refactor(engine): add OpenGL object currently bound guards

5 files changed, 70 insertions, 12 deletions

diff --git a/engine/src/currently_bound.rs b/engine/src/currently_bound.rs
new file mode 100644
index 0000000..eefa239
--- /dev/null
+++ b/engine/src/currently_bound.rs
@@ -0,0 +1,22 @@
+use std::marker::PhantomData;
+
+/// A token signifying a OpenGL object is currently bound.
+pub struct CurrentlyBound<'token, Object>
+{
+    _token: PhantomData<&'token Object>,
+}
+
+impl<'token, Object> CurrentlyBound<'token, Object>
+{
+    /// Returns a new `CurrentlyBound`.
+    ///
+    /// # Safety
+    /// A object must actually be currently bound. Otherwise, UB can occur.
+    #[must_use]
+    pub unsafe fn new() -> Self
+    {
+        Self {
+            _token: PhantomData,
+        }
+    }
+}
diff --git a/engine/src/lib.rs b/engine/src/lib.rs
index b93a0bb..5b313ec 100644
--- a/engine/src/lib.rs
+++ b/engine/src/lib.rs
@@ -10,6 +10,7 @@ mod renderer;
 mod shader;
 
 pub mod color;
+pub mod currently_bound;
 pub mod object;
 pub mod vector;
 pub mod vertex;
diff --git a/engine/src/renderer/mod.rs b/engine/src/renderer/mod.rs
index 364b7f4..a23d5a0 100644
--- a/engine/src/renderer/mod.rs
+++ b/engine/src/renderer/mod.rs
@@ -45,7 +45,9 @@ pub fn render<'renderable>(renderables: impl IntoIterator<Item = &'renderable Re
     for renderable in renderables {
         renderable.shader_program.activate();
 
-        renderable.vertex_arr.draw(PrimitiveKind::Triangles, 0, 3);
+        renderable.vertex_arr.bind(|vert_arr_curr_bound| {
+            VertexArray::draw(&vert_arr_curr_bound, PrimitiveKind::Triangles, 0, 3);
+        });
     }
 }
 
@@ -64,14 +66,15 @@ impl Renderable
     pub fn new(shader_program: crate::shader::Program, vertices: &[Vertex]) -> Self
     {
         let vertex_arr = VertexArray::new();
-
-        vertex_arr.bind();
-
         let vertex_buffer = VertexBuffer::new();
 
-        vertex_buffer.store(vertices, BufferUsage::Static);
+        vertex_arr.bind(|vert_arr_curr_bound| {
+            vertex_buffer.bind(|vert_buf_curr_bound| {
+                VertexBuffer::store(&vert_buf_curr_bound, vertices, BufferUsage::Static);
 
-        VertexArray::configure_attrs();
+                VertexArray::configure_attrs(&vert_arr_curr_bound, &vert_buf_curr_bound);
+            });
+        });
 
         Self {
             shader_program,
diff --git a/engine/src/renderer/vertex_array.rs b/engine/src/renderer/vertex_array.rs
index b0aac81..2bd6a5b 100644
--- a/engine/src/renderer/vertex_array.rs
+++ b/engine/src/renderer/vertex_array.rs
@@ -1,5 +1,7 @@
 use std::mem::size_of;
 
+use crate::currently_bound::CurrentlyBound;
+use crate::renderer::vertex_buffer::VertexBuffer;
 use crate::vertex::{Attribute, AttributeComponentType, Vertex};
 
 const VERTEX_STRIDE: usize = size_of::<Vertex>();
@@ -23,10 +25,14 @@ impl VertexArray
         Self { array }
     }
 
-    pub fn draw(&self, primitive_kind: PrimitiveKind, start_index: u32, index_cnt: u32)
+    /// Draws the currently bound vertex array.
+    pub fn draw(
+        _currently_bound: &CurrentlyBound<Self>,
+        primitive_kind: PrimitiveKind,
+        start_index: u32,
+        index_cnt: u32,
+    )
     {
-        self.bind();
-
         unsafe {
             #[allow(clippy::cast_possible_wrap)]
             gl::DrawArrays(
@@ -37,7 +43,10 @@ impl VertexArray
         }
     }
 
-    pub fn configure_attrs()
+    pub fn configure_attrs(
+        _currently_bound: &CurrentlyBound<Self>,
+        _vert_buf_curr_bound: &CurrentlyBound<VertexBuffer>,
+    )
     {
         let mut offset = 0;
 
@@ -50,9 +59,16 @@ impl VertexArray
         }
     }
 
-    pub fn bind(&self)
+    #[allow(clippy::inline_always)]
+    #[inline(always)]
+    pub fn bind(&self, cb: impl FnOnce(CurrentlyBound<'_, Self>))
     {
         unsafe { gl::BindVertexArray(self.array) }
+
+        // SAFETY: A vertex array object is currently bound
+        let currently_bound = unsafe { CurrentlyBound::new() };
+
+        cb(currently_bound);
     }
 
     fn vertex_attrib_ptr(vertex_attr: &Attribute, offset: usize)
diff --git a/engine/src/renderer/vertex_buffer.rs b/engine/src/renderer/vertex_buffer.rs
index 27ed705..57debc3 100644
--- a/engine/src/renderer/vertex_buffer.rs
+++ b/engine/src/renderer/vertex_buffer.rs
@@ -1,5 +1,6 @@
 use std::mem::size_of_val;
 
+use crate::currently_bound::CurrentlyBound;
 use crate::vertex::Vertex;
 
 #[derive(Debug)]
@@ -21,12 +22,27 @@ impl VertexBuffer
         Self { buffer }
     }
 
-    pub fn store(&self, vertices: &[Vertex], usage: BufferUsage)
+    #[allow(clippy::inline_always)]
+    #[inline(always)]
+    pub fn bind(&self, cb: impl FnOnce(CurrentlyBound<'_, Self>))
     {
         unsafe {
             gl::BindBuffer(gl::ARRAY_BUFFER, self.buffer);
         }
 
+        // SAFETY: A vertex array object is currently bound
+        let currently_bound = unsafe { CurrentlyBound::new() };
+
+        cb(currently_bound);
+    }
+
+    /// Stores vertices in the currently bound vertex bound.
+    pub fn store(
+        _currently_bound: &CurrentlyBound<Self>,
+        vertices: &[Vertex],
+        usage: BufferUsage,
+    )
+    {
         unsafe {
             #[allow(clippy::cast_possible_wrap)]
             gl::BufferData(