TrianglePointsInGrid.js

// This calculates the triangle points in a rectangle grid.
// Used for 3D Webgl texture mapping.
// Copyright Joshua Langley 2019.

var rows=4;
var cols=4;
var LRs=2;
var triPoints = 6;
var grid = rows*cols;
var totalTris = grid*LRs;
var pos = [totalTris*triPoints];
var p1,p2;
var c,d;
var offset;
var index = 0;
var mpOffset = 1;
for (var row = 0; row < rows; ++row)
{
  p2 = mpOffset / rows / 2;
  offsetY = row * (mpOffset / rows) + (mpOffset / rows / 2);
  for (var col = 0; col < cols; ++col)
  {
    p1 = mpOffset / cols / 2;
    offsetX = col * (mpOffset / cols) + (mpOffset / cols / 2);

    for (var LR = 0; LR < LRs; ++LR)
    {
      c = (LR % 2 == 0) ? -p1 :  p1;
      d = (LR % 2 == 1) ? -p2 :  p2;

      pos[index+0] = (offsetX - p1);
      pos[index+1] = (offsetY - p2);
      pos[index+2] = (offsetX + p1);
      pos[index+3] = (offsetY + p2);
      pos[index+4] = (offsetX + c );
      pos[index+5] = (offsetY + d );
      index += triPoints;
    }
  }
}
log.info("pos="+JSON.stringify(pos));

Updated - To fix grids higher than 2x2, and grids with different amounts of rows and columns.