Started work on implementing a particle field flow visualization:

* Introducing ParticleFlowRenderer processor implementing a particle simulation using OpenGL transform feedback
* Added tgt::Shader::selectSubroutine()
* Added tgt::VertexArrayObject::getId()

ext/tgt/shadermanager.cpp

@@ -1322,6 +1322,16 @@ void Shader::setNormalizedAttribute(GLint index, const Vector4<GLuint>& v) {
     glVertexAttrib4Nuiv(index, v.elem);
 }
 
+bool Shader::selectSubroutine(ShaderObject::ShaderType type, const std::string& subroutineName) {
+    GLuint index = glGetSubroutineIndex(id_, type, subroutineName.c_str());
+    if (index == -1) {
+        LWARNING("Failed to locate subroutine Location: " << subroutineName);
+        return false;
+    }
+    glUniformSubroutinesuiv(type, 1, &index);
+    return true;
+}
+
 //------------------------------------------------------------------------------
 
 const string ShaderManager::loggerCat_("tgt.Shader.Manager");

ext/tgt/shadermanager.h

@@ -258,6 +258,10 @@ public:
 
     std::string getLinkerLog() const;
 
+    // Subroutines
+    bool selectSubroutine(ShaderObject::ShaderType type, const std::string& subroutineName);
+
+
     //
     // Uniform stuff
     //

ext/tgt/vertexarrayobject.cpp

@@ -80,4 +80,8 @@ namespace tgt {
             tgtAssert(false, "Could not find Vertex Attribute location for this BufferObject. You have to add it first using setVertexAttributePointer()!");
     }
 
+    GLuint VertexArrayObject::getId() const {
+        return _id;
+    }
+
 }
\ No newline at end of file

ext/tgt/vertexarrayobject.h

@@ -30,6 +30,12 @@ namespace tgt {
          */
         ~VertexArrayObject();
 
+        /**
+         * Returns the OpneGL object ID
+         * \return  _id
+         */
+        GLuint getId() const;
+
         /**
          * Binds this VertexArrayObject to the current OpenGL context.
          */

modules/vectorfield/glsl/particleflowrenderer.frag

+// ================================================================================================
+// 
+// This file is part of the CAMPVis Software Framework.
+// 
+// If not explicitly stated otherwise: Copyright (C) 2012-2014, all rights reserved,
+//      Christian Schulte zu Berge <christian.szb@in.tum.de>
+//      Chair for Computer Aided Medical Procedures
+//      Technische Universitaet Muenchen
+//      Boltzmannstr. 3, 85748 Garching b. Muenchen, Germany
+// 
+// For a full list of authors and contributors, please refer to the file "AUTHORS.txt".
+// 
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file 
+// except in compliance with the License. You may obtain a copy of the License at
+// 
+// http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software distributed under the 
+// License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, 
+// either express or implied. See the License for the specific language governing permissions 
+// and limitations under the License.
+// 
+// ================================================================================================
+
+#include "tools/shading.frag"
+
+in float ex_Transparency;
+
+out vec4 out_Color; ///< outgoing fragment color
+
+void main() {
+    out_Color = vec4(1.0, 0.5, 0.0, 1.0) * ex_Transparency;
+
+
+#ifdef ENABLE_SHADING___
+    // compute gradient (needed for shading and normals)
+    vec3 gradient = ex_Normal;
+    out_Color.rgb = calculatePhongShading(ex_Position, _lightSource, _cameraPosition, gradient, _color.rgb, _color.rgb, vec3(1.0, 1.0, 1.0));
+#endif
+
+}

