feat(engine): add using element buffers

2 files changed, 56 insertions, 10 deletions

diff --git a/engine/src/opengl/buffer.rs b/engine/src/opengl/buffer.rs
index 34514fd..3a4ecf0 100644
--- a/engine/src/opengl/buffer.rs
+++ b/engine/src/opengl/buffer.rs
@@ -4,13 +4,14 @@ use std::mem::size_of_val;
 use crate::opengl::currently_bound::CurrentlyBound;
 
 #[derive(Debug)]
-pub struct Buffer<Item>
+pub struct Buffer<Item, ModeT: Mode>
 {
     buffer: gl::types::GLuint,
     _item_pd: PhantomData<Item>,
+    _mode_pd: PhantomData<ModeT>,
 }
 
-impl<Item> Buffer<Item>
+impl<Item, ModeT: Mode> Buffer<Item, ModeT>
 {
     pub fn new() -> Self
     {
@@ -23,6 +24,7 @@ impl<Item> Buffer<Item>
         Self {
             buffer,
             _item_pd: PhantomData,
+            _mode_pd: PhantomData,
         }
     }
 
@@ -31,7 +33,7 @@ impl<Item> Buffer<Item>
     pub fn bind(&self, cb: impl FnOnce(CurrentlyBound<'_, Self>))
     {
         unsafe {
-            gl::BindBuffer(gl::ARRAY_BUFFER, self.buffer);
+            gl::BindBuffer(ModeT::GL_ENUM, self.buffer);
         }
 
         // SAFETY: The buffer object is bound above
@@ -46,7 +48,7 @@ impl<Item> Buffer<Item>
         unsafe {
             #[allow(clippy::cast_possible_wrap)]
             gl::BufferData(
-                gl::ARRAY_BUFFER,
+                ModeT::GL_ENUM,
                 size_of_val(items) as gl::types::GLsizeiptr,
                 items.as_ptr().cast(),
                 usage.into_gl(),
@@ -55,7 +57,7 @@ impl<Item> Buffer<Item>
     }
 }
 
-impl<Item> Drop for Buffer<Item>
+impl<Item, ModeT: Mode> Drop for Buffer<Item, ModeT>
 {
     fn drop(&mut self)
     {
@@ -92,3 +94,28 @@ impl Usage
         }
     }
 }
+
+/// Buffer mode.
+pub trait Mode
+{
+    #[doc(hidden)]
+    const GL_ENUM: gl::types::GLenum;
+}
+
+/// Array buffer kind.
+#[derive(Debug)]
+pub struct ArrayKind;
+
+impl Mode for ArrayKind
+{
+    const GL_ENUM: gl::types::GLenum = gl::ARRAY_BUFFER;
+}
+
+/// Element array buffer kind.
+#[derive(Debug)]
+pub struct ElementArrayKind;
+
+impl Mode for ElementArrayKind
+{
+    const GL_ENUM: gl::types::GLenum = gl::ELEMENT_ARRAY_BUFFER;
+}
diff --git a/engine/src/opengl/vertex_array.rs b/engine/src/opengl/vertex_array.rs
index ba2ded2..6b6065c 100644
--- a/engine/src/opengl/vertex_array.rs
+++ b/engine/src/opengl/vertex_array.rs
@@ -1,6 +1,6 @@
 use std::mem::size_of;
 
-use crate::opengl::buffer::Buffer;
+use crate::opengl::buffer::{ArrayKind as ArrayBufferKind, Buffer};
 use crate::opengl::currently_bound::CurrentlyBound;
 use crate::vertex::{Attribute, AttributeComponentType, Vertex};
 
@@ -26,11 +26,11 @@ impl VertexArray
     }
 
     /// Draws the currently bound vertex array.
-    pub fn draw(
+    pub fn draw_arrays(
         _currently_bound: &CurrentlyBound<Self>,
         primitive_kind: PrimitiveKind,
         start_index: u32,
-        index_cnt: u32,
+        cnt: u32,
     )
     {
         unsafe {
@@ -38,14 +38,33 @@ impl VertexArray
             gl::DrawArrays(
                 primitive_kind.into_gl(),
                 start_index as gl::types::GLint,
-                index_cnt as gl::types::GLsizei,
+                cnt as gl::types::GLsizei,
+            );
+        }
+    }
+
+    /// Draws the currently bound vertex array.
+    pub fn draw_elements(
+        _currently_bound: &CurrentlyBound<Self>,
+        primitive_kind: PrimitiveKind,
+        offset: u32,
+        cnt: u32,
+    )
+    {
+        unsafe {
+            #[allow(clippy::cast_possible_wrap)]
+            gl::DrawElements(
+                primitive_kind.into_gl(),
+                cnt as gl::types::GLsizei,
+                gl::UNSIGNED_INT,
+                (offset as gl::types::GLint) as *const _,
             );
         }
     }
 
     pub fn configure_attrs(
         _currently_bound: &CurrentlyBound<Self>,
-        _vert_buf_curr_bound: &CurrentlyBound<Buffer<Vertex>>,
+        _vert_buf_curr_bound: &CurrentlyBound<Buffer<Vertex, ArrayBufferKind>>,
     )
     {
         let mut offset = 0;