rgl::readOBJ (still not available on osx due to unrelated errors with latest rgl package)

readObj.R

# straight from:
#   https://r-forge.r-project.org/scm/viewvc.php/*checkout*/pkg/rgl/R/obj.R?revision=1197&root=rgl
# see:
#   https://r-forge.r-project.org/scm/viewvc.php/*checkout*/pkg/rgl/DESCRIPTION?revision=1234&root=rgl
# for authorship/license information
readOBJ <- function(con, ...) {
  lines <- readLines(con)
  instrs <- sub(" .*", "", lines)
  vertices <- read.table(textConnection(lines[instrs == "v"]),
                         col.names = c("instr", "x", "y", "z"),
                         colClasses = c(instr = "character", 
                                        x="numeric",
                                        y="numeric",
                                        z="numeric"))
  vertices <- with(vertices, rbind(x, y, z))
  tfaces <- grepl("^f\\W+\\w+\\W+\\w+\\W+\\w+$", lines)
  triangles <- read.table(textConnection(lines[tfaces]),
                      col.names = c("instr", "v1", "v2", "v3"),
                      colClasses = "character")
  triangles <- with(triangles, rbind(v1, v2, v3))
  if (length(grep("/", triangles))) {
    warning("normals and/or textures ignored")
    triangles <- sub("/.*", "", triangles)   
  }
  triangles <- structure(as.numeric(triangles),
                         dim = dim(triangles))
  qfaces <- grepl("^f\\W+\\w+\\W+\\w+\\W+\\w+\\W+\\w+$", lines)
  if (any(qfaces)) {
    quads <- read.table(textConnection(lines[qfaces]),
                        col.names = c("instr", "v1", "v2", "v3", "v4"),
                        colClasses = "character")
    quads <- with(quads, rbind(v1, v2, v3, v4))
    if (length(grep("/", quads))) {
      warning("normals and/or textures ignored")
      quads <- sub("/.*", "", quads)
    }
    quads <- structure(as.numeric(quads), dim = dim(quads))
  }
  others <- strsplit(lines[instrs == "f" & !tfaces & !qfaces], " ")
  # FIXME:  this will be really slow if there are a lot of others
  # Should pre-allocate extra space.
  for (i in seq_along(others)) {
    v <- as.numeric(others[[i]][-1])
    tri <- triangulate(t(vertices[,v]))
    tri <- structure(v[tri], dim = dim(tri))
    triangles <- cbind(triangles, tri)
  }  
  ignored <- unique(instrs)
  ignored <- ignored[!(ignored %in% c("v", "f", "", "#"))]
  if (length(ignored))
    warning("instructions ", paste0('"', ignored, '"', collapse = ", "), " ignored.")
  result <- tmesh3d(vertices, triangles, homogeneous = FALSE, ...)
  if (any(qfaces)) 
    result$ib <- quads
  result
}