From 6623963a7f7a78d4f012bc1e830a320f4c2f1d6f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bel=C3=A9n=20Albeza?= <belen@hey.com>
Date: Mon, 2 Dec 2024 17:35:49 +0100
Subject: [PATCH] :sparkles: Use a static Vec<u8> to handle shared memory

---
 frontend/src/app/render_wasm/api.cljs |  1 -
 render-wasm/src/main.rs               | 13 +++++-------
 render-wasm/src/mem.rs                | 30 +++++++++++++++++----------
 3 files changed, 24 insertions(+), 20 deletions(-)

diff --git a/frontend/src/app/render_wasm/api.cljs b/frontend/src/app/render_wasm/api.cljs
index 33b32fd57b..8737fe2cdf 100644
--- a/frontend/src/app/render_wasm/api.cljs
+++ b/frontend/src/app/render_wasm/api.cljs
@@ -132,7 +132,6 @@
                              (aget buffer 1)
                              (aget buffer 2)
                              (aget buffer 3)
-                             image-ptr
                              image-size)
                      true))))))
 
diff --git a/render-wasm/src/main.rs b/render-wasm/src/main.rs
index 804c6f0a42..f7f082a955 100644
--- a/render-wasm/src/main.rs
+++ b/render-wasm/src/main.rs
@@ -182,35 +182,32 @@ pub extern "C" fn add_shape_fill_stops(ptr: *mut shapes::RawStopData, n_stops: u
 
     if let Some(shape) = state.current_shape() {
         let len = n_stops as usize;
-        let buffer_size = std::mem::size_of::<shapes::RawStopData>() * len;
 
         unsafe {
             let buffer = Vec::<shapes::RawStopData>::from_raw_parts(ptr, len, len);
             shape
                 .add_gradient_stops(buffer)
                 .expect("could not add gradient stops");
-            mem::free(ptr as *mut u8, buffer_size);
+            mem::free_bytes();
         }
     }
 }
 
 #[no_mangle]
-pub extern "C" fn store_image(a: u32, b: u32, c: u32, d: u32, ptr: *mut u8, size: u32) {
-    if ptr.is_null() || size == 0 {
-        panic!("Invalid data, null pointer or zero size");
-    }
+pub extern "C" fn store_image(a: u32, b: u32, c: u32, d: u32, size: u32) {
     let state = unsafe { STATE.as_mut() }.expect("got an invalid state pointer");
     let id = uuid_from_u32_quartet(a, b, c, d);
 
     unsafe {
-        let image_bytes = Vec::<u8>::from_raw_parts(ptr, size as usize, size as usize);
+        let image_bytes =
+            Vec::<u8>::from_raw_parts(mem::buffer_ptr(), size as usize, size as usize);
         match state.render_state().add_image(id, &image_bytes) {
             Err(msg) => {
                 eprintln!("{}", msg);
             }
             _ => {}
         }
-        mem::free(ptr as *mut u8, size as usize * std::mem::size_of::<u8>());
+        mem::free_bytes();
     }
 }
 
diff --git a/render-wasm/src/mem.rs b/render-wasm/src/mem.rs
index fecd40758d..a23010df20 100644
--- a/render-wasm/src/mem.rs
+++ b/render-wasm/src/mem.rs
@@ -1,17 +1,25 @@
+static mut BUFFERU8: Option<Box<Vec<u8>>> = None;
+
 #[no_mangle]
 pub extern "C" fn alloc_bytes(len: usize) -> *mut u8 {
-    // create a new mutable buffer with capacity `len`
-    let mut buf: Vec<u8> = Vec::with_capacity(len);
-    let ptr = buf.as_mut_ptr();
-    // take ownership of the memory block and ensure the its destructor is not
-    // called when the object goes out of scope at the end of the function
-    std::mem::forget(buf);
+    // TODO: Figure out how to deal with Result<T> from Emscripten
+    if unsafe { BUFFERU8.is_some() } {
+        panic!("Bytes already allocated");
+    }
+
+    let mut buffer = Box::new(Vec::<u8>::with_capacity(len));
+    let ptr = buffer.as_mut_ptr();
+
+    unsafe { BUFFERU8 = Some(buffer) };
     return ptr;
 }
 
-pub fn free(ptr: *mut u8, len: usize) {
-    unsafe {
-        let buf = Vec::<u8>::from_raw_parts(ptr, len, len);
-        std::mem::forget(buf);
-    }
+pub fn free_bytes() {
+    let buffer = unsafe { BUFFERU8.take() }.expect("uninitialized buffer");
+    std::mem::drop(buffer);
+}
+
+pub fn buffer_ptr() -> *mut u8 {
+    let buffer = unsafe { BUFFERU8.as_mut() }.expect("uninitializied buffer");
+    buffer.as_mut_ptr()
 }