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>

13 files changed, 247 insertions, 50 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;
 
diff --git a/src/datavisualization/engine/abstract3drenderer.cpp b/src/datavisualization/engine/abstract3drenderer.cpp
index 78f4b600..f031a34c 100644
--- a/src/datavisualization/engine/abstract3drenderer.cpp
+++ b/src/datavisualization/engine/abstract3drenderer.cpp
@@ -60,6 +60,7 @@ Abstract3DRenderer::Abstract3DRenderer(Abstract3DController *controller)
       m_visibleSeriesCount(0),
       m_customItemShader(0),
       m_volumeTextureShader(0),
+      m_volumeTextureLowDefShader(0),
       m_volumeTextureSliceShader(0),
       m_useOrthoProjection(false),
       m_xFlipped(false),
@@ -103,6 +104,7 @@ Abstract3DRenderer::~Abstract3DRenderer()
     delete m_selectionLabelItem;
     delete m_customItemShader;
     delete m_volumeTextureShader;
+    delete m_volumeTextureLowDefShader;
     delete m_volumeTextureSliceShader;
 
     foreach (SeriesRenderCache *cache, m_renderCacheList) {
@@ -198,22 +200,27 @@ void Abstract3DRenderer::initGradientShaders(const QString &vertexShader,
 void Abstract3DRenderer::initCustomItemShaders(const QString &vertexShader,
                                                const QString &fragmentShader)
 {
-    if (m_customItemShader)
-        delete m_customItemShader;
+    delete m_customItemShader;
     m_customItemShader = new ShaderHelper(this, vertexShader, fragmentShader);
     m_customItemShader->initialize();
 }
 
 void Abstract3DRenderer::initVolumeTextureShaders(const QString &vertexShader,
                                                   const QString &fragmentShader,
+                                                  const QString &fragmentLowDefShader,
                                                   const QString &sliceShader)
 {
-    if (m_volumeTextureShader)
-        delete m_volumeTextureShader;
+
+    delete m_volumeTextureShader;
     m_volumeTextureShader = new ShaderHelper(this, vertexShader, fragmentShader);
     m_volumeTextureShader->initialize();
-    if (m_volumeTextureSliceShader)
-        delete m_volumeTextureSliceShader;
+
+    delete m_volumeTextureLowDefShader;
+    m_volumeTextureLowDefShader = new ShaderHelper(this, vertexShader,
+                                                   fragmentLowDefShader);
+    m_volumeTextureLowDefShader->initialize();
+
+    delete m_volumeTextureSliceShader;
     m_volumeTextureSliceShader = new ShaderHelper(this, vertexShader, sliceShader);
     m_volumeTextureSliceShader->initialize();
 }
@@ -319,6 +326,7 @@ void Abstract3DRenderer::reInitShaders()
     }
     initVolumeTextureShaders(QStringLiteral(":/shaders/vertexTexture3D"),
                              QStringLiteral(":/shaders/fragmentTexture3D"),
+                             QStringLiteral(":/shaders/fragmentTexture3DLowDef"),
                              QStringLiteral(":/shaders/fragmentTexture3DSlice"));
 #else
     initGradientShaders(QStringLiteral(":/shaders/vertex"),
@@ -988,6 +996,7 @@ CustomRenderItem *Abstract3DRenderer::addCustomItem(QCustom3DItem *item)
         newItem->setSliceIndexZ(volumeItem->sliceIndexZ());
         newItem->setAlphaMultiplier(volumeItem->alphaMultiplier());
         newItem->setPreserveOpacity(volumeItem->preserveOpacity());
+        newItem->setUseHighDefShader(volumeItem->useHighDefShader());
 #endif
     }
     newItem->setScaling(scaling);
@@ -1068,15 +1077,15 @@ void Abstract3DRenderer::updateCustomItem(CustomRenderItem *renderItem)
             }
         } else
 #if !defined(QT_OPENGL_ES_2)
-         if (!item->d_ptr->m_isVolumeItem)
+            if (!item->d_ptr->m_isVolumeItem)
 #endif
-        {
-            renderItem->setBlendNeeded(textureImage.hasAlphaChannel());
-            GLuint oldTexture = renderItem->texture();
-            m_textureHelper->deleteTexture(&oldTexture);
-            GLuint texture = m_textureHelper->create2DTexture(textureImage, true, true, true);
-            renderItem->setTexture(texture);
-        }
+            {
+                renderItem->setBlendNeeded(textureImage.hasAlphaChannel());
+                GLuint oldTexture = renderItem->texture();
+                m_textureHelper->deleteTexture(&oldTexture);
+                GLuint texture = m_textureHelper->create2DTexture(textureImage, true, true, true);
+                renderItem->setTexture(texture);
+            }
         item->d_ptr->clearTextureImage();
         item->d_ptr->m_dirtyBits.textureDirty = false;
     }
@@ -1140,6 +1149,10 @@ void Abstract3DRenderer::updateCustomItem(CustomRenderItem *renderItem)
             renderItem->setPreserveOpacity(volumeItem->preserveOpacity());
             volumeItem->dptr()->m_dirtyBitsVolume.alphaDirty = false;
         }
+        if (volumeItem->dptr()->m_dirtyBitsVolume.shaderDirty) {
+            renderItem->setUseHighDefShader(volumeItem->useHighDefShader());
+            volumeItem->dptr()->m_dirtyBitsVolume.shaderDirty = false;
+        }
 #endif
     }
 }
@@ -1155,8 +1168,6 @@ void Abstract3DRenderer::updateCustomItemPositions()
 
