Add option to use low definition volume shader.

Low definition volume shader samples the texture at even
intervals, so it will sometimes skip texels, causing flickering.

Change-Id: Iee6cb0e8893498b89ce1a40f34701a53d100283e
Reviewed-by: Tomi Korpipää <tomi.korpipaa@digia.com>

5 files changed, 70 insertions, 4 deletions

diff --git a/src/datavisualization/data/customrenderitem.cpp b/src/datavisualization/data/customrenderitem.cpp
index c316fd38..555f48b7 100644
--- a/src/datavisualization/data/customrenderitem.cpp
+++ b/src/datavisualization/data/customrenderitem.cpp
@@ -42,7 +42,8 @@ CustomRenderItem::CustomRenderItem()
       m_sliceIndexY(-1),
       m_sliceIndexZ(-1),
       m_alphaMultiplier(1.0f),
-      m_preserveOpacity(true)
+      m_preserveOpacity(true),
+      m_useHighDefShader(true)
 {
 }
 
diff --git a/src/datavisualization/data/customrenderitem_p.h b/src/datavisualization/data/customrenderitem_p.h
index 5428ce43..5024270a 100644
--- a/src/datavisualization/data/customrenderitem_p.h
+++ b/src/datavisualization/data/customrenderitem_p.h
@@ -96,6 +96,8 @@ public:
     inline float alphaMultiplier() const { return m_alphaMultiplier; }
     inline void setPreserveOpacity(bool enable) { m_preserveOpacity = enable; }
     inline bool preserveOpacity() const { return m_preserveOpacity; }
+    inline void setUseHighDefShader(bool enable) { m_useHighDefShader = enable; }
+    inline bool useHighDefShader() const {return m_useHighDefShader; }
 
 private:
     Q_DISABLE_COPY(CustomRenderItem)
@@ -126,6 +128,7 @@ private:
     int m_sliceIndexZ;
     float m_alphaMultiplier;
     bool m_preserveOpacity;
+    bool m_useHighDefShader;
 };
 typedef QHash<QCustom3DItem *, CustomRenderItem *> CustomRenderItemArray;
 
diff --git a/src/datavisualization/data/qcustom3dvolume.cpp b/src/datavisualization/data/qcustom3dvolume.cpp
index 503d324d..789b7718 100644
--- a/src/datavisualization/data/qcustom3dvolume.cpp
+++ b/src/datavisualization/data/qcustom3dvolume.cpp
@@ -136,6 +136,24 @@ QT_BEGIN_NAMESPACE_DATAVISUALIZATION
  */
 
 /*!
+ * \qmlproperty bool Custom3DVolume::useHighDefShader
+ *
+ * If this property value is \c{true}, a high definition shader is used to render the volume.
+ * If it is \c{false}, a low definition shader is used.
+ *
+ * The high definition shader guarantees that every visible texel of the volume texture is sampled
+ * when the volume is rendered.
+ * The low definition shader renders only a rough approximation of the volume contents,
+ * but at much higher frame rate. The low definition shader doesn't guarantee every texel of the
+ * volume texture is sampled, so there may be flickering if the volume contains distinct thin
+ * features.
+ *
+ * \note This value doesn't affect the level of detail when rendering the slices of the volume.
+ *
+ * Defaults to \c{true}.
+ */
+
+/*!
  * Constructs QCustom3DVolume with given \a parent.
  */
 QCustom3DVolume::QCustom3DVolume(QObject *parent) :
@@ -673,6 +691,40 @@ bool QCustom3DVolume::preserveOpacity() const
 }
 
