Use the lifetime of the input VBO data

We can return a "handle" that stores the index + size of the VBO data,
as well as keeping a phantom borrow on the original data. By requiring
this handle as input during the call to draw arrays, we ensure the VBO
data lives long enough for the draw call.

citro3d/examples/triangle.rs

@@ -1,7 +1,7 @@
 #![feature(allocator_api)]
 
 use citro3d::attrib::{self, AttrInfo};
-use citro3d::buffers::BufInfo;
+use citro3d::buffers::{self, BufInfo};
 use citro3d::render::{ClearFlags, Target};
 use citro3d::{include_aligned_bytes, shader};
 use citro3d_sys::C3D_Mtx;
@@ -81,8 +81,9 @@ fn main() {
 
     let mut vbo_data = Vec::with_capacity_in(VERTICES.len(), ctru::linear::LinearAllocator);
     vbo_data.extend_from_slice(VERTICES);
+    let vbo_idx = prepare_vbos(&vbo_data);
 
-    let (uloc_projection, projection) = scene_init(&mut program, &vbo_data);
+    let (uloc_projection, projection) = scene_init(&mut program);
 
     while apt.main_loop() {
         hid.scan_input();
@@ -99,7 +100,17 @@ fn main() {
 
                 let clear_color: u32 = 0x7F_7F_7F_FF;
                 target.clear(ClearFlags::ALL, clear_color, 0);
-                scene_render(uloc_projection.into(), &projection);
+
+                unsafe {
+                    // Update the uniforms
+                    citro3d_sys::C3D_FVUnifMtx4x4(
+                        ctru_sys::GPU_VERTEX_SHADER,
+                        uloc_projection.into(),
+                        &projection,
+                    );
+                }
+
+                target.draw_arrays(buffers::Primitive::Triangles, vbo_idx);
             });
         };
 
@@ -108,18 +119,7 @@ fn main() {
     }
 }
 
-fn scene_init(program: &mut shader::Program, vbo_data: &[Vertex]) -> (i8, C3D_Mtx) {
-    // Load the vertex shader, create a shader program and bind it
-    unsafe {
-        citro3d_sys::C3D_BindProgram(program.as_raw());
-
-        // Get the location of the uniforms
-        let projection_name = CStr::from_bytes_with_nul(b"projection\0").unwrap();
-        let uloc_projection = ctru_sys::shaderInstanceGetUniformLocation(
-            (*program.as_raw()).vertexShader,
-            projection_name.as_ptr(),
-        );
-
+fn prepare_vbos(vbo_data: &[Vertex]) -> buffers::Index {
     // Configure attributes for use with the vertex shader
     let mut attr_info = AttrInfo::get_mut().expect("failed to get global attr info");
 
@@ -138,20 +138,27 @@ fn scene_init(program: &mut shader::Program, vbo_data: &[Vertex]) -> (i8, C3D_Mt
         .add_loader(reg1, attrib::Format::Float, 3)
         .unwrap();
 
-        eprintln!(
-            "count {} permutation {:#x}",
-            attr_info.count(),
-            attr_info.permutation()
-        );
-
     attr_info
         .set_permutation(&[position_attr, color_attr])
         .unwrap();
 
-        eprintln!(
-            "count {} permutation {:#x}",
-            attr_info.count(),
-            attr_info.permutation()
+    // Configure buffers
+    let mut buf_info = BufInfo::get_mut().unwrap();
+    let buf_idx = buf_info.add(vbo_data, &attr_info).unwrap();
+
+    buf_idx
+}
+
+fn scene_init(program: &mut shader::Program) -> (i8, C3D_Mtx) {
+    // Load the vertex shader, create a shader program and bind it
+    unsafe {
+        citro3d_sys::C3D_BindProgram(program.as_raw());
+
+        // Get the location of the uniforms
+        let projection_name = CStr::from_bytes_with_nul(b"projection\0").unwrap();
+        let uloc_projection = ctru_sys::shaderInstanceGetUniformLocation(
+            (*program.as_raw()).vertexShader,
+            projection_name.as_ptr(),
         );
 
         // Compute the projection matrix
@@ -171,10 +178,6 @@ fn scene_init(program: &mut shader::Program, vbo_data: &[Vertex]) -> (i8, C3D_Mt
             projection.assume_init()
         };
 
