[osg-users] Dynamically change the "persistence" of the motion blur example

[William Hart]

Hi,

I've been using the Accumulation buffer to apply motion blur to point cloud 
animations, directly taken from the osgMotionBlur example, where the motion 
blur is applied to each window as an osg::Operation.  What I'd like to be able 
to do is dynamically change the amount of blur by varying the persistence 
parameter.  I've poked around the API and found that I can remove the motion 
blur operation with a removeAllOperations call then reapply the motion blur 
with a different persistence value, but this causes the accumulation buffer to 
be cleared.  I can't see any other way to access the Operator once its been 
applied.

Below is the code, 

#include <osgViewer/ViewerBase>
#include <osgViewer/Viewer>
#include <iostream>

class MotionBlurOperation: public osg::Operation
{
public:
    MotionBlurOperation(double persistence):
        osg::Operation("MotionBlur",true),
        cleared_(false),
        persistence_(persistence)
    {
    }

    virtual void operator () (osg::Object* object)
    {
        osg::GraphicsContext* gc = dynamic_cast<osg::GraphicsContext*>(object);
        if (!gc) return;
    
        double t = gc->getState()->getFrameStamp()->getSimulationTime();

        if (!cleared_)
        {
            // clear the accumulation buffer
            glClearColor(0, 0, 0, 0);
            glClear(GL_ACCUM_BUFFER_BIT);
            cleared_ = true;
            t0_ = t;
        }

        double dt = fabs(t - t0_);
        t0_ = t;

        // compute the blur factor
        double s = powf(0.2, dt / persistence_);

        // scale, accumulate and return
        glAccum(GL_MULT, s);
        glAccum(GL_ACCUM, 1 - s);
        glAccum(GL_RETURN, 1.0f);
    }

private:
    bool cleared_;
    double t0_;
    double persistence_;
};

void motionblur(osgViewer::GraphicsWindow* w, double persistence) {
  w->add(new MotionBlurOperation(persistence));
}

any ideas ?

thanks in advance

Bill
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