 void Abstract3DRenderer::drawCustomItems(RenderingState state,
                                          ShaderHelper *regularShader,
-                                         ShaderHelper *volumeShader,
-                                         ShaderHelper *volumeSliceShader,
                                          const QMatrix4x4 &viewMatrix,
                                          const QMatrix4x4 &projectionViewMatrix,
                                          const QMatrix4x4 &depthProjectionViewMatrix,
@@ -1254,9 +1265,11 @@ void Abstract3DRenderer::drawCustomItems(RenderingState state,
                 if (item->sliceIndexX() >= 0
                         || item->sliceIndexY() >= 0
                         || item->sliceIndexZ() >= 0) {
-                    shader = volumeSliceShader;
+                    shader = m_volumeTextureSliceShader;
+                } else if (item->useHighDefShader()) {
+                    shader = m_volumeTextureShader;
                 } else {
-                    shader = volumeShader;
+                    shader = m_volumeTextureLowDefShader;
                 }
             } else {
                 shader = regularShader;
@@ -1309,7 +1322,7 @@ void Abstract3DRenderer::drawCustomItems(RenderingState state,
                     shader->setUniformValue(shader->alphaMultiplier(), item->alphaMultiplier());
                     shader->setUniformValue(shader->preserveOpacity(),
                                             item->preserveOpacity() ? 1 : 0);
-                    if (shader == volumeSliceShader) {
+                    if (shader == m_volumeTextureSliceShader) {
                         QVector3D slices((float(item->sliceIndexX()) + 0.5f)
                                          / float(item->textureWidth()) * 2.0 - 1.0,
                                          (float(item->sliceIndexY()) + 0.5f)
@@ -1323,11 +1336,21 @@ void Abstract3DRenderer::drawCustomItems(RenderingState state,
                         QVector3D textureDimensions(1.0f / float(item->textureWidth()),
                                                     1.0f / float(item->textureHeight()),
                                                     1.0f / float(item->textureDepth()));
-                        shader->setUniformValue(shader->textureDimensions(), textureDimensions);
 