modules/vectorfield/glsl/particleflowrenderer.vert

+// ================================================================================================
+// 
+// This file is part of the CAMPVis Software Framework.
+// 
+// If not explicitly stated otherwise: Copyright (C) 2012-2014, all rights reserved,
+//      Christian Schulte zu Berge <christian.szb@in.tum.de>
+//      Chair for Computer Aided Medical Procedures
+//      Technische Universitaet Muenchen
+//      Boltzmannstr. 3, 85748 Garching b. Muenchen, Germany
+// 
+// For a full list of authors and contributors, please refer to the file "AUTHORS.txt".
+// 
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file 
+// except in compliance with the License. You may obtain a copy of the License at
+// 
+// http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software distributed under the 
+// License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, 
+// either express or implied. See the License for the specific language governing permissions 
+// and limitations under the License.
+// 
+// ================================================================================================
+
+#include "tools/texture3d.frag"
+
+subroutine void RenderPassType();
+subroutine uniform RenderPassType RenderPass;
+
+layout(location = 0) in vec3 in_Position;
+layout(location = 1) in vec3 in_Velocity;
+layout(location = 2) in float in_StartTime;
+layout(location = 3) in vec3 in_InitialPosition;
+
+out vec3 ex_Position;
+out vec3 ex_Velocity;
+out float ex_StartTime;
+
+out float ex_Transparency;
+
+/// Matrix defining model-to-world transformation
+uniform mat4 _modelMatrix = mat4(
+    1.0, 0.0, 0.0, 0.0,
+    0.0, 1.0, 0.0, 0.0,
+    0.0, 0.0, 1.0, 0.0,
+    0.0, 0.0, 0.0, 1.0);
+
+/// Matrix defining view transformation
+uniform mat4 _viewMatrix = mat4(
+    1.0, 0.0, 0.0, 0.0,
+    0.0, 1.0, 0.0, 0.0,
+    0.0, 0.0, 1.0, 0.0,
+    0.0, 0.0, 0.0, 1.0);
+
+/// Matrix defining projection transformation
+uniform mat4 _projectionMatrix = mat4(
+    1.0, 0.0, 0.0, 0.0,
+    0.0, 1.0, 0.0, 0.0,
+    0.0, 0.0, 1.0, 0.0,
+    0.0, 0.0, 0.0, 1.0);
+
+
+uniform float _time;
+uniform float _frameLength;
+uniform float _lifetime;
+
+uniform sampler3D _volume;
+uniform TextureParameters3D _volumeTextureParams;
+
+
+subroutine (RenderPassType)
+void update() {
+    if (_time > in_StartTime) {
+        float age = in_StartTime - _time;
+        if (age > _lifetime) {
+            // particle expired, recycle
+            ex_Position = in_InitialPosition;
+            ex_Velocity = texture(_volume, (_volumeTextureParams._worldToTextureMatrix * vec4(ex_Position, 1.0)).xyz).xyz;
+            ex_StartTime = _time;
+        }
+        else {
+            // particle alive, advance
+            ex_Position = in_Position + (in_Velocity * _frameLength * 0.1);
+
+            // compute new velocity by mixture of old velocity and flow at current location, model some inertia
+            vec3 v = texture(_volume, (_volumeTextureParams._worldToTextureMatrix * vec4(ex_Position, 1.0)).xyz).xyz;
+            ex_Velocity = mix(in_Velocity, v, 0.5);//smoothstep(0.5, 2.0, v/in_Velocity));
+            ex_StartTime = in_StartTime;
+        }
+    }
+    else {
+        ex_Position = in_Position;
+        ex_Velocity = in_Velocity;
+        ex_StartTime = in_StartTime;
+    }
+}
+
+
+subroutine (RenderPassType)
+void render() {
+    float age = _time - in_StartTime;
+    ex_Transparency = 1.0;// - (age / _lifetime);
+
+    gl_Position = _projectionMatrix * (_viewMatrix * (_modelMatrix * vec4(in_Position, 1.0)));
+    //ex_Position = in_Position;
+    mat4 normalMatrix = transpose(inverse(_modelMatrix));
+
+    //vec4 normalTmp = (normalMatrix * vec4(in_Normal, 0.0));
+    // ex_Normal = normalize((normalTmp).xyz);
+}
+
+void main() {
+    // call the current subroutine
+    RenderPass();
+}

modules/vectorfield/pipelines/vectorfielddemo.cpp

@@ -36,6 +36,7 @@ namespace campvis {
         , _lsp()
         , _imageReader()
         , _vectorFieldReader()
+        , _pfr(&_canvasSize)
         , _vectorFieldRenderer(&_canvasSize)
         , _sliceRenderer(&_canvasSize)
         , _rtc(&_canvasSize)
@@ -53,6 +54,7 @@ namespace campvis {
         addProcessor(&_lsp);
         addProcessor(&_imageReader);
         addProcessor(&_vectorFieldReader);
+        addProcessor(&_pfr);
         addProcessor(&_vectorFieldRenderer);
         addProcessor(&_sliceRenderer);
         addProcessor(&_rtc);
@@ -65,6 +67,7 @@ namespace campvis {
         AutoEvaluationPipeline::init();
 
         p_camera.addSharedProperty(&_vectorFieldRenderer.p_camera);
+        p_camera.addSharedProperty(&_pfr.p_camera);
         p_camera.addSharedProperty(&_sliceRenderer.p_camera);
 
         p_sliceNumber.addSharedProperty(&_vectorFieldRenderer.p_sliceNumber);
@@ -78,6 +81,7 @@ namespace campvis {
 
