[osg-users] Offscreen rendering of large scenes

[Philipp Wagner]

Sorry, the issue has been that the camera automatically adjusted the near 
and far plane when rendering the individual parts.
Problem solved.

Grettings,
Phil

Am Dienstag, 10. Dezember 2019 16:42:23 UTC+1 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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