From d2b65c8ff1b9a4e74b4940d7f7f32f66f50c4b13 Mon Sep 17 00:00:00 2001
From: Ian Chamberlain <ian.h.chamberlain@gmail.com>
Date: Fri, 24 Nov 2023 22:44:46 -0500
Subject: [PATCH] Add safe wrapper for C3D_BindProgram

---
 citro3d/examples/triangle.rs |  9 ++++-----
 citro3d/src/lib.rs           | 12 +++++++++++-
 citro3d/src/shader.rs        |  8 ++------
 3 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/citro3d/examples/triangle.rs b/citro3d/examples/triangle.rs
index 9412e59..a6a5152 100644
--- a/citro3d/examples/triangle.rs
+++ b/citro3d/examples/triangle.rs
@@ -79,7 +79,8 @@ fn main() {
     let shader = shader::Library::from_bytes(SHADER_BYTES).unwrap();
     let vertex_shader = shader.get(0).unwrap();
 
-    let mut program = shader::Program::new(vertex_shader).unwrap();
+    let program = shader::Program::new(vertex_shader).unwrap();
+    instance.bind_program(&program);
 
     let mut vbo_data = Vec::with_capacity_in(VERTICES.len(), ctru::linear::LinearAllocator);
     vbo_data.extend_from_slice(VERTICES);
@@ -87,7 +88,7 @@ fn main() {
     let mut buf_info = buffer::Info::new();
     let (attr_info, vbo_idx) = prepare_vbos(&mut buf_info, &vbo_data);
 
-    scene_init(&mut program);
+    scene_init();
 
     let projection_uniform_idx = program.get_uniform("projection").unwrap();
 
@@ -191,11 +192,9 @@ fn calculate_projections() -> Projections {
     }
 }
 
-fn scene_init(program: &mut shader::Program) {
+fn scene_init() {
     // Load the vertex shader, create a shader program and bind it
     unsafe {
-        citro3d_sys::C3D_BindProgram(program.as_raw_mut());
-
         // 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);
diff --git a/citro3d/src/lib.rs b/citro3d/src/lib.rs
index a100e31..9368b5c 100644
--- a/citro3d/src/lib.rs
+++ b/citro3d/src/lib.rs
@@ -73,7 +73,8 @@ impl Instance {
     }
 
     /// Render a frame. The passed in function/closure can mutate the instance,
-    /// such as to [select a render target](Self::select_render_target).
+    /// such as to [select a render target](Self::select_render_target)
+    /// or [bind a new shader program](Self::bind_program).
     #[doc(alias = "C3D_FrameBegin")]
     #[doc(alias = "C3D_FrameEnd")]
     pub fn render_frame_with(&mut self, f: impl FnOnce(&mut Self)) {
@@ -139,6 +140,15 @@ impl Instance {
         }
     }
 
+    /// Use the given [`shader::Program`] for subsequent draw calls.
+    pub fn bind_program(&mut self, program: &shader::Program) {
+        // SAFETY: AFAICT C3D_BindProgram just copies pointers from the given program,
+        // instead of mutating the pointee in any way that would cause UB
+        unsafe {
+            citro3d_sys::C3D_BindProgram(program.as_raw().cast_mut());
+        }
+    }
+
     /// Bind a uniform to the given `index` in the vertex shader for the next draw call.
     ///
     /// # Example
diff --git a/citro3d/src/shader.rs b/citro3d/src/shader.rs
index c2042bf..9f1de0b 100644
--- a/citro3d/src/shader.rs
+++ b/citro3d/src/shader.rs
@@ -17,6 +17,7 @@ use crate::uniform;
 ///
 /// The PICA200 does not support user-programmable fragment shaders.
 #[doc(alias = "shaderProgram_s")]
+#[must_use]
 pub struct Program {
     program: ctru_sys::shaderProgram_s,
 }
@@ -102,18 +103,13 @@ impl Program {
     pub(crate) fn as_raw(&self) -> *const ctru_sys::shaderProgram_s {
         &self.program
     }
-
-    // TODO: pub(crate)
-    pub fn as_raw_mut(&mut self) -> *mut ctru_sys::shaderProgram_s {
-        &mut self.program
-    }
 }
 
 impl Drop for Program {
     #[doc(alias = "shaderProgramFree")]
     fn drop(&mut self) {
         unsafe {
-            let _ = ctru_sys::shaderProgramFree(self.as_raw_mut());
+            let _ = ctru_sys::shaderProgramFree(self.as_raw().cast_mut());
         }
     }
 }