1 files changed, 167 insertions, 0 deletions
diff --git a/opengl-bindings/src/buffer.rs b/opengl-bindings/src/buffer.rs
new file mode 100644
index 0000000..c64ec8d
--- /dev/null
+++ b/opengl-bindings/src/buffer.rs
@@ -0,0 +1,167 @@
+use std::marker::PhantomData;
+use std::mem::size_of_val;
+use std::ptr::null;
+
+use safer_ffi::layout::ReprC;
+
+use crate::CurrentContextWithFns;
+
+#[derive(Debug)]
+pub struct Buffer<Item: ReprC>
+{
+    buf: crate::sys::types::GLuint,
+    _pd: PhantomData<Item>,
+}
+
+impl<Item: ReprC> Buffer<Item>
+{
+    #[must_use]
+    pub fn new(current_context: &CurrentContextWithFns<'_>) -> Self
+    {
+        let mut buffer = crate::sys::types::GLuint::default();
+
+        unsafe {
+            current_context.fns().CreateBuffers(1, &raw mut buffer);
+        };
+
+        Self { buf: buffer, _pd: PhantomData }
+    }
+
+    /// Stores items in this buffer.
+    ///
+    /// # Errors
+    /// Returns `Err` if the total size (in bytes) is too large.
+    pub fn store(
+        &self,
+        current_context: &CurrentContextWithFns<'_>,
+        items: &[Item],
+        usage: Usage,
+    ) -> Result<(), Error>
+    {
+        let total_size = size_of_val(items);
+
+        let total_size: crate::sys::types::GLsizeiptr =
+            total_size
+                .try_into()
+                .map_err(|_| Error::TotalItemsSizeTooLarge {
+                    total_size,
+                    max_total_size: crate::sys::types::GLsizeiptr::MAX as usize,
+                })?;
+
+        unsafe {
+            current_context.fns().NamedBufferData(
+                self.buf,
+                total_size,
+                items.as_ptr().cast(),
+                usage.into_gl(),
+            );
+        }
+
+        Ok(())
+    }
+
+    /// Maps the values in the `values` slice into `Item`s which is stored into this
+    /// buffer.
+    ///
+    /// # Errors
+    /// Returns `Err` if the total size (in bytes) is too large.
+    pub fn store_mapped<Value>(
+        &self,
+        current_context: &CurrentContextWithFns<'_>,
+        values: &[Value],
+        usage: Usage,
+        mut map_func: impl FnMut(&Value) -> Item,
+    ) -> Result<(), Error>
+    {
+        let item_size: crate::sys::types::GLsizeiptr = const {
+            assert!(size_of::<Item>() <= crate::sys::types::GLsizeiptr::MAX as usize);
+
+            size_of::<Item>().cast_signed()
+        };
+
+        let total_size = size_of::<Item>() * values.len();
+
+        let total_size: crate::sys::types::GLsizeiptr =
+            total_size
+                .try_into()
+                .map_err(|_| Error::TotalItemsSizeTooLarge {
+                    total_size,
+                    max_total_size: crate::sys::types::GLsizeiptr::MAX as usize,
+                })?;
+
+        unsafe {
+            current_context.fns().NamedBufferData(
+                self.buf,
+                total_size,
+                null(),
+                usage.into_gl(),
+            );
+        }
+
+        for (index, value) in values.iter().enumerate() {
+            let item = map_func(value);
+
+            let offset = index * size_of::<Item>();
+
+            let Ok(offset_casted) = crate::sys::types::GLintptr::try_from(offset) else {
+                unreachable!(); // Reason: The total size can be casted to a GLintptr
+                                // (done above) so offsets should be castable as well
+            };
+
+            unsafe {
+                current_context.fns().NamedBufferSubData(
+                    self.buf,
+                    offset_casted,
+                    item_size,
+                    (&raw const item).cast(),
+                );
+            }
+        }
+
+        Ok(())
+    }
+
+    pub(crate) fn object(&self) -> crate::sys::types::GLuint
+    {
+        self.buf
+    }
+}
+
+/// Buffer usage.
+#[derive(Debug)]
+pub enum Usage
+{
+    /// The buffer data is set only once and used by the GPU at most a few times.
+    Stream,
+
+    /// The buffer data is set only once and used many times.
+    Static,
+
+    /// The buffer data is changed a lot and used many times.
+    Dynamic,
+}
+
+impl Usage
+{
+    fn into_gl(self) -> crate::sys::types::GLenum
+    {
+        match self {
+            Self::Stream => crate::sys::STREAM_DRAW,
+            Self::Static => crate::sys::STATIC_DRAW,
+            Self::Dynamic => crate::sys::DYNAMIC_DRAW,
+        }
+    }
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error
+{
+    #[error(
+        "Total size of items ({total_size}) is too large. Must be < {max_total_size}"
+    )]
+    TotalItemsSizeTooLarge
+    {
+        total_size: usize,
+        max_total_size: usize,
+    },
+}