feat(engine): add support for Wavefront obj usemtl & mtllib

1 files changed, 118 insertions, 3 deletions

diff --git a/engine/src/file_format/wavefront/obj.rs b/engine/src/file_format/wavefront/obj.rs
index 884229c..7e1629a 100644
--- a/engine/src/file_format/wavefront/obj.rs
+++ b/engine/src/file_format/wavefront/obj.rs
@@ -2,6 +2,8 @@
 //!
 //! File format documentation: <https://paulbourke.net/dataformats/obj>
 
+use std::path::PathBuf;
+
 use crate::color::Color;
 use crate::file_format::wavefront::common::{
     keyword,
@@ -84,6 +86,22 @@ pub fn parse(obj_content: &str) -> Result<Obj, Error>
         })
         .collect::<Result<Vec<_>, _>>()?;
 
+    let material_specifiers = statements
+        .iter()
+        .filter_map(|(line_no, statement)| {
+            if statement.keyword != Keyword::Usemtl {
+                return None;
+            }
+
+            let material_name = try_option!(statement.get_text_arg(0, *line_no));
+
+            Some(Ok(MaterialSpecifier {
+                material_name: material_name.to_string(),
+                line_no: *line_no,
+            }))
+        })
+        .collect::<Result<Vec<_>, _>>()?;
+
     let faces = statements
         .iter()
         .filter_map(|(line_no, statement)| {
@@ -95,15 +113,41 @@ pub fn parse(obj_content: &str) -> Result<Obj, Error>
             let vertex_b = try_option!(statement.get_triplet_arg(1, *line_no)).into();
             let vertex_c = try_option!(statement.get_triplet_arg(2, *line_no)).into();
 
-            Some(Ok([vertex_a, vertex_b, vertex_c]))
+            let material_name =
+                find_material_specifier_for_line_no(&material_specifiers, *line_no)
+                    .map(|material_specifier| material_specifier.material_name.clone());
+
+            Some(Ok(Face {
+                vertices: [vertex_a, vertex_b, vertex_c],
+                material_name,
+            }))
         })
-        .collect::<Result<Vec<[FaceVertex; 3]>, _>>()?;
+        .collect::<Result<Vec<Face>, _>>()?;
+
+    let mtl_libs = statements
+        .iter()
+        .filter_map(|(line_no, statement)| {
+            if statement.keyword != Keyword::Mtllib {
+                return None;
+            }
+
+            let mtl_lib_paths = try_option!(statement
+                .arguments
+                .iter()
+                .enumerate()
+                .map(|(index, value)| Ok(PathBuf::from(value.to_text(index, *line_no)?)))
+                .collect::<Result<Vec<_>, ParsingError>>());
+
+            Some(Ok(mtl_lib_paths))
+        })
+        .collect::<Result<Vec<_>, _>>()?;
 
     Ok(Obj {
         vertex_positions,
         vertex_normals,
         texture_positions,
         faces,
+        mtl_libs,
     })
 }
 
@@ -115,7 +159,8 @@ pub struct Obj
     pub vertex_positions: Vec<Vec3<f32>>,
     pub vertex_normals: Vec<Vec3<f32>>,
     pub texture_positions: Vec<Vec2<f32>>,
-    pub faces: Vec<[FaceVertex; 3]>,
+    pub faces: Vec<Face>,
+    pub mtl_libs: Vec<Vec<PathBuf>>,
 }
 
 impl Obj
@@ -125,6 +170,7 @@ impl Obj
         let vertices = self
             .faces
             .iter()
+            .map(|face| face.vertices.clone())
             .flatten()
             .map(|face_vertex| face_vertex.to_vertex(self))
             .collect::<Result<Vec<_>, Error>>()?;
@@ -134,6 +180,7 @@ impl Obj
             Some(
                 self.faces
                     .iter()
+                    .map(|face| face.vertices.clone())
                     .flatten()
                     .enumerate()
                     .map(|(index, _)| {
@@ -146,6 +193,14 @@ impl Obj
 }
 
 #[derive(Debug)]
+#[non_exhaustive]
+pub struct Face
+{
+    pub vertices: [FaceVertex; 3],
+    pub material_name: Option<String>,
+}
+
+#[derive(Debug, Clone)]
 pub struct FaceVertex
 {
     pub position: u32,
@@ -264,5 +319,65 @@ keyword! {
 
         #[keyword(rename = "f")]
         F,
+
+        #[keyword(rename = "mtllib")]
+        Mtllib,
+
+        #[keyword(rename = "usemtl")]
+        Usemtl,
+    }
+}
+
+#[derive(Debug)]
+struct MaterialSpecifier
+{
+    material_name: String,
+    line_no: usize,
+}
+
+fn find_material_specifier_for_line_no(
+    material_specifiers: &[MaterialSpecifier],
+    line_no: usize,
+) -> Option<&MaterialSpecifier>
+{
+    material_specifiers
+        .iter()
+        .rev()
+        .find(|material_specifier| material_specifier.line_no < line_no)
+}
+
+#[cfg(test)]
+mod tests
+{
+    use super::parse;
+
+    #[test]
+    fn parse_containing_usemtl_works()
+    {
+        let obj = parse(concat!(
+            "usemtl dark-green\n",
+            "f 6/8/1 7/5/3 1/3/2\n",
+            "f 1/2/4 4/1/8 3/4/2\n",
+            "usemtl light-pink\n",
+            "f 9/1/7 5/1/2 3/2/7"
+        ))
+        .expect("Expected Ok");
+
+        assert_eq!(obj.faces.len(), 3);
+
+        assert_eq!(
+            obj.faces[0].material_name.as_ref().expect("Expected Some"),
+            "dark-green"
+        );
+
+        assert_eq!(
+            obj.faces[1].material_name.as_ref().expect("Expected Some"),
+            "dark-green"
+        );
+
+        assert_eq!(
+            obj.faces[2].material_name.as_ref().expect("Expected Some"),
+            "light-pink"
+        );
     }
 }