From b70c2724b2288231b727eb37e7b3333aed9e69c7 Mon Sep 17 00:00:00 2001
From: daslastic <daslastic@gmail.com>
Date: Thu, 8 Feb 2024 02:38:48 -0500
Subject: [PATCH] allow positional buffer updates

---
 src/graphics.rs       | 1 +
 src/graphics/gl.rs    | 9 ++++++---
 src/graphics/metal.rs | 8 ++++++--
 3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/src/graphics.rs b/src/graphics.rs
index b888c395..a958d785 100644
--- a/src/graphics.rs
+++ b/src/graphics.rs
@@ -1201,6 +1201,7 @@ pub trait RenderingBackend {
     fn new_buffer(&mut self, type_: BufferType, usage: BufferUsage, data: BufferSource)
         -> BufferId;
     fn buffer_update(&mut self, buffer: BufferId, data: BufferSource);
+    fn buffer_update_at(&mut self, buffer: BufferId, data: BufferSource, at: usize);
 
     /// Size of buffer in bytes.
     /// For 1 element, u16 buffer this will return 2.
diff --git a/src/graphics/gl.rs b/src/graphics/gl.rs
index ab5a445f..5f49d035 100644
--- a/src/graphics/gl.rs
+++ b/src/graphics/gl.rs
@@ -1181,7 +1181,7 @@ impl RenderingBackend for GlContext {
         BufferId(self.buffers.len() - 1)
     }
 
-    fn buffer_update(&mut self, buffer: BufferId, data: BufferSource) {
+    fn buffer_update_at(&mut self, buffer: BufferId, data: BufferSource, at: usize) {
         let data = match data {
             BufferSource::Slice(data) => data,
             _ => panic!("buffer_update expects BufferSource::slice"),
@@ -1201,11 +1201,14 @@ impl RenderingBackend for GlContext {
         let gl_target = gl_buffer_target(&buffer.buffer_type);
         self.cache.store_buffer_binding(gl_target);
         self.cache
-            .bind_buffer(gl_target, buffer.gl_buf, buffer.index_type);
-        unsafe { glBufferSubData(gl_target, 0, size as _, data.ptr as _) };
+            .bind_buffer(gl_target, buffer.gl_buf, buffer.index_type); unsafe { glBufferSubData(gl_target, (at * size) as i64, size as _, data.ptr as _) };
         self.cache.restore_buffer_binding(gl_target);
     }
 
+    fn buffer_update(&mut self, buffer: BufferId, data: BufferSource) {
+        self.buffer_update_at(buffer, data, 0);
+    }
+
     /// Size of buffer in bytes
     fn buffer_size(&mut self, buffer: BufferId) -> usize {
         self.buffers[buffer.0].size
diff --git a/src/graphics/metal.rs b/src/graphics/metal.rs
index 98ad801b..c72dab1d 100644
--- a/src/graphics/metal.rs
+++ b/src/graphics/metal.rs
@@ -626,7 +626,7 @@ impl RenderingBackend for MetalContext {
         BufferId(self.buffers.len() - 1)
     }
 
-    fn buffer_update(&mut self, buffer: BufferId, data: BufferSource) {
+    fn buffer_update_at(&mut self, buffer: BufferId, data: BufferSource, at: usize) {
         let data = match data {
             BufferSource::Slice(data) => data,
             _ => panic!("buffer_update expects BufferSource::slice"),
@@ -639,11 +639,15 @@ impl RenderingBackend for MetalContext {
             std::ptr::copy(data.ptr, dest, data.size);
 
             #[cfg(target_os = "macos")]
-            msg_send_![buffer.raw[buffer.next_value], didModifyRange:NSRange::new(0, data.size as u64)];
+            msg_send_![buffer.raw[buffer.next_value], didModifyRange:NSRange::new((at * data.size) as u64, data.size as u64)];
         }
         buffer.value = buffer.next_value;
     }
 
+    fn buffer_update(&mut self, buffer: BufferId, data: BufferSource) {
+        self.buffer_update_at(buffer, data, 0);
+    }
+
     fn new_shader(
         &mut self,
         shader: ShaderSource,