bevy_pbr2: Fix comments about data in cluster bindings, max lights, etc

pipelined/bevy_pbr2/src/render/light.rs

@@ -878,15 +878,16 @@ const CLUSTER_COUNT_MASK: u32 = (1 << 8) - 1;
 const POINT_LIGHT_INDEX_MASK: u32 = (1 << 8) - 1;
 
 // NOTE: With uniform buffer max binding size as 16384 bytes
-// that means we can fit say 128 point lights in one uniform
-// buffer, which means the count can be at most 128 so it
-// needs 7 bits, use 8 for convenience.
+// that means we can fit say 256 point lights in one uniform
+// buffer, which means the count can be at most 256 so it
+// needs 8 bits.
 // The array of indices can also use u8 and that means the
 // offset in to the array of indices needs to be able to address
-// 16384 values. lod2(16384) = 21 bits.
+// 16384 values. log2(16384) = 14 bits.
 // This means we can pack the offset into the upper 24 bits of a u32
 // and the count into the lower 8 bits.
-// FIXME: Probably there are endianness concerns here????!!!!!
+// NOTE: This assumes CPU and GPU endianness are the same which is true
+// for all common and tested x86/ARM CPUs and AMD/NVIDIA/Intel/Apple/etc GPUs
 fn pack_offset_and_count(offset: usize, count: usize) -> u32 {
     ((offset as u32 & CLUSTER_OFFSET_MASK) << CLUSTER_COUNT_SIZE)
         | (count as u32 & CLUSTER_COUNT_MASK)

pipelined/bevy_pbr2/src/render/mesh.rs

@@ -245,7 +245,7 @@ impl FromWorld for MeshPipeline {
                         ty: BufferBindingType::Uniform,
                         has_dynamic_offset: false,
                         // NOTE: Static size for uniform buffers. GpuPointLight has a padded
-                        // size of 128 bytes, so 16384 / 128 = 128 point lights max
+                        // size of 64 bytes, so 16384 / 64 = 256 point lights max
                         min_binding_size: BufferSize::new(16384),
                     },
                     count: None,
@@ -257,8 +257,7 @@ impl FromWorld for MeshPipeline {
                     ty: BindingType::Buffer {
                         ty: BufferBindingType::Uniform,
                         has_dynamic_offset: false,
-                        // NOTE: With 128 point lights max, indices need 7 bits. Use u8 for
-                        // convenience.
+                        // NOTE: With 256 point lights max, indices need 8 bits so use u8
                         min_binding_size: BufferSize::new(16384),
                     },
                     count: None,
@@ -270,10 +269,10 @@ impl FromWorld for MeshPipeline {
                     ty: BindingType::Buffer {
                         ty: BufferBindingType::Uniform,
                         has_dynamic_offset: false,
-                        // NOTE: The offset needs to address 16384 indices, which needs 21 bits.
-                        // The count can be at most all 128 lights so 7 bits.
+                        // NOTE: The offset needs to address 16384 indices, which needs 14 bits.
+                        // The count can be at most all 256 lights so 8 bits.
                         // Pack the offset into the upper 24 bits and the count into the
-                        // lower 8 bits for convenience.
+                        // lower 8 bits.
                         min_binding_size: BufferSize::new(16384),
                     },
                     count: None,