we currently have a system to dynamically draw the footprint for each frame onto a 3d globe with elevation. We nwo want to extend this system by a functionality which offers the possibility to visualize the area which was continuesly covered by the footprint (i.e. a footprint path). I am really unsure of how to efficiantly realize this with osgearth. Your help woutld be greatly appreciated.
Yes that was also our idea. But here are my thoughts on that:
1. I am concerned that if we add a polygon for each footprint position, that this will accumulate to so many geometries, that it will evnetually slow down the rendering.
2. What we are aiming for is something that you might still remember from old strategic computer games such as "Command & Conquer", where the player successively discovers the world around him. So at the beginning we want to display the map in black & white. Moving through the world, the footprint of the video should turn the map into color in areas which have been covered.
3. If the world contains 3d objects and the footprint only shows one side of that object, the area occluded by it should still be marked as "unseen". Similar to the Line-Of-Sight example.
I was thinking if this could be realized with Shaders, but I guess one cannot permanently manipulate vertices from within the Shader. One can only manipulate the data for one rendering pass, right? What about stencil buffering or the stencil shadowing. Can that be used in order to achieve our goal? I have not found any documentation or example on how to use the stencil buffer.