         _vectorFieldReader.p_url.setValue(CAMPVIS_SOURCE_DIR "/modules/vectorfield/sampledata/result_vec.mhd");
         _vectorFieldReader.p_targetImageID.setValue("vectors");
+        _vectorFieldReader.p_targetImageID.addSharedProperty(&_pfr.p_inputVectors);
         _vectorFieldReader.p_targetImageID.addSharedProperty(&_vectorFieldRenderer.p_inputVectors);
 
         _vectorFieldRenderer.p_renderOutput.addSharedProperty(&_rtc.p_firstImageId);
@@ -90,12 +94,21 @@ namespace campvis {
         _vectorFieldRenderer.p_lenThresholdMax.setValue(400.f);
         _vectorFieldRenderer.p_sliceOrientation.setValue(3);
 
+        _pfr.p_lenThresholdMin.setValue(100.f);
+        _pfr.p_flowProfile1.setValue(0.4716088614374652f);
+        _pfr.p_flowProfile2.setValue(0.0638348311845516f);
+        _pfr.p_flowProfile3.setValue(0.1713471562960614f);
+        _pfr.p_flowProfile4.setValue(0.1019371804834016f);
+        _pfr.p_lenThresholdMax.setValue(400.f);
+        _pfr.p_renderOutput.setValue("particles");
+
         Geometry1DTransferFunction* tf = new Geometry1DTransferFunction(128, tgt::vec2(0.f, 1.f));
         tf->addGeometry(TFGeometry1D::createQuad(tgt::vec2(0.f, 1.f), tgt::col4(0, 0, 0, 255), tgt::col4(255, 255, 255, 255)));
         _sliceRenderer.p_transferFunction.replaceTF(tf);
         _sliceRenderer.p_targetImageID.setValue("slice");
-        _sliceRenderer.p_targetImageID.addSharedProperty(&_rtc.p_secondImageId);
+        //_sliceRenderer.p_targetImageID.addSharedProperty(&_rtc.p_secondImageId);
 
+        _rtc.p_secondImageId.setValue("particles");
         _rtc.p_compositingMethod.selectById("depth");
         _rtc.p_targetImageId.setValue("composed");
 

modules/vectorfield/pipelines/vectorfielddemo.h

@@ -32,6 +32,7 @@
 
 #include "modules/base/processors/lightsourceprovider.h"
 #include "modules/io/processors/mhdimagereader.h"
+#include "modules/vectorfield/processors/particleflowrenderer.h"
 #include "modules/vectorfield/processors/vectorfieldrenderer.h"
 #include "modules/vis/processors/slicerenderer3d.h"
 #include "modules/vis/processors/rendertargetcompositor.h"
@@ -68,6 +69,7 @@ namespace campvis {
         LightSourceProvider _lsp;
         MhdImageReader _imageReader;
         MhdImageReader _vectorFieldReader;
+        ParticleFlowRenderer _pfr;
         VectorFieldRenderer _vectorFieldRenderer;
         SliceRenderer3D _sliceRenderer;
         RenderTargetCompositor _rtc;

