ENH: Format: Add ModelIO support on macOS

Github pull request: #2439

Change-Id: I4464a735a0a20b3e8103a344a64500b3d14b70e6

src/libslic3r/Format/ModelIO.hpp

@@ -0,0 +1,19 @@
+#include <string>
+
+namespace Slic3r {
+    /**
+     * Uses ModelIO to convert supported model types to a temporary STL
+     * that can then be consumed by the existing STL loader
+     * @param input_file The File to load
+     * @return Path to the temporary file, or an empty string if conversion failed
+     */
+    std::string make_temp_stl_with_modelio(const std::string &input_file);
+
+    /**
+     * Convenience function to delete the file.
+     * No return value since success isn't required
+     * @param temp_file File path to delete
+     */
+    void delete_temp_file(const std::string &temp_file);
+}
+

src/libslic3r/Format/ModelIO.mm

@@ -0,0 +1,27 @@
+#include "ModelIO.hpp"
+#import <ModelIO/ModelIO.h>
+
+namespace Slic3r {
+
+    std::string make_temp_stl_with_modelio(const std::string &input_file)
+    {
+        NSURL    *input_url = [NSURL fileURLWithPath:[NSString stringWithUTF8String:input_file.c_str()]];
+        MDLAsset *asset     = [[MDLAsset alloc] initWithURL:input_url];
+
+        NSString *tmp_file_name = [[[NSUUID UUID] UUIDString] stringByAppendingPathExtension:@"stl"];
+        NSURL    *tmp_file_url  = [NSURL fileURLWithPath:[NSTemporaryDirectory() stringByAppendingPathComponent:tmp_file_name]];
+
+        if ([asset exportAssetToURL:tmp_file_url]) {
+            std::string output_file = std::string([[tmp_file_url path] UTF8String]);
+            return output_file;
+        }
+
+        return std::string();
+    }
+    void delete_temp_file(const std::string &temp_file)
+    {
+        NSString *file_path = [NSString stringWithUTF8String:temp_file.c_str()];
+        [[NSFileManager defaultManager] removeItemAtPath:file_path error:NULL];
+    }
+
+} // namespace Slic3r