                         // Worst case scenario sample count
-                        int sampleCount = item->textureWidth() + item->textureHeight()
-                                + item->textureDepth();
+                        int sampleCount;
+                        if (shader == m_volumeTextureLowDefShader) {
+                            sampleCount = qMax(item->textureWidth(),
+                                               qMax(item->textureDepth(), item->textureHeight()));
+                            // Further improve speed with big textures by simply dropping every
+                            // other sample:
+                            if (sampleCount > 256)
+                                sampleCount /= 2;
+                        } else {
+                            sampleCount = item->textureWidth() + item->textureHeight()
+                                    + item->textureDepth();
+                        }
+                        shader->setUniformValue(shader->textureDimensions(), textureDimensions);
                         shader->setUniformValue(shader->sampleCount(), sampleCount);
                     }
                     m_drawer->drawObject(shader, item->mesh(), 0, 0, item->texture());
diff --git a/src/datavisualization/engine/abstract3drenderer_p.h b/src/datavisualization/engine/abstract3drenderer_p.h
index 1e815463..83b4e1c7 100644
--- a/src/datavisualization/engine/abstract3drenderer_p.h
+++ b/src/datavisualization/engine/abstract3drenderer_p.h
@@ -94,6 +94,7 @@ public:
                                        const QString &fragmentShader);
     virtual void initVolumeTextureShaders(const QString &vertexShader,
                                           const QString &fragmentShader,
+                                          const QString &fragmentLowDefShader,
                                           const QString &sliceShader);
     virtual void updateAxisType(QAbstract3DAxis::AxisOrientation orientation,
                                 QAbstract3DAxis::AxisType type);
@@ -146,7 +147,6 @@ public:
     QString &selectionLabel();
 
     void drawCustomItems(RenderingState state, ShaderHelper *regularShader,
-                         ShaderHelper *volumeShader, ShaderHelper *volumeSliceShader,
                          const QMatrix4x4 &viewMatrix,
                          const QMatrix4x4 &projectionViewMatrix,
                          const QMatrix4x4 &depthProjectionViewMatrix,
@@ -243,6 +243,7 @@ protected:
 
     ShaderHelper *m_customItemShader;
     ShaderHelper *m_volumeTextureShader;
+    ShaderHelper *m_volumeTextureLowDefShader;
     ShaderHelper *m_volumeTextureSliceShader;
 
     bool m_useOrthoProjection;
diff --git a/src/datavisualization/engine/bars3drenderer.cpp b/src/datavisualization/engine/bars3drenderer.cpp
index 22bf6b87..1614b563 100644
--- a/src/datavisualization/engine/bars3drenderer.cpp
+++ b/src/datavisualization/engine/bars3drenderer.cpp
@@ -1090,8 +1090,7 @@ void Bars3DRenderer::drawScene(GLuint defaultFboHandle)
             }
         }
 
-        Abstract3DRenderer::drawCustomItems(RenderingDepth, m_depthShader, m_volumeTextureShader,
-                                            m_volumeTextureSliceShader, viewMatrix,
+        Abstract3DRenderer::drawCustomItems(RenderingDepth, m_depthShader, viewMatrix,
                                             projectionViewMatrix,
                                             depthProjectionViewMatrix, m_depthTexture,
                                             m_shadowQualityToShader);
@@ -1179,7 +1178,6 @@ void Bars3DRenderer::drawScene(GLuint defaultFboHandle)
         }
         glCullFace(GL_BACK);
         Abstract3DRenderer::drawCustomItems(RenderingSelection, m_selectionShader,
-                                            m_volumeTextureShader, m_volumeTextureSliceShader,
                                             viewMatrix,
                                             projectionViewMatrix, depthProjectionViewMatrix,
                                             m_depthTexture, m_shadowQualityToShader);
@@ -1234,7 +1232,6 @@ void Bars3DRenderer::drawScene(GLuint defaultFboHandle)
                        startBar, stopBar, stepBar, -1.0f);
 
         Abstract3DRenderer::drawCustomItems(RenderingNormal, m_customItemShader,
-                                            m_volumeTextureShader, m_volumeTextureSliceShader,
                                             viewMatrix, projectionViewMatrix,
                                             depthProjectionViewMatrix, m_depthTexture,
                                             m_shadowQualityToShader, -1.0f);
@@ -1272,8 +1269,7 @@ void Bars3DRenderer::drawScene(GLuint defaultFboHandle)
     drawGridLines(depthProjectionViewMatrix, projectionViewMatrix, viewMatrix);
 