modules/vectorfield/processors/particleflowrenderer.cpp

+// ================================================================================================
+// 
+// This file is part of the CAMPVis Software Framework.
+// 
+// If not explicitly stated otherwise: Copyright (C) 2012-2014, all rights reserved,
+//      Christian Schulte zu Berge <christian.szb@in.tum.de>
+//      Chair for Computer Aided Medical Procedures
+//      Technische Universitaet Muenchen
+//      Boltzmannstr. 3, 85748 Garching b. Muenchen, Germany
+// 
+// For a full list of authors and contributors, please refer to the file "AUTHORS.txt".
+// 
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file 
+// except in compliance with the License. You may obtain a copy of the License at
+// 
+// http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software distributed under the 
+// License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, 
+// either express or implied. See the License for the specific language governing permissions 
+// and limitations under the License.
+// 
+// ================================================================================================
+
+#include "particleflowrenderer.h"
+
+#include "tgt/buffer.h"
+#include "tgt/tgt_math.h"
+#include "tgt/logmanager.h"
+#include "tgt/shadermanager.h"
+#include "tgt/textureunit.h"
+#include "tgt/vertexarrayobject.h"
+
+#include "core/datastructures/imagedata.h"
+#include "core/datastructures/imagerepresentationgl.h"
+#include "core/datastructures/lightsourcedata.h"
+#include "core/datastructures/geometrydatafactory.h"
+#include "core/datastructures/renderdata.h"
+
+
+namespace campvis {
+
+    const std::string ParticleFlowRenderer::loggerCat_ = "CAMPVis.modules.classification.ParticleFlowRenderer";
+
+    ParticleFlowRenderer::ParticleFlowRenderer(IVec2Property* viewportSizeProp)
+        : VisualizationProcessor(viewportSizeProp)
+        , p_resetButton("ResetButton", "Reset")
+        , p_stepButton("StepButton", "Step")
+        , p_stepInt("StepInt", "Step", 0, 0, 10)
+        , p_inputVectors("InputImage", "Input Image Vectors", "vectors", DataNameProperty::READ)
+        , p_renderOutput("RenderOutput", "Output Image", "ParticleFlowRenderer.output", DataNameProperty::WRITE)
+        , p_arrowSize("ArrowSize", "Arrow Size", 1.f, .001f, 5.f)
+        , p_lenThresholdMin("LenThresholdMin", "Length Threshold Min", .001f, 0.f, 1000.f, 0.005f)
+        , p_lenThresholdMax("LenThresholdMax", "Length Threshold Max", 10.f, 0.f, 10000.f, 10.f)
+        , p_flowProfile1("FlowSpline1", "Flow Profile - Spline 1", 1.f, .0f, 2.f)
+        , p_flowProfile2("FlowSpline2", "Flow Profile - Spline 2", 1.f, .0f, 2.f)
+        , p_flowProfile3("FlowSpline3", "Flow Profile - Spline 3", 1.f, .0f, 2.f)
+        , p_flowProfile4("FlowSpline4", "Flow Profile - Spline 4", 1.f, .0f, 2.f)
+        , p_Time("time", "Time", 0, 0, 100)
+        , p_enableShading("EnableShading", "Enable Shading", true)
+        , p_lightId("LightId", "Input Light Source", "lightsource", DataNameProperty::READ)
+        , p_camera("Camera", "Camera", tgt::Camera())
+        , p_sliceNumber("SliceNumber", "Slice Number", 0, 0, 0)
+        , _arrowGeometry(nullptr)
+        , _shader(nullptr)
+        , _positionBufferA(nullptr)
+        , _positionBufferB(nullptr)
+        , _velocityBufferA(nullptr)
+        , _velocityBufferB(nullptr)
+        , _startTimeBufferA(nullptr)
+        , _startTimeBufferB(nullptr)
+        , _initialPositionBuffer(nullptr)
+        , _vaoA(nullptr)
+        , _vaoB(nullptr)
+    {
+        addProperty(p_resetButton, INVALID_PROPERTIES);
+        addProperty(p_stepButton, INVALID_RESULT | FIRST_FREE_TO_USE_INVALIDATION_LEVEL);
+        addProperty(p_stepInt, INVALID_RESULT | FIRST_FREE_TO_USE_INVALIDATION_LEVEL);
+
+        addProperty(p_inputVectors, INVALID_RESULT | INVALID_PROPERTIES);
+        addProperty(p_renderOutput);
+        addProperty(p_arrowSize);
+        addProperty(p_lenThresholdMin);
+        addProperty(p_lenThresholdMax);
+        addProperty(p_camera);
+        addProperty(p_sliceNumber);
+        addProperty(p_Time);
+        addProperty(p_flowProfile1);
+        addProperty(p_flowProfile2);
+        addProperty(p_flowProfile3);
+        addProperty(p_flowProfile4);
+
+        addProperty(p_enableShading, INVALID_RESULT | INVALID_PROPERTIES | INVALID_SHADER);
+        addProperty(p_lightId);
+    }
+
