[osg-users] Offscreen rendering of large scenes

[Werner Modenbach]

Hi Philipp,

I'm not sure, if I really understand what you intend to do.

In my case my scene is very complex and I get timeouts on my graphic card.
So I do a rendering into many tiles, each holding a small portion of the scene.
Thus culling avoids transfer of the complete data onto the graphic card.
The tiles are assigned to a quadtree and rendered with paged LOD.

Would that also be a solution for you?

- Werner -

Am 10.12.2019 um 16:42 schrieb Philipp Wagner:
> Hi,
>
> I want to perform an offscreen rendering of a scene that is too large to fit into the GPU memory at once (lots of big textures).
> My idea was to render parts of the scene each in its own frame, and disable the clearing of the depth and color buffer.
> This does work for the color buffer, but the depth buffer seems to be cleared after each frame, which leads to incorrect results (The later parts are drawn over the previous
> ones, even though they are behind the other parts).
>
> The algorithm:
> 1. Create camera/context/...
> 2. Clear the buffers (i.e. Render an empty scene with a clear mask of (GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT)
> 3. Disable buffer clearing
> 4. Render each part in its own frame
>  a. Add part to the scene
>  b. Render
>  c. Remove part from the scene
> 5. Read back color buffer
>
>
> osg::ref_ptr<::osg::Camera> camera = new osg::Camera();
>
> //Here we set the camera orientation/projection matrix
>
> camera->setClearColor(...);
> camera->setGraphicsContext(context);
>
> osg::ref_ptr<osg::Image> img = new osg::Image;
> img->allocateImage(textureWidth, textureHeight, 1, GL_RGBA, GL_UNSIGNED_BYTE);
> camera->attach(osg::Camera::COLOR_BUFFER0, img, numSamples);
> camera->attach(osg::Camera::DEPTH_BUFFER, GL_DEPTH_COMPONENT32);
> camera->setRenderOrder(osg::Camera::PRE_RENDER);
> camera->setRenderTargetImplementation(osg::Camera::RenderTargetImplementation::FRAME_BUFFER_OBJECT);
> camera->setReferenceFrame(osg::Camera::ABSOLUTE_RF);
> camera->setProjectionResizePolicy(osg::Camera::FIXED);
> camera->setViewport(0, 0, img->s(), img->t());
> viewer->addSlave(camera);
>
> camera->setClearMask(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
> viewer->frame();
> camera->setClearMask(0);
> for (auto& item : parts)
> {
>    //Here we create and add the item to the scene...
>        viewer->frame();
>    //Here we remove item from the scene and delete it
> }
>
> Thanks in advance
> Phil
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