     // Draw custom items
-    Abstract3DRenderer::drawCustomItems(RenderingNormal, m_customItemShader, m_volumeTextureShader,
-                                        m_volumeTextureSliceShader, viewMatrix,
+    Abstract3DRenderer::drawCustomItems(RenderingNormal, m_customItemShader, viewMatrix,
                                         projectionViewMatrix, depthProjectionViewMatrix,
                                         m_depthTexture, m_shadowQualityToShader);
 
diff --git a/src/datavisualization/engine/engine.qrc b/src/datavisualization/engine/engine.qrc
index 88440bec..0936bc16 100644
--- a/src/datavisualization/engine/engine.qrc
+++ b/src/datavisualization/engine/engine.qrc
@@ -64,5 +64,6 @@
         <file alias="fragmentTexture3DSlice">shaders/texture3dslice.frag</file>
         <file alias="vertexShadowNoMatrices">shaders/shadowNoMatrices.vert</file>
         <file alias="vertexNoMatrices">shaders/defaultNoMatrices.vert</file>
+        <file alias="fragmentTexture3DLowDef">shaders/texture3dlowdef.frag</file>
     </qresource>
 </RCC>
diff --git a/src/datavisualization/engine/scatter3drenderer.cpp b/src/datavisualization/engine/scatter3drenderer.cpp
index ca983dac..8c4644c6 100644
--- a/src/datavisualization/engine/scatter3drenderer.cpp
+++ b/src/datavisualization/engine/scatter3drenderer.cpp
@@ -575,8 +575,7 @@ void Scatter3DRenderer::drawScene(const GLuint defaultFboHandle)
             }
         }
 
-        Abstract3DRenderer::drawCustomItems(RenderingDepth, m_depthShader, m_volumeTextureShader,
-                                            m_volumeTextureSliceShader, viewMatrix,
+        Abstract3DRenderer::drawCustomItems(RenderingDepth, m_depthShader, viewMatrix,
                                             projectionViewMatrix,
                                             depthProjectionViewMatrix, m_depthTexture,
                                             m_shadowQualityToShader);
@@ -681,7 +680,6 @@ void Scatter3DRenderer::drawScene(const GLuint defaultFboHandle)
         }
 
         Abstract3DRenderer::drawCustomItems(RenderingSelection, m_selectionShader,
-                                            m_volumeTextureShader, m_volumeTextureSliceShader,
                                             viewMatrix, projectionViewMatrix,
                                             depthProjectionViewMatrix, m_depthTexture,
                                             m_shadowQualityToShader);
@@ -1455,8 +1453,7 @@ void Scatter3DRenderer::drawScene(const GLuint defaultFboHandle)
         }
     }
 
-    Abstract3DRenderer::drawCustomItems(RenderingNormal, m_customItemShader, m_volumeTextureShader,
-                                        m_volumeTextureSliceShader, viewMatrix,
+    Abstract3DRenderer::drawCustomItems(RenderingNormal, m_customItemShader, viewMatrix,
                                         projectionViewMatrix, depthProjectionViewMatrix,
                                         m_depthTexture, m_shadowQualityToShader);
 
diff --git a/src/datavisualization/engine/shaders/texture3d.frag b/src/datavisualization/engine/shaders/texture3d.frag
index 6dd7f78c..460cbcc6 100644
--- a/src/datavisualization/engine/shaders/texture3d.frag
+++ b/src/datavisualization/engine/shaders/texture3d.frag
@@ -74,9 +74,8 @@ void main() {
 
     highp vec4 destColor = vec4(0, 0, 0, 0);
     highp float totalOpacity = 1.0;
-    highp float nextOpacity = 1.0;
 
-    highp float extraAlphaMultiplier = fullDist * alphaThicknesses;
+    highp float extraAlphaMultiplier = fullDist * alphaThicknesses * alphaMultiplier;
 
     // nextEdges vector indicates the next edges of the texel boundaries along each axis that
     // the ray is about to cross. The first edges are offset by a fraction of a texel to
@@ -134,11 +133,10 @@ void main() {
         curLen += stepSize;
 