-        // Configure buffers
-        let mut buf_info = BufInfo::get_mut().unwrap();
-        buf_info.add(vbo_data, &attr_info).unwrap();
-
         // Configure the first fragment shading substage to just pass through the vertex color
         // See https://www.opengl.org/sdk/docs/man2/xhtml/glTexEnv.xml for more insight
         let env = citro3d_sys::C3D_GetTexEnv(0);
@@ -191,20 +194,3 @@ fn scene_init(program: &mut shader::Program, vbo_data: &[Vertex]) -> (i8, C3D_Mt
         (uloc_projection, projection)
     }
 }
-
-fn scene_render(uloc_projection: i32, projection: &C3D_Mtx) {
-    unsafe {
-        // Update the uniforms
-        citro3d_sys::C3D_FVUnifMtx4x4(ctru_sys::GPU_VERTEX_SHADER, uloc_projection, projection);
-
-        // Draw the VBO
-        citro3d_sys::C3D_DrawArrays(
-            ctru_sys::GPU_TRIANGLES,
-            0,
-            VERTICES
-                .len()
-                .try_into()
-                .expect("VERTICES.len() fits in i32"),
-        );
-    }
-}

citro3d/src/buffers.rs

@@ -1,3 +1,4 @@
+use std::marker::PhantomData;
 use std::ops::{Deref, DerefMut};
 use std::sync::{LazyLock, RwLock};
 
@@ -22,6 +23,33 @@ pub struct BufInfo {
 unsafe impl Sync for BufInfo {}
 unsafe impl Send for BufInfo {}
 
+// TODO: is this a good name? It's more like a "handle" to the VBO data, or a slice.
+#[derive(Debug, Clone, Copy)]
+pub struct Index<'vbo> {
+    index: libc::c_int,
+    size: libc::c_int,
+    _data: PhantomData<&'vbo ()>,
+}
+
+impl Index<'_> {
+    pub fn as_raw(&self) -> libc::c_int {
+        self.index
+    }
+
+    pub fn size(&self) -> libc::c_int {
+        self.size
+    }
+}
+
+#[repr(u32)]
+#[derive(Debug, Clone, Copy)]
+pub enum Primitive {
+    Triangles = ctru_sys::GPU_TRIANGLES,
+    TriangleStrip = ctru_sys::GPU_TRIANGLE_STRIP,
+    TriangleFan = ctru_sys::GPU_TRIANGLE_FAN,
+    GeometryPrim = ctru_sys::GPU_GEOMETRY_PRIM,
+}
+
 impl BufInfo {
     /// Get a reference to the global buffer info.
     pub fn get() -> crate::Result<impl Deref<Target = Self>> {
@@ -33,12 +61,16 @@ impl BufInfo {
         Ok(BUF_INFO.try_write()?)
     }
 
-    pub fn add<T>(&mut self, vbo_data: &[T], attrib_info: &attrib::AttrInfo) -> crate::Result<()> {
+    pub fn add<'vbo, T>(
+        &mut self,
+        vbo_data: &'vbo [T],
+        attrib_info: &attrib::AttrInfo,
+    ) -> crate::Result<Index<'vbo>> {
         let stride = std::mem::size_of::<T>().try_into()?;
         let attrib_count = attrib_info.count();
         let permutation = attrib_info.permutation();
 
-        unsafe {
+        let res = unsafe {
             citro3d_sys::BufInfo_Add(
                 self.raw,
                 // TODO: figure out how the hell to encode the lifetime of this
@@ -47,9 +79,17 @@ impl BufInfo {
                 stride,
                 attrib_count,
                 permutation,
-            );
-        }
+            )
+        };
 
-        Ok(())
+        if res < 0 {
+            Err(crate::Error::System(res))
+        } else {
+            Ok(Index {
+                index: res,
+                size: vbo_data.len().try_into()?,
+                _data: PhantomData,
+            })
+        }
     }
 }

citro3d/src/render.rs

@@ -10,7 +10,7 @@ use ctru::gfx::Screen;
 use ctru::services::gspgpu::FramebufferFormat;
 use ctru_sys::{GPU_COLORBUF, GPU_DEPTHBUF};
 
-use crate::{Error, Result};
+use crate::{buffers, Error, Result};
 
 mod transfer;
 
@@ -91,6 +91,16 @@ impl<'screen> Target<'screen> {
     pub(crate) fn as_raw(&self) -> *mut C3D_RenderTarget {
         self.raw
     }
+
+    pub fn draw_arrays(&mut self, primitive: buffers::Primitive, index: buffers::Index) {
+        unsafe {
+            citro3d_sys::C3D_DrawArrays(
+                primitive as ctru_sys::GPU_Primitive_t,
+                index.as_raw(),
+                index.size(),
+            );
+        }
+    }
 }
 
 bitflags::bitflags! {