fix: rotate normals with model to correct helicopter lighting during rotation

shaders/simple.vert

@@ -6,9 +6,10 @@ in layout(location=2) vec3 aNormal;
 out vec4 vColor;
 out vec3 vNormal;
 layout(location = 0) uniform mat4 transform;
+uniform mat3 normalMatrix;
 
 void main() {
     gl_Position = transform * vec4(position, 1.0f);
     vColor = aColor;
-    vNormal = aNormal;
+    vNormal = normalize(normalMatrix * aNormal);
 }

src/main.rs

@@ -130,7 +130,7 @@ unsafe fn create_vao(vertices: &Vec<f32>, normals: &Vec<f32>, colors: &Vec<f32>,
 }
 
 // Scene graph drawing function
-unsafe fn draw_scene(node: &scene_graph::SceneNode, transform_loc: i32, view_projection: &glm::Mat4, transform_so_far: &glm::Mat4) {
+unsafe fn draw_scene(node: &scene_graph::SceneNode, transform_loc: i32, normal_loc: i32, view_projection: &glm::Mat4, transform_so_far: &glm::Mat4) {
     // Build model matrix from node transformations
     let translation = glm::translation(&node.position);
     let rot_x = glm::rotation(node.rotation.x, &glm::vec3(1.0, 0.0, 0.0));
@@ -148,6 +148,9 @@ unsafe fn draw_scene(node: &scene_graph::SceneNode, transform_loc: i32, view_pro
     if node.index_count > 0 {
         let mvp = view_projection * new_transform;
         gl::UniformMatrix4fv(transform_loc, 1, gl::FALSE, mvp.as_ptr());
+        let nm4 = glm::transpose(&glm::inverse(&new_transform));
+        let normal_matrix = glm::mat3(&nm4);
+        gl::UniformMatrix3fv(normal_loc, 1, gl::FALSE, normal_matrix.as_ptr());
         gl::BindVertexArray(node.vao_id);
         gl::DrawElements(gl::TRIANGLES, node.index_count, gl::UNSIGNED_INT, ptr::null());
     }
@@ -349,6 +352,7 @@ fn main() {
         };
         // get uniform location for the matrix (named `transform` in your vertex shader)
         let transform_loc = unsafe { simple_shader.get_uniform_location("transform") };
+        let normal_loc    = unsafe { simple_shader.get_uniform_location("normalMatrix") };
 
         // Used to demonstrate keyboard handling for exercise 2.
         let mut _arbitrary_number = 0.0; // feel free to remove
@@ -460,7 +464,7 @@ fn main() {
 
                 // Draw scene via scene graph
                 let view_proj = projection * view;
-                draw_scene(&*root_node, transform_loc, &view_proj, &glm::identity());
+                draw_scene(&*root_node, transform_loc, normal_loc, &view_proj, &glm::identity());
             }
 
             // Display the new color buffer on the display