void setRgb( QRgb ) noexcept;
     QRgb rgb() const noexcept;
 
-    static QColor interpolated(
-        const QskGradientStop&, const QskGradientStop&, qreal position ) noexcept;
+    QskGradientStop interpolated( const QskGradientStop&, qreal ) const;
+
+    static QVariant interpolate( const QskGradientStop&,
+        const QskGradientStop&, qreal );
 
     QskHashValue hash( QskHashValue seed ) const noexcept;
 
diff --git a/src/common/QskTextColors.h b/src/common/QskTextColors.h
index b01b5c46..1cf13d27 100644
--- a/src/common/QskTextColors.h
+++ b/src/common/QskTextColors.h
@@ -41,7 +41,7 @@ class QSK_EXPORT QskTextColors
     void setLinkColor( QRgb );
     void setLinkColor( Qt::GlobalColor );
 
-    QskTextColors interpolated( const QskTextColors&, qreal value ) const;
+    QskTextColors interpolated( const QskTextColors&, qreal ratio ) const;
 
     static QVariant interpolate( const QskTextColors&,
         const QskTextColors&, qreal ratio );
diff --git a/src/controls/QskVariantAnimator.cpp b/src/controls/QskVariantAnimator.cpp
index 631fae2f..45431e09 100644
--- a/src/controls/QskVariantAnimator.cpp
+++ b/src/controls/QskVariantAnimator.cpp
@@ -13,6 +13,7 @@
 #include "QskGraduationMetrics.h"
 #include "QskColorFilter.h"
 #include "QskGradient.h"
+#include "QskGradientStop.h"
 #include "QskMargins.h"
 #include "QskIntervalF.h"
 #include "QskTextColors.h"
@@ -43,6 +44,7 @@ static void qskRegisterInterpolator()
     qRegisterAnimationInterpolator< QskColorFilter >( QskColorFilter::interpolate );
     qRegisterAnimationInterpolator< QskIntervalF >( QskIntervalF::interpolate );
     qRegisterAnimationInterpolator< QskMargins >( QskMargins::interpolate );
+    qRegisterAnimationInterpolator< QskGradientStop >( QskGradientStop::interpolate );
     qRegisterAnimationInterpolator< QskGradient >( QskGradient::interpolate );
     qRegisterAnimationInterpolator< QskBoxShapeMetrics >( QskBoxShapeMetrics::interpolate );
     qRegisterAnimationInterpolator< QskBoxBorderMetrics >( QskBoxBorderMetrics::interpolate );