         if (curColor.a >= 0.0) {
-            curAlpha = alphaMultiplier * curColor.a;
-            if (curAlpha >= 1.0 || (curColor.a == 1.0 && preserveOpacity == 1))
+            if (curColor.a == 1.0 && (preserveOpacity == 1 || alphaMultiplier >= 1.0))
                 curAlpha = 1.0;
             else
-                curAlpha = curAlpha * extraAlphaMultiplier * stepSize;
+                curAlpha = curColor.a * extraAlphaMultiplier * stepSize;
             highp float nextOpacity = totalOpacity - curAlpha;
             // If opacity goes beyond full opacity, we need to adjust current alpha according
             // to the fraction of the distance the material is visible, so that we don't get
diff --git a/src/datavisualization/engine/shaders/texture3dlowdef.frag b/src/datavisualization/engine/shaders/texture3dlowdef.frag
new file mode 100644
index 00000000..72b959fc
--- /dev/null
+++ b/src/datavisualization/engine/shaders/texture3dlowdef.frag
@@ -0,0 +1,119 @@
+#version 120
+
+varying highp vec3 pos;
+
+uniform highp sampler3D textureSampler;
+uniform highp vec3 cameraPositionRelativeToModel;
+uniform highp vec4 colorIndex[256];
+uniform highp int color8Bit;
+uniform highp vec3 textureDimensions;
+uniform highp int sampleCount; // This is the maximum sample count
+uniform highp float alphaMultiplier;
+uniform highp int preserveOpacity;
+
+// Ray traveling straight through a single 'alpha thickness' applies 100% of the encountered alpha.
+// Rays traveling shorter distances apply a fraction. This is used to normalize the alpha over
+// entire volume, regardless of texture dimensions
+const highp float alphaThicknesses = 32.0;
+const highp float SQRT3 = 1.73205081;
+
+void main() {
+    highp vec3 rayDir = -(cameraPositionRelativeToModel - pos);
+    vec3 rayStart = pos;
+    // Flip Y and Z so QImage bits work directly for texture and first image is in the front
+    rayDir.yz = -rayDir.yz;
+    rayStart.yz = -rayStart.yz;
+
+    // Calculate ray intersection endpoint
+    vec3 rayStop;
+    if (rayDir.x == 0.0) {
+        rayStop.yz = rayStart.yz;
+        rayStop.x = -rayStart.x;
+    } else if (rayDir.y == 0.0) {
+        rayStop.xz = rayStart.xz;
+        rayStop.y = -rayStart.y;
+    } else if (rayDir.z == 0.0) {
+        rayStop.xy = rayStart.xy;
+        rayStop.z = -rayStart.z;
+    } else {
+        highp vec3 boxBounds = vec3(1.0, 1.0, 1.0);
+        highp vec3 invRayDir = 1.0 / rayDir;
+        if (rayDir.x < 0)
+            boxBounds.x = -1.0;
+        if (rayDir.y < 0)
+            boxBounds.y = -1.0;
+        if (rayDir.z < 0)
+            boxBounds.z = -1.0;
+        highp vec3 t = (boxBounds - rayStart) * invRayDir;
+        highp float minT = min(t.x, min(t.y, t.z));
+        rayStop = rayStart + minT * rayDir;
+    }
+
+    // Convert intersections to texture coords
+    rayStart = 0.5 * (rayStart + 1.0);
+    rayStop = 0.5 * (rayStop + 1.0);
+
+    highp vec3 ray = rayStop - rayStart;
+
+    // Avoid artifacts from divisions by zero
+    if (ray.x == 0)
+        ray.x = 0.000000001;
+    if (ray.y == 0)
+        ray.y = 0.000000001;
+    if (ray.z == 0)
+        ray.z = 0.000000001;
+
+
+    highp float fullDist = length(ray);
+    highp float stepSize = SQRT3 / sampleCount;
+    highp vec3 step = (SQRT3 * normalize(ray)) / sampleCount;
+
+    rayStart += (step * 0.001);
+
+    highp vec3 curPos = rayStart;
+    highp float curLen = 0.0;
+    highp vec4 curColor = vec4(0, 0, 0, 0);
+    highp float curAlpha = 0.0;
+    highp vec3 curRgb = vec3(0, 0, 0);
+    highp vec4 destColor = vec4(0, 0, 0, 0);
+    highp float totalOpacity = 1.0;
+
+    highp float extraAlphaMultiplier = stepSize * alphaThicknesses * alphaMultiplier;
+
+    // Raytrace into volume, need to sample pixels along the eye ray until we hit opacity 1
+    for (int i = 0; i < sampleCount; i++) {
+        curColor = texture3D(textureSampler, curPos);
+        if (color8Bit != 0)
+            curColor = colorIndex[int(curColor.r * 255.0)];
+
+        if (curColor.a >= 0.0) {
+            if (curColor.a == 1.0 && (preserveOpacity == 1 || alphaMultiplier >= 1.0))
+                curAlpha = 1.0;
+            else
+                curAlpha = curColor.a * extraAlphaMultiplier;
+            highp float nextOpacity = totalOpacity - curAlpha;
+            // If opacity goes beyond full opacity, we need to adjust current alpha according
+            // to the fraction of the distance the material is visible, so that we don't get
+            // box artifacts around texels.
+            if (nextOpacity < 0.0) {
+                curAlpha *= totalOpacity / curAlpha;
+                nextOpacity = 0.0;
+            }
+
+            curRgb = curColor.rgb * curAlpha * (totalOpacity + nextOpacity);
+            destColor.rgb += curRgb;
+            totalOpacity = nextOpacity;
+        }
+        curPos += step;
+        curLen += stepSize;
+        if (curLen >= fullDist || totalOpacity <= 0.0)
+            break;
+    }
+
+    // Brighten up the final color if there is some transparency left
+    if (totalOpacity >= 0.0 && totalOpacity < 1.0)
+        destColor *= (1.0 - (totalOpacity * 0.5)) / (1.0 - totalOpacity);
+
+    destColor.a = (1.0 - totalOpacity);
+    gl_FragColor = clamp(destColor, 0.0, 1.0);
+}
diff --git a/src/datavisualization/engine/surface3drenderer.cpp b/src/datavisualization/engine/surface3drenderer.cpp
index 58f97b0a..ced4c789 100644
--- a/src/datavisualization/engine/surface3drenderer.cpp
+++ b/src/datavisualization/engine/surface3drenderer.cpp
@@ -1196,8 +1196,7 @@ void Surface3DRenderer::drawScene(GLuint defaultFboHandle)
         glEnable(GL_CULL_FACE);
         glCullFace(GL_FRONT);
 
