{"id":6667,"date":"2022-09-04T13:13:21","date_gmt":"2022-09-04T07:43:21","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-how-to-get-a-list-the-visible-vertices-and-segments-of-a-mesh\/"},"modified":"2022-09-04T13:13:21","modified_gmt":"2022-09-04T07:43:21","slug":"solved-how-to-get-a-list-the-visible-vertices-and-segments-of-a-mesh","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-how-to-get-a-list-the-visible-vertices-and-segments-of-a-mesh\/","title":{"rendered":"[Solved] How to get a list the visible vertices and segments of a mesh"},"content":{"rendered":"

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Face culling<\/strong><\/p>\n

This works only for single convex strict winding rule mesh without holes!<\/p>\n

The idea is that sign of dot product of 2 vectors will tell you if the vectors are opposite or not. So if we have a normal pointing out and view direction their dot should be negative for faces turned towards camera\/viewer.<\/p>\n

As you do not want to render just select visible planar faces\/edges you can do this on CPU<\/strong> side entirely. What you need is to have your mesh in form of planar faces (does not matter if triangles,quads or whatever) so let assume triangles (for more points you just add them to _face<\/code> but for computation still use only v0,v1,v2<\/code>) … Each face should have the vertexes and normal.<\/p>\n

struct _face\n {\n double v0[3],v1[3],v2[3],n[3];\n };\n\nList<_face> mesh;\n<\/code><\/pre>\n
Now the vertexes v0,v1,v2<\/code> you already have. All of them should be ordered in strict winding rule. That means if you look at any face from outside the points should form only CW<\/strong> (clockwise) loop (or only CCW<\/strong> (counter-clockwise) loop). To compute normal you simply exploit cross product which returns vector perpendicular to both operands:<\/p>\n
n = cross(v1-v0,v2-v1) \/\/ cross product\nn = n \/ |n|            \/\/ optional normalize to unit vector\n<\/code><\/pre>\n
If you need the vector math see<\/p>\n