feat(engine): add offset options to renderer::Command::DrawMesh

2 files changed, 46 insertions, 11 deletions

diff --git a/engine/src/renderer.rs b/engine/src/renderer.rs
index 52764db..b52e6b9 100644
--- a/engine/src/renderer.rs
+++ b/engine/src/renderer.rs
@@ -191,10 +191,40 @@ pub enum Command
         mesh: Mesh,
         usage: MeshUsage,
     },
-    DrawMesh(ObjectId),
+    DrawMesh(ObjectId, DrawMeshOptions),
     UpdateDrawProperties(DrawProperties, DrawPropertiesUpdateFlags),
 }
 
+builder! {
+    #[builder(name = DrawMeshOptionsBuilder, derives = (Debug, Default, Clone))]
+    #[derive(Debug, Default, Clone)]
+    #[non_exhaustive]
+    pub struct DrawMeshOptions {
+        pub element_offset: u32,
+        pub vertex_offset: u32,
+
+        #[builder(skip_generate_fn)]
+        pub element_cnt: Option<u32>,
+    }
+}
+
+impl DrawMeshOptions
+{
+    pub fn builder() -> DrawMeshOptionsBuilder
+    {
+        DrawMeshOptionsBuilder::default()
+    }
+}
+
+impl DrawMeshOptionsBuilder
+{
+    pub fn element_cnt(mut self, element_cnt: u32) -> Self
+    {
+        self.element_cnt = Some(element_cnt);
+        self
+    }
+}
+
 bitflags! {
     #[derive(Debug)]
     pub struct BufferClearMask: u8 {
@@ -531,9 +561,10 @@ pub fn add_main_render_passes(
                     });
                 }
 
-                render_pass
-                    .commands
-                    .push(Command::DrawMesh(ObjectId::Asset(mesh_asset.id())));
+                render_pass.commands.push(Command::DrawMesh(
+                    ObjectId::Asset(mesh_asset.id()),
+                    DrawMeshOptions::default(),
+                ));
 
                 if let Some(draw_flags) = draw_flags.as_deref()
                     && draw_flags.polygon_mode_config != PolygonModeConfig::default()
diff --git a/engine/src/renderer/opengl.rs b/engine/src/renderer/opengl.rs
index b434cd8..81cbdc2 100644
--- a/engine/src/renderer/opengl.rs
+++ b/engine/src/renderer/opengl.rs
@@ -93,6 +93,7 @@ use crate::renderer::{
     Command as RendererCommand,
     CommandQueue as RendererCommandQueue,
     CtxUsedByWindow as RendererCtxUsedByWindow,
+    DrawMeshOptions,
     DrawPropertiesUpdateFlags,
     GraphicsProperties,
     PRE_RENDER_PHASE,
@@ -1089,7 +1090,7 @@ fn handle_commands(
                         tracing::error!("Failed to update mesh: {err}");
                     }
                 }
-                RendererCommand::DrawMesh(mesh_object_id) => {
+                RendererCommand::DrawMesh(mesh_object_id, draw_mesh_opts) => {
                     let Some(curr_gl_ctx) = &opt_curr_gl_ctx else {
                         tracing::error!("No GL context is current");
                         continue;
@@ -1145,7 +1146,9 @@ fn handle_commands(
                         continue;
                     }
 
-                    if let Err(err) = draw_mesh(&curr_gl_ctx, graphics_mesh) {
+                    if let Err(err) =
+                        draw_mesh(&curr_gl_ctx, graphics_mesh, &draw_mesh_opts)
+                    {
                         tracing::error!("Failed to draw mesh: {err}");
                     };
                 }
@@ -1330,6 +1333,7 @@ fn set_viewport(
 fn draw_mesh(
     current_context: &CurrentContextWithFns<'_>,
     graphics_mesh: &GraphicsMesh,
+    opts: &DrawMeshOptions,
 ) -> Result<(), GlDrawError>
 {
     graphics_mesh.vertex_arr.bind(current_context);
@@ -1339,17 +1343,17 @@ fn draw_mesh(
             current_context,
             opengl_bindings::vertex_array::DrawElementsOptions {
                 primitive_kind: PrimitiveKind::Triangles,
-                element_offset: 0,
-                element_cnt: graphics_mesh.element_cnt,
-                vertex_offset: 0,
+                element_offset: opts.element_offset,
+                element_cnt: opts.element_cnt.unwrap_or(graphics_mesh.element_cnt),
+                vertex_offset: opts.vertex_offset,
             },
         )?;
     } else {
         VertexArray::draw_arrays(
             current_context,
             PrimitiveKind::Triangles,
-            0,
-            graphics_mesh.element_cnt,
+            opts.vertex_offset,
+            opts.element_cnt.unwrap_or(graphics_mesh.element_cnt),
         )?;
     }