Synchronized offscreen rendering

[nolankramer]

If one wanted to render offscreen (say, with a different set of shaders), but maintain the same camera/view of the scene - what is the best approach?

I looked at the vsgExamples/vsgoffscreenshot example, but that showed creating a new camera with a different perspective matrix (to account for a difference in resolution). I assume this is to account for DPI aspect differences?

Is it necessary to create a camera per view (and thus, per RenderGraph)? Is it possible to share a View between RenderGraphs? (forgive the naivete, I did look at the source - but there's quite a bit of intricate code).

Also, I'm curious about the best time to handle resizing the Framebuffer and Image/ImageView? I current attach a Visitor to the viewer with addEventHandler that handles the vsg::ConfigureWindowEvent, but I wonder if this is too late/early? In the vsgoffscreenshot example, I see that resizing is done in the main loop just before update().

[robertosfield]

If you want to share the same viewpoint but have everything else different then just share the ViewMatrix between the Camera or the separate RenderGraph/View.

[dov]

The way I did it was by creating a "tracking transform" as follows:

class TrackingTransform : public vsg::Inherit<vsg::Transform, TrackingTransform>
{
public:
    TrackingTransform(vsg::ref_ptr<vsg::Transform> _other)
        : other(_other) {}

    vsg::dmat4 transform(const vsg::dmat4& mv) const override {
        return other->transform(mv);
    }

private:
    vsg::ref_ptr<vsg::Transform> other;
};
:
auto offscreenTransform = TrackingTransform::create(transform);