[osg-users] Visual flicker when using multi-pass technique, related to frustum?

[Robert Osfield]

Hi Hartwig,

In principle what you are doing should work, the project and modelview
matrix by default should be inherited down correctly - there shouldn't
be a frame delay.

The only thing that looks like it could cause problem is that you
switch off the compute near/far for the slave camera but not the
master camera, try doing it for both.

Robert.

On 7 January 2017 at 18:21, Hartwig Wiesmann
<hartwig.wiesmann at skywind.eu> wrote:
> Hi,
>
> I have two graphs that have completely different content. One is used for initialising the depth buffer, the other one for showing the scene.
>
> Code:
> visibleGraphPtr = ...
> depthGraphPtr = ...
> depthGraphPtr->getOrCreateStateSet()->setAttributeAndModes(new osg::ColorMask(false,false,false,false)); // does not use the color buffer
>
>
>
> I use two cameras, one for rendering to the depth buffer, the other one (viewer's main camera) for generating the scene.
>
> Code:
> osg::Camera* renderToDepthCamera(new osg::Camera());
>
> renderToDepthCamera->addChild(depthGraphPtr);
> renderToDepthCamera->setClearMask(GL_DEPTH_BUFFER_BIT);
> renderToDepthCamera->setComputeNearFarMode(osg::CullSettings::DO_NOT_COMPUTE_NEAR_FAR);
> renderToDepthCamera->setGraphicsContext(viewer->getCamera()->getGraphicsContext());
> renderToDepthCamera->setRenderOrder(osg::Camera::PRE_RENDER);
> renderToDepthCamera->setViewport(viewer->getCamera()->getViewport());
> viewer->addSlave(renderToDepthCamera,false);
>
> viewer->getCamera()->setClearMask(GL_COLOR_BUFFER_BIT); // use also depth buffer from pre-rendering
> viewer->setSceneData(visibleGraphPtr);
>
>
>
>
> Basically this setup works. The only problem is that flickering can be seen when zooming into and out of the scene or moving the scene.
>
> My explanation is that the camera rendering to the depth buffer is using a different frustum (namely the old one (one frame old) from the main camera) than the main camera rendering the visible graph.
>
> Is there a possibility to eliminate the flicker without using a third render path at the beginning just to calculate the final frustum?
>
> I could have implemented the same by using a RTT camera and some shader code afterwards but I think that this does not make any difference with respect to flicker, or?
>
> Any suggestions? Thank you!
>
> Cheers,
> Hartwig
>
> ------------------
> Read this topic online here:
> http://forum.openscenegraph.org/viewtopic.php?p=69919#69919
>
>
>
>
>
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