Super-fast volume (aka Downscaled Volume Rendering).

include/openspace/rendering/framebufferrenderer.h

@@ -70,6 +70,7 @@ public:
     void updateDeferredcastData();
     void updateHDRAndFiltering();
     void updateFXAA();
+    void updateDownscaledVolume();
     
     void setResolution(glm::ivec2 res) override;
     void setHDRExposure(float hdrExposure) override;
@@ -110,6 +111,8 @@ private:
     void resolveMSAA(float blackoutFactor);
     void applyTMO(float blackoutFactor);
     void applyFXAA();
+    void updateDownscaleColorTexture();
+    void writeDownscaledVolume();
     
     std::map<VolumeRaycaster*, RaycastData> _raycastData;
     RaycasterProgObjMap _exitPrograms;
@@ -122,10 +125,12 @@ private:
     std::unique_ptr<ghoul::opengl::ProgramObject> _hdrFilteringProgram;
     std::unique_ptr<ghoul::opengl::ProgramObject> _tmoProgram;
     std::unique_ptr<ghoul::opengl::ProgramObject> _fxaaProgram;
+    std::unique_ptr<ghoul::opengl::ProgramObject> _downscaledVolumeProgram;
 
     UniformCache(hdrFeedingTexture, blackoutFactor, hdrExposure, gamma,
                  Hue, Saturation, Value) _hdrUniformCache;
     UniformCache(renderedTexture, inverseScreenSize) _fxaaUniformCache;
+    UniformCache(downscaledRenderedVolume) _writeDownscaledVolumeUniformCache;
 
     GLint _defaultFBO;
     GLuint _screenQuad;
@@ -157,6 +162,12 @@ private:
         GLuint fxaaTexture;
     } _fxaaBuffers;
 
+    struct {
+        GLuint framebuffer;
+        GLuint colorTexture;
+        float currentDownscaleFactor  = 1.f;
+    } _downscaleVolumeRendering;
+
     unsigned int _pingPongIndex = 0u;
 
     bool _dirtyDeferredcastData;

include/openspace/rendering/volumeraycaster.h

@@ -128,6 +128,25 @@ public:
      * helper file) which should be a prefix to all symbols defined by the helper
      */
     virtual std::string helperPath() const = 0;
+
+    virtual void setMaxSteps(int nsteps) { _rayCastMaxSteps = nsteps; };
+
+    virtual const int maxSteps() const { return _rayCastMaxSteps;  };
+
+    virtual void setDownscaleRender(float value) { _downscaleRenderConst = value; };
+
+    virtual const float downscaleRender() const { return _downscaleRenderConst; };
+
+private:
+    /**
+     * Maximum number of integration steps to be executed by the volume integrator. 
+     */
+    int _rayCastMaxSteps = 1000;
+
+    /**
+     * Enable and set the downscale rendering of the volume. Used to improve performance.
+     */
+    float _downscaleRenderConst = 1.0f;
 };
 
 } // namespace openspace