Function to write obj files

R/vtk.R

@@ -36,3 +36,56 @@ write_mesh3d_to_vtk <- function(mesh, filename) {
   system(sprintf("head -n 10 %s", filename))
 }
 
+# Write a OBJ file from mesh3d
+write_mesh3d_to_obj <- function(mesh, filename) {
+  if (!inherits(mesh, "mesh3d")) {
+    stop("Input must be a mesh3d object")
+  }
+
+  # Open the file for writing
+  con <- file(filename, "w")
+  on.exit(close(con))  # Ensure the file is closed when the function exits
+
+  # Write vertices
+  vertices <- t(mesh$vb[1:3, ] / mesh$vb[4, ])
+  write(paste("v", vertices[,1], vertices[,2], vertices[,3]), con, sep = "\n")
+
+  # Write texture coordinates if present
+  if (!is.null(mesh$texcoords)) {
+    texcoords <- t(mesh$texcoords)
+    write(paste("vt", texcoords[,1], texcoords[,2]), con, sep = "\n")
+  }
+
+  # Write normals if present
+  if (!is.null(mesh$normals)) {
+    normals <- t(mesh$normals[1:3, ] / mesh$normals[4, ])
+    write(paste("vn", normals[,1], normals[,2], normals[,3]), con, sep = "\n")
+  }
+
+  # Write faces
+  faces <- t(mesh$it)
+  if (!is.null(mesh$texcoords) && !is.null(mesh$normals)) {
+    # Faces with vertex/texture/normal indices
+    write(paste("f",
+                paste(faces[,1], faces[,1], faces[,1], sep="/"),
+                paste(faces[,2], faces[,2], faces[,2], sep="/"),
+                paste(faces[,3], faces[,3], faces[,3], sep="/")), con, sep = "\n")
+  } else if (!is.null(mesh$texcoords)) {
+    # Faces with vertex/texture indices
+    write(paste("f",
+                paste(faces[,1], faces[,1], sep="/"),
+                paste(faces[,2], faces[,2], sep="/"),
+                paste(faces[,3], faces[,3], sep="/")), con, sep = "\n")
+  } else if (!is.null(mesh$normals)) {
+    # Faces with vertex//normal indices
+    write(paste("f",
+                paste(faces[,1], "", faces[,1], sep="/"),
+                paste(faces[,2], "", faces[,2], sep="/"),
+                paste(faces[,3], "", faces[,3], sep="/")), con, sep = "\n")
+  } else {
+    # Faces with only vertex indices
+    write(paste("f", faces[,1], faces[,2], faces[,3]), con, sep = "\n")
+  }
+
+  cat("OBJ file written successfully:", filename, "\n")
+}