Fix indirect render using the wrong index

src/render/mod.rs

@@ -378,6 +378,9 @@ pub struct GpuParticleGroup {
     /// Index of the [`GpuDispatchIndirect`] struct inside the global
     /// [`EffectsMeta::dispatch_indirect_buffer`].
     pub indirect_dispatch_index: u32,
+    /// Index of the [`GpuRenderGroupIndirect`] struct inside the global
+    /// [`EffectsMeta::render_group_dispatch_buffer`].
+    pub indirect_render_index: u32,
 }
 
 /// Compute pipeline to run the `vfx_indirect` dispatch workgroup calculation
@@ -2434,6 +2437,14 @@ pub(crate) fn prepare_effects(
         let mut first_particle_group_buffer_index = None;
         let mut local_group_count = 0;
         for (group_index, range) in input.effect_slices.slices.windows(2).enumerate() {
+            let indirect_render_index = match &dispatch_buffer_indices.render_group_dispatch_indices
+            {
+                RenderGroupDispatchIndices::Allocated {
+                    first_render_group_dispatch_buffer_index,
+                    ..
+                } => first_render_group_dispatch_buffer_index.0 + group_index as u32,
+                _ => u32::MAX, // should never happen, as lazily allocated above (unless something went wrong)
+            };
             let particle_group_buffer_index =
                 effects_meta.particle_group_buffer.push(GpuParticleGroup {
                     global_group_index: total_group_count,
@@ -2448,6 +2459,7 @@ pub(crate) fn prepare_effects(
                         .first_update_group_dispatch_buffer_index
                         .0
                         + group_index as u32,
+                    indirect_render_index,
                 });
             if group_index == 0 {
                 first_particle_group_buffer_index = Some(particle_group_buffer_index as u32);

src/render/vfx_common.wgsl

@@ -71,6 +71,9 @@ struct ParticleGroup {
     /// Index of the [`GpuDispatchIndirect`] struct inside the global
     /// [`EffectsMeta::dispatch_indirect_buffer`].
     indirect_dispatch_index: u32,
+    /// Index of the [`GpuRenderGroupIndirect`] struct inside the global
+    /// [`EffectsMeta::render_group_dispatch_buffer`].
+    indirect_render_index: u32,
     {{PARTICLE_GROUP_PADDING}}
 }
 

src/render/vfx_indirect.wgsl

@@ -43,15 +43,10 @@ fn main(@builtin(global_invocation_id) global_invocation_id: vec3<u32>) {
     let group_index_in_effect = group_buffer[index].index_in_effect;
     let is_first_group = group_index_in_effect == 0u;
 
-    // Calculate the base offset (in number of u32 items) into the render indirect and
-    // dispatch indirect arrays.
-    let rgi_base = RENDER_GROUP_INDIRECT_STRIDE * group_index;
-
-    let indirect_dispatch_index = group_buffer[index].indirect_dispatch_index;
-    let di_base = DISPATCH_INDIRECT_STRIDE * indirect_dispatch_index;
-
     // Clear the rendering instance count, which will be upgraded by the update pass
     // with the particles actually alive at the end of their update (after aged).
+    let indirect_render_index = group_buffer[index].indirect_render_index;
+    let rgi_base = RENDER_GROUP_INDIRECT_STRIDE * indirect_render_index;
     render_group_indirect_buffer[rgi_base + RGI_OFFSET_INSTANCE_COUNT] = 0u;
 
     let alive_count = render_group_indirect_buffer[rgi_base + RGI_OFFSET_ALIVE_COUNT];
@@ -60,6 +55,8 @@ fn main(@builtin(global_invocation_id) global_invocation_id: vec3<u32>) {
     // Calculate the number of thread groups to dispatch for the update
     // pass, which is the number of alive particles rounded up to 64
     // (workgroup_size).
+    let indirect_dispatch_index = group_buffer[index].indirect_dispatch_index;
+    let di_base = DISPATCH_INDIRECT_STRIDE * indirect_dispatch_index;
     dispatch_indirect_buffer[di_base + DI_OFFSET_X] = (alive_count + 63u) >> 6u;
 
     // Update max_update from current value of alive_count, so that the