Bug - Meshing don't preview any quad/tri's

 From:  Michael Gibson
1563.6 In reply to 1563.4 
Hi Steve, was the one you noticed also on meshing or on just regular working object display?

That particular thing I was talking about here is just specific to the mesh display.

On the regular object display, it is possible for edges to bleed through somewhat more after a boolean - that is a display artifact that is difficult to correct, not an indication of a broken model.

What happens is for all edges and curves, there is a zbias factor that pulls the z values of the edge forward towards the eye point when the edges or curves are rendered. This is so that the edges don't appear to be partially submerged into the surfaces of the object, which would otherwise cause a kind of broken and stippled edge drawing appearance.

If you have areas of your model that have thin walls, it is possible for the zbias value to be greater than that wall thickness, so that can pull those edges forward enough to be visible even though they really shouldn't be.

It is very difficult to balance this because lowering the bias factor too much results in a bad display of all edges, not just those thin wall ones. So right now this is designed to err more on the side of pulling too much rather than pulling too little.

The z bias factor for a brep is calculated relative to the bounding box size of the brep, so that is why it can change after you do a boolean operation, since that can alter the bounding box of the resulting object.

In the future I am hoping to be able to tune this up somewhat and try to avoid drawing "backfacing edges". The thing is, a backfacing edge of a curved object is not as easy to detect or generally deal with on a curved object as it is on a flat object like a polygon. Unlike a polygon a curved edge can have some portion of it backfacing and some part of it front facing, that doesn't happen on the line edge of a polygon.

- Michael