-        Abstract3DRenderer::drawCustomItems(RenderingDepth, m_depthShader, m_volumeTextureShader,
-                                            m_volumeTextureSliceShader, viewMatrix,
+        Abstract3DRenderer::drawCustomItems(RenderingDepth, m_depthShader, viewMatrix,
                                             projectionViewMatrix,
                                             depthProjectionViewMatrix, m_depthTexture,
                                             m_shadowQualityToShader);
@@ -1234,8 +1233,7 @@ void Surface3DRenderer::drawScene(GLuint defaultFboHandle)
 
         glDisableVertexAttribArray(m_depthShader->posAtt());
 
-        Abstract3DRenderer::drawCustomItems(RenderingDepth, m_depthShader, m_volumeTextureShader,
-                                            m_volumeTextureSliceShader, viewMatrix,
+        Abstract3DRenderer::drawCustomItems(RenderingDepth, m_depthShader, viewMatrix,
                                             projectionViewMatrix,
                                             depthProjectionViewMatrix, m_depthTexture,
                                             m_shadowQualityToShader);
@@ -1292,7 +1290,6 @@ void Surface3DRenderer::drawScene(GLuint defaultFboHandle)
         }
         m_surfaceGridShader->bind();
         Abstract3DRenderer::drawCustomItems(RenderingSelection, m_surfaceGridShader,
-                                            m_volumeTextureShader, m_volumeTextureSliceShader,
                                             viewMatrix,
                                             projectionViewMatrix, depthProjectionViewMatrix,
                                             m_depthTexture, m_shadowQualityToShader);
@@ -1864,8 +1861,7 @@ void Surface3DRenderer::drawScene(GLuint defaultFboHandle)
         }
     }
 
-    Abstract3DRenderer::drawCustomItems(RenderingNormal, m_customItemShader, m_volumeTextureShader,
-                                        m_volumeTextureSliceShader, viewMatrix,
+    Abstract3DRenderer::drawCustomItems(RenderingNormal, m_customItemShader, viewMatrix,
                                         projectionViewMatrix, depthProjectionViewMatrix,
                                         m_depthTexture, m_shadowQualityToShader);