 /*!
+ * \property QCustom3DVolume::useHighDefShader
+ *
+ * If this property value is \c{true}, a high definition shader is used to render the volume.
+ * If it is \c{false}, a low definition shader is used.
+ *
+ * The high definition shader guarantees that every visible texel of the volume texture is sampled
+ * when the volume is rendered.
+ * The low definition shader renders only a rough approximation of the volume contents,
+ * but at much higher frame rate. The low definition shader doesn't guarantee every texel of the
+ * volume texture is sampled, so there may be flickering if the volume contains distinct thin
+ * features.
+ *
+ * \note This value doesn't affect the level of detail when rendering the slices of the volume.
+ *
+ * Defaults to \c{true}.
+ *
+ * \sa renderSlice()
+ */
+void QCustom3DVolume::setUseHighDefShader(bool enable)
+{
+    if (dptr()->m_useHighDefShader != enable) {
+        dptr()->m_useHighDefShader = enable;
+        dptr()->m_dirtyBitsVolume.shaderDirty = true;
+        emit useHighDefShaderChanged(enable);
+        emit dptr()->needUpdate();
+    }
+}
+
+bool QCustom3DVolume::useHighDefShader() const
+{
+    return dptrc()->m_useHighDefShader;
+}
+
+/*!
  * Renders the slice specified by \a index along \a axis into an image.
  * The texture format of this object is used.
  *
@@ -712,7 +764,8 @@ QCustom3DVolumePrivate::QCustom3DVolumePrivate(QCustom3DVolume *q) :
     m_textureFormat(QImage::Format_ARGB32),
     m_textureData(0),
     m_alphaMultiplier(1.0f),
-    m_preserveOpacity(true)
+    m_preserveOpacity(true),
+    m_useHighDefShader(true)
 {
     m_isVolumeItem = true;
     m_meshFile = QStringLiteral(":/defaultMeshes/barFull");
@@ -736,7 +789,8 @@ QCustom3DVolumePrivate::QCustom3DVolumePrivate(QCustom3DVolume *q, const QVector
     m_colorTable(colorTable),
     m_textureData(textureData),
     m_alphaMultiplier(1.0f),
-    m_preserveOpacity(true)
+    m_preserveOpacity(true),
+    m_useHighDefShader(true)
 {
     m_isVolumeItem = true;
     m_shadowCasting = false;
diff --git a/src/datavisualization/data/qcustom3dvolume.h b/src/datavisualization/data/qcustom3dvolume.h
index 8627eb71..23ae07d9 100644
--- a/src/datavisualization/data/qcustom3dvolume.h
+++ b/src/datavisualization/data/qcustom3dvolume.h
@@ -41,6 +41,7 @@ class QT_DATAVISUALIZATION_EXPORT QCustom3DVolume : public QCustom3DItem
     Q_PROPERTY(QVector<uchar> *textureData READ textureData WRITE setTextureData NOTIFY textureDataChanged)
     Q_PROPERTY(float alphaMultiplier READ alphaMultiplier WRITE setAlphaMultiplier NOTIFY alphaMultiplierChanged)
     Q_PROPERTY(bool preserveOpacity READ preserveOpacity WRITE setPreserveOpacity NOTIFY preserveOpacityChanged)
+    Q_PROPERTY(bool useHighDefShader READ useHighDefShader WRITE setUseHighDefShader NOTIFY useHighDefShaderChanged)
 
 public:
 
@@ -86,6 +87,9 @@ public:
     void setPreserveOpacity(bool enable);
     bool preserveOpacity() const;
 
+    void setUseHighDefShader(bool enable);
+    bool useHighDefShader() const;
+
     QImage renderSlice(Qt::Axis axis, int index);
 
 signals:
@@ -100,6 +104,7 @@ signals:
     void textureFormatChanged(QImage::Format format);
     void alphaMultiplierChanged(float mult);
     void preserveOpacityChanged(bool enabled);
+    void useHighDefShaderChanged(bool enabled);
 
 protected:
     QCustom3DVolumePrivate *dptr();
diff --git a/src/datavisualization/data/qcustom3dvolume_p.h b/src/datavisualization/data/qcustom3dvolume_p.h
index b83e27fb..8b0b439e 100644
--- a/src/datavisualization/data/qcustom3dvolume_p.h
+++ b/src/datavisualization/data/qcustom3dvolume_p.h
@@ -41,6 +41,7 @@ struct QCustomVolumeDirtyBitField {
     bool textureDataDirty       : 1;
     bool textureFormatDirty     : 1;
     bool alphaDirty             : 1;
+    bool shaderDirty            : 1;
 
     QCustomVolumeDirtyBitField()
         : textureDimensionsDirty(false),
@@ -48,7 +49,8 @@ struct QCustomVolumeDirtyBitField {
           colorTableDirty(false),
           textureDataDirty(false),
           textureFormatDirty(false),
-          alphaDirty(false)
+          alphaDirty(false),
+          shaderDirty(false)
     {
     }
 };
@@ -84,6 +86,7 @@ public:
 
     float m_alphaMultiplier;
     bool m_preserveOpacity;
+    bool m_useHighDefShader;
 
     QCustomVolumeDirtyBitField m_dirtyBitsVolume;