eatgel/eatgel/src/buffer.rs

use crate::types::TypeDescriptor;
use std::ffi::c_void;
use std::ops::Range;

pub struct StaticBufferNonIndexed {
    pub vao: u32,
    pub attributes: Vec<Attribute>,
    pub elements: usize,
}

impl StaticBufferNonIndexed {
    pub fn bind(&self) {
        unsafe {
            gl::BindVertexArray(self.vao);
        }
    }

    pub fn draw(&self) {
        self.bind();

        unsafe { gl::DrawArrays(gl::TRIANGLES, 0, self.elements as i32) }
    }
}

pub struct StaticBuffer {
    pub vao: u32,
    pub attributes: Vec<Attribute>,
    pub ebo: u32,
    pub indices: usize,
}

impl StaticBuffer {
    pub fn bind(&self) {
        unsafe {
            gl::BindVertexArray(self.vao);
            gl::BindBuffer(gl::ELEMENT_ARRAY_BUFFER, self.ebo);
        }
    }

    pub fn draw(&self) {
        self.bind();

        unsafe {
            gl::DrawElements(
                gl::TRIANGLES,
                self.indices as i32,
                gl::UNSIGNED_INT,
                0 as *const c_void,
            )
        }
    }
}

impl Drop for StaticBuffer {
    fn drop(&mut self) {
        unsafe { gl::DeleteVertexArrays(1, [self.vao].as_ptr()) }
    }
}

pub struct Attributes {
    mem: Box<[u8]>,
    pub attributes: Vec<Attribute>,
    pub size: usize,
    pub elements: usize,
}

impl Attributes {
    pub fn as_ptr(&self) -> *const c_void {
        self.mem.as_ptr() as *const c_void
    }
}

pub struct Attribute {
    pub amount: usize,
    pub stride: usize,
    pub offset: usize,
    pub gl_type: u32,
}

pub trait VertexData {
    fn get_sizes() -> Box<[usize]>;
    fn get_types() -> Box<[TypeDescriptor]>;
    fn get_pointers(&self) -> Box<[*const c_void]>;
}

pub trait VertexDataCollection<D>
where
    D: VertexData,
{
    fn get_amount(&self) -> usize;
    fn get_list(&self) -> &[D];
    fn create_ptr(&self, interleaved: bool, range: Option<Range<usize>>) -> Attributes {
        let sizes = D::get_sizes();
        let struct_size = sizes.clone().iter().sum();
        let range = range.unwrap_or(0..self.get_amount());
        let amount = range.end - range.start;
        let mut list = vec![0u8; struct_size * amount];
        let items = self.get_list();

        for i in range.clone() {
            let item = &items[i];
            let pointers = item.get_pointers();
            let sizes_and_pointers = sizes
                .iter()
                .zip(pointers.iter())
                .collect::<Vec<(&usize, &*const c_void)>>();

            let mut offset = 0;

            for (size, ptr) in sizes_and_pointers {
                let index = if interleaved {
                    offset + (struct_size * (i - range.start))
                } else {
                    (offset * amount) + size * i
                };

                unsafe {
                    std::ptr::copy(ptr.cast(), list.as_mut_ptr().add(index), *size);
                }

                offset += size;
            }
        }

        let mut attributes = vec![];
        let mut offset = 0;
        for (size, type_desc) in sizes.iter().zip(D::get_types().iter()) {
            attributes.push(Attribute {
                amount: type_desc.amount as usize,
                gl_type: type_desc.gl_type,
                stride: if interleaved { struct_size } else { *size },
                offset: if interleaved { offset } else { offset * amount },
            });

            offset += *size;
        }

        Attributes {
            mem: list.into_boxed_slice(),
            attributes,
            size: struct_size * amount,
            elements: items.len(),
        }
    }
}

impl<D: VertexData> VertexDataCollection<D> for Vec<D> {
    fn get_amount(&self) -> usize {
        self.len()
    }

    fn get_list(&self) -> &[D] {
        &self
    }
}

impl<D: VertexData> VertexDataCollection<D> for &[D] {
    fn get_amount(&self) -> usize {
        self.len()
    }

    fn get_list(&self) -> &[D] {
        self
    }
}

impl<D: VertexData> VertexDataCollection<D> for Box<[D]> {
    fn get_amount(&self) -> usize {
        self.len()
    }

    fn get_list(&self) -> &[D] {
        &self
    }
}

impl<D: VertexData> VertexDataCollection<D> for [D] {
    fn get_amount(&self) -> usize {
        self.len()
    }

    fn get_list(&self) -> &[D] {
        &self
    }
}