to represent ploygons or cube as a collection paticles in opengl

Question

I want to represent cube or polygon as a collection particles, so that it can be divided into spatial grid. The reason behind is that I want to calculate the collision of fluid particle (SPH technique) with solid objects like building, terrain. How can I represent solid objects as collection of particles?

Answer 1

If I get it right you want to achieve something like this:

so just divide your mesh to quads or any other primitives I would do it like this:

1. obtain the points

   just all the global grid points that are inside polygon. You can also add the intersection of grid axises with perimeter polyline so loop through all grid points inside bounding rectangle of polygon and use points that are inside with hit test

   Another option is make something like

   convex polygon rasterizer

   but rasterize with grid step instead of single pixel and store the point coordinates instead of outputing it to image/screen ...

2. quad/triangulate ...

   the inside is straight forward but the perimeter can be a mess. If you ignore perimeter grid points then the problem is much simplified. Connect points according to their coordinates and handle special cases or use any standard triangulation algorithm for these areas.

   The mesh should be a 2D matrix of point/mask that will greatly simplify the coding:

   GLfloat xyz[ys][xs][3];
   bool on[ys][xs];
   

   
   xyz are the coordinates
   on is flag if the point is used or not (inside polygon)
   xs,ys is the grid resolution of the bounding box...

   this way you know which point neighbors which points so the draw is simple (use quad strips ... This representation is also good for the simulation. For volumes use cube grid (like voxels) or just BR model like cube surface grid ...

3. What to do with perimeter multi-points

   on the perimeter there can be more then 1 point per grid position so merge them all together (or use the closest one to grid position). For example see the image on the right side the bottom half. The grid point is outside the polygon creating 2 intersection points. If you merge this to single one then the above structure is still enough