+    ParticleFlowRenderer::~ParticleFlowRenderer() {
+
+    }
+
+    void ParticleFlowRenderer::init() {
+        VisualizationProcessor::init();
+
+        _shader = ShdrMgr.loadWithCustomGlslVersion("modules/vectorfield/glsl/particleflowrenderer.vert", "", "modules/vectorfield/glsl/particleflowrenderer.frag", generateGlslHeader(), "400");
+        const char* outputNames[] = { "ex_Position", "ex_Velocity", "ex_StartTime" };
+        glTransformFeedbackVaryings(_shader->getID(), 3, outputNames, GL_SEPARATE_ATTRIBS);
+        _shader->linkProgram();
+        tgtAssert(_shader->isLinked(), "Shader not linked!");
+        LGL_ERROR;
+
+        _arrowGeometry = GeometryDataFactory::createArrow(12, 0.35f, 0.05f, 0.09f);
+    }
+
+    void ParticleFlowRenderer::deinit() {
+        ShdrMgr.dispose(_shader);
+
+        delete _arrowGeometry;
+        _arrowGeometry = 0;
+
+        delete _positionBufferA;
+        delete _positionBufferB;
+        delete _velocityBufferA;
+        delete _velocityBufferB;
+        delete _startTimeBufferA;
+        delete _startTimeBufferB;
+        delete _initialPositionBuffer;
+
+        VisualizationProcessor::deinit();
+    }
+
+    void ParticleFlowRenderer::updateResult(DataContainer& dataContainer) {
+        const float frameLength = 0.1f;
+
+        if (_initialPositionBuffer == 0 ) {
+            LERROR("Transform-Feedback buffers not initialized.");
+            return;
+        }
+
+        //GenericImageRepresentationLocal<float, 3>::ScopedRepresentation vectors(dataContainer, p_inputVectors.getValue());
+        ImageRepresentationGL::ScopedRepresentation vectors(dataContainer, p_inputVectors.getValue());
+
+        if (vectors) {
+            ScopedTypedData<LightSourceData> light(dataContainer, p_lightId.getValue());
+
+            if (p_enableShading.getValue() == false || light != nullptr) {
+                const tgt::Camera& cam = p_camera.getValue();
+                const tgt::svec3& imgSize = vectors->getSize();
+                const int sliceNumber = p_sliceNumber.getValue();
+
+                float scale = getTemporalFlowScaling((float)p_Time.getValue() / 100.f,
+                    p_flowProfile1.getValue(),
+                    p_flowProfile2.getValue(),
+                    p_flowProfile3.getValue(),
+                    p_flowProfile4.getValue());
+
+                glEnable(GL_DEPTH_TEST);
+                _shader->activate();
+
+                _shader->setIgnoreUniformLocationError(true);
+                _shader->setUniform("_viewportSizeRCP", 1.f / tgt::vec2(getEffectiveViewportSize()));
+                _shader->setUniform("_projectionMatrix", cam.getProjectionMatrix());
+                _shader->setUniform("_viewMatrix", cam.getViewMatrix());
+
+                if (p_enableShading.getValue() && light != nullptr) {
+                    light->bind(_shader, "_lightSource");
+                }
+                _shader->setIgnoreUniformLocationError(false);
+
+                if (getInvalidationLevel() & FIRST_FREE_TO_USE_INVALIDATION_LEVEL) {
+                    // stage 1: perform 1 step of particle simulation
+                    _shader->selectSubroutine(tgt::ShaderObject::VERTEX_SHADER, "update");
+                    _shader->setUniform("_time", _currentTime);
+                    _shader->setUniform("_frameLength", frameLength);
+                    _shader->setUniform("_lifetime", 10.f);
+
+                    tgt::TextureUnit flowUnit;
+                    vectors->bind(_shader, flowUnit, "_volume", "_volumeTextureParams");
+
+                    glEnable(GL_RASTERIZER_DISCARD);
+                    glBindTransformFeedback(GL_TRANSFORM_FEEDBACK, _feedback[_drawBuffer]);
+
+                    glBeginTransformFeedback(GL_POINTS);
+                        glBindVertexArray((_drawBuffer == 1) ? _vaoA->getId() : _vaoB->getId());
+                        glDrawArrays(GL_POINTS, 0, _numParticles);
+                    glEndTransformFeedback();
+
+                    glBindTransformFeedback(GL_TRANSFORM_FEEDBACK, 0);
+                    glDisable(GL_RASTERIZER_DISCARD);
+
+                    _drawBuffer = 1 - _drawBuffer;
+                    _currentTime += frameLength;
+                    validate(FIRST_FREE_TO_USE_INVALIDATION_LEVEL);
+                    LGL_ERROR;
+                }
+
+                // stage 2: render particles
+                FramebufferActivationGuard fag(this);
+                createAndAttachColorTexture();
+                createAndAttachDepthTexture();
+                glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+
+                _shader->selectSubroutine(tgt::ShaderObject::VERTEX_SHADER, "render");
+                glBindVertexArray((_drawBuffer == 1) ? _vaoA->getId() : _vaoB->getId());
+                glPointSize(10.f);
+                //glDrawTransformFeedback(GL_POINTS, _feedback[1-_drawBuffer]);
+                glDrawArrays(GL_POINTS, 0, _numParticles);
+                glPointSize(1.f);
+
+                _shader->deactivate();
+                glDisable(GL_DEPTH_TEST);
+                LGL_ERROR;
+
+                dataContainer.addData(p_renderOutput.getValue(), new RenderData(_fbo));
+            }
+            else {
+                LDEBUG("Could not load light source from DataContainer.");
+            }
+        }
+        else {
+            LERROR("Could not find suitable input data.");
+        }
+    }
+
+    void ParticleFlowRenderer::updateProperties(DataContainer& dataContainer) {
+        p_lightId.setVisible(p_enableShading.getValue());
+
+        GenericImageRepresentationLocal<float, 3>::ScopedRepresentation vectors(dataContainer, p_inputVectors.getValue());
+
+        if (vectors) {
+            // initialize buffers etc.
+            initializeTransformFeedbackBuffers(vectors);
+        }
+        else {
+            LERROR("No suitable input data found or size of images mismatch!");
+        }
+    }
+
+    void ParticleFlowRenderer::updateShader() {
+        _shader->setHeaders(generateGlslHeader());
+        _shader->rebuild();
+    }
+
+    std::string ParticleFlowRenderer::generateGlslHeader() const {
+        std::string toReturn;
+        if (p_enableShading.getValue())
+            toReturn += "#define ENABLE_SHADING\n";
+
+        return toReturn;
+    }
+
+    void ParticleFlowRenderer::renderVectorArrow(const GenericImageRepresentationLocal<float, 3>* vectors, const tgt::vec3& position, float scale) {
+
+        // avoid overflows
+        if(position.x >= vectors->getSize().x || position.x < 0 ||
+            position.y >= vectors->getSize().y || position.y < 0 ||
+            position.z >= vectors->getSize().z || position.z < 0)
+            return;
+
+        // gather vector direction
+        const tgt::vec3& dir = vectors->getElement(position);
+        float len = tgt::length(dir);
+
+        // threshold
+        if(len < p_lenThresholdMin.getValue() || len > p_lenThresholdMax.getValue())
+            return;
+
+        tgt::vec3 up(0.f, 0.f, 1.f);
+        tgt::vec3 dirNorm = tgt::normalize(dir);
+        tgt::vec3 axis = tgt::cross(up, dirNorm);
+        float dotPr = tgt::dot(up, dirNorm);
+        tgt::mat4 rotationMatrix;
+        if(abs(dotPr-1)<1.e-3f)
+            rotationMatrix = tgt::mat4::identity;
+        else if(abs(dotPr+1)<1.e-3f)
+            rotationMatrix = tgt::mat4::createRotation(tgt::PIf, tgt::vec3(1.f, 0.f, 0.f));
+        else {
+            rotationMatrix = tgt::mat4::createRotation(acos(dotPr), tgt::normalize(axis));
+        }
+
+        const tgt::mat4& voxelToWorldMatrix = vectors->getParent()->getMappingInformation().getVoxelToWorldMatrix();
+
+        // compute model matrix
+        tgt::mat4 modelMatrix = voxelToWorldMatrix * tgt::mat4::createTranslation(position) * rotationMatrix *
+            tgt::mat4::createScale(tgt::vec3(len * p_arrowSize.getValue())) * tgt::mat4::createScale(tgt::vec3(scale));
+
+        // setup shader
+        //_shader->setUniform("_color", tgt::vec4(dirNorm, 1.f));
+        float color = (len - p_lenThresholdMin.getValue()) / (p_lenThresholdMax.getValue() - p_lenThresholdMin.getValue());
+        _shader->setUniform("_color", tgt::vec4(1.f, 1-color, 1-color, 1.f));
+
+        // render single ellipsoid
+        _shader->setUniform("_modelMatrix", modelMatrix);
+        _arrowGeometry->render(GL_TRIANGLE_STRIP);
+    }
+
+
+    float ParticleFlowRenderer::getTemporalFlowScaling(float t, float Ct0, float Ct1, float Ct2, float Ct3)
+    {
+        const float halfPeriod = 0.5f;
+        const float spacing = 0.25f;
+
+        float St[4];
+
+        for(int j = 0; j < 4; ++j) { // iterate over spline positions
+            float splinePos = spacing * (j+1);
+
+            // periodic alignment of samples -> contribution to all splines => dense sampling matrix
+            if(t > splinePos + halfPeriod)
+                t -= 1;
+            else if(t < splinePos - halfPeriod)