R/generate_surface.R

In rayvertex: 3D Software Rasterizer

#' Generate Surface
#' 
#' @keywords internal
generate_surface = function (heightmap, zscale = 1) {
  nr = nrow(heightmap)
  nc = ncol(heightmap)
  vertex_matrix_row = matrix(seq_len(nr) - 1, nrow = nr, ncol = nc) - 
    (nr - 1)/2
  vertex_matrix_col = matrix(seq_len(nc) - 1, nrow = nr, ncol = nc, 
                             byrow = TRUE) - (nc - 1)/2
  row_vert = c(vertex_matrix_row)
  col_vert = c(vertex_matrix_col)
  verts = matrix(c(row_vert, c(heightmap)/zscale, col_vert), 
                 ncol = 3L)
  offset_row_top = matrix(c(0L, nr, 1L), ncol = 3L, nrow = (nr - 
                                                              1L) * (nc - 1L), byrow = TRUE)
  offset_row_bot = matrix(c(1L, nr, nr + 1L), ncol = 3L, nrow = (nr - 
                                                                   1L) * (nc - 1L), byrow = TRUE)
  indices_all = matrix(seq_len(length(heightmap)), nrow = nr, 
                       ncol = nc)
  indices_truncated = indices_all[seq(1L, nr - 1L), seq(1L, 
                                                        nc - 1L)]
  indices_matrix = matrix(c(indices_truncated), ncol = 3L, 
                          nrow = (nr - 1L) * (nc - 1L))
  indices_top_triangle = indices_matrix + offset_row_top
  indices_bot_triangle = indices_matrix + offset_row_bot
  has_no_na = function(x) {
    na_mat = matrix(is.na(verts[x, 2]), ncol = 3L, nrow = length(x)/3L)
    return(na_mat[, 1L] | na_mat[, 2L] | na_mat[, 3L])
  }
  remove_tri_top = has_no_na(indices_top_triangle)
  remove_tri_bot = has_no_na(indices_bot_triangle)
  remove_tri = remove_tri_top | remove_tri_bot
  indices_top_triangle = indices_top_triangle[!remove_tri, 
  ]
  indices_bot_triangle = indices_bot_triangle[!remove_tri, 
  ]
  interleved_triangles = matrix(c(t(cbind(indices_top_triangle, 
                                          indices_bot_triangle))), nrow = 3L)
  verts[is.na(verts[, 2L]), 2L] = mean(verts[, 2L], na.rm = TRUE)
  texcoords_x = matrix(seq(0, 1, length.out = nr), nrow = nr, 
                       ncol = nc, byrow = FALSE)
  texcoords_y = matrix(seq(1, 0, length.out = nc), nrow = nr, 
                       ncol = nc, byrow = TRUE)
  texcoords = matrix(c(c(texcoords_x), c(texcoords_y)), ncol = 2L)
  return(list(verts = verts, inds = interleved_triangles, 
              texcoords = texcoords))
}