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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