Added new UNRESTRICTED_INDEX_BUFFER downlevel flag. (#3157)

Co-authored-by: Connor Fitzgerald <connorwadefitzgerald@gmail.com>

CHANGELOG.md

@@ -47,6 +47,7 @@ Bottom level categories:
 - Convert all `Default` Implementations on Enums to `derive(Default)`
 - Implement `Default` for `CompositeAlphaMode`
 - Improve compute shader validation error message. By @haraldreingruber in [#3139](https://github.com/gfx-rs/wgpu/pull/3139)
+- New downlevel feature `UNRESTRICTED_INDEX_BUFFER` to indicate support for using `INDEX` together with other non-copy/map usages (unsupported on WebGL). By @Wumpf in [#3157](https://github.com/gfx-rs/wgpu/pull/3157)
 
 #### WebGPU
 - Implement `queue_validate_write_buffer` by @jinleili in [#3098](https://github.com/gfx-rs/wgpu/pull/3098)

wgpu-core/src/command/transfer.rs

@@ -544,10 +544,13 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
         let hub = A::hub(self);
         let mut token = Token::root();
 
+        let (device_guard, mut token) = hub.devices.read(&mut token);
         let (mut cmd_buf_guard, mut token) = hub.command_buffers.write(&mut token);
         let cmd_buf = CommandBuffer::get_encoder_mut(&mut *cmd_buf_guard, command_encoder_id)?;
         let (buffer_guard, _) = hub.buffers.read(&mut token);
 
+        let device = &device_guard[cmd_buf.device_id.value];
+
         #[cfg(feature = "trace")]
         if let Some(ref mut list) = cmd_buf.commands {
             list.push(TraceCommand::CopyBufferToBuffer {
@@ -597,6 +600,26 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
         if destination_offset % wgt::COