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 From:  Michael Gibson
1602.2 In reply to 1602.1 
Hi Steve, the difference is mostly in the overall mesh polygon count.

When you do the export, the export mesher does a much more careful job of trying to create a mesh using as few polygons as possible. This results in quite a bit lower polygon count than the display mesher. Unfortunately the export mesher calculations are very time consuming, so it isn't very practical to use it for the main working display when things need to be meshed all the time.

The display mesher is tuned instead to create the mesh really fast, and it tends to err more on the side of creating additional polygons to get a smoother looking working display.

When you're seeing a significant difference between the "working mode" display mesh and the export mesh display speed, the display mesh is probably something like 5x to 10x the density (in triangle count) of the export mesh.

On top of that, it is a lot more work to display the curved edges in the regular working view. Each straight-line polygon edge that is shown in the export mesh display is a lot less work comparatively. Just displaying 1 curved arc edge may be the equivalent work as displaying 40 straight edges or so. So that particular kind of additional detail that you're talking about in the export display is a fairly inexpensive kind of detail.

If you have a graphics card that is a few years old, you might consider upgrading it to a brand new one. Newer ones are always getting faster at rendering polygons, and that could help to reduce this problem for you when working with larger models.

Other than that, you've found all the pertinent settings under Options / View - turning "Add detail to inflections" off and raising mesh angle to something like 20 are a good idea for heavier scenes, that will significantly reduce the display polygon density.

In the future I would like to try and figure out some better ways of handling this, like it might help if the density was sort of more variable, starting with a rough version and then re-meshing to a denser version only if you zoomed in on a particular piece. But that is a significantly difficult thing to accomplish though.

- Michael