Fix clippy lint

src/gpu_buffers.rs

@@ -13,28 +13,60 @@ pub struct VertexBuffer {
 	len: usize,
 }
 
+const FLOAT_SIZE: usize = 4;
+
 impl VertexBuffer {
-	pub fn from_slice (slice: &[f32]) -> Self {
-		const FLOAT_SIZE: usize = 4;
+	// len is the number of floats
 	
-		let id = {
-			let mut id = 0;
+	fn allocate_buffer (len: usize) -> u32 {
+		let mut id = 0;
+		unsafe {
+			gl::GenBuffers (1, &mut id);
+			gl::BindBuffer (gl::ARRAY_BUFFER, id);
+			
+			// Khronos docs say that null is not derefed here
+			gl::BufferData (
+				gl::ARRAY_BUFFER, 
+				(len * FLOAT_SIZE).try_into ().unwrap (), 
+				std::ptr::null (), 
+				gl::STATIC_DRAW
+			);
+		}
+		assert! (id != 0);
+		id
+	}
+	
+	pub fn from_slices (slices: &[&[f32]]) -> Self {
+		let len = slices.iter ()
+		.map (|slice| slice.len ())
+		.sum ();
+		
+		let id = Self::allocate_buffer (len);
+		
+		let mut offset = 0;
+		for slice in slices.iter () {
 			unsafe {
-				gl::GenBuffers (1, &mut id);
-				gl::BindBuffer (gl::ARRAY_BUFFER, id);
-				
-				gl::BufferData (gl::ARRAY_BUFFER, (slice.len () * FLOAT_SIZE).try_into ().unwrap (), &slice [0] as *const f32 as *const c_void, gl::STATIC_DRAW);
+				gl::BufferSubData (
+					gl::ARRAY_BUFFER, 
+					(offset * FLOAT_SIZE).try_into ().unwrap (), 
+					(len * FLOAT_SIZE).try_into ().unwrap (), 
+					&slice [0] as *const f32 as *const c_void
+				);
 			}
-			assert! (id != 0);
-			id
-		};
+			
+			offset += slice.len ();
+		}
 		
 		Self {
 			id,
-			len: slice.len (),
+			len,
 		}
 	}
 	
+	pub fn from_slice (slice: &[f32]) -> Self {
+		Self::from_slices (&[slice])
+	}
+	
 	pub fn bind (&self) {
 		unsafe {
 			gl::BindBuffer (gl::ARRAY_BUFFER, self.id);