[osg-users] Offscreen rendering of large scenes

[Brad Colbert]

Oh darn!  I had a good reply to this :)   Congrat's on the find!

On Thursday, December 12, 2019 at 12:51:02 AM UTC-8, Philipp Wagner wrote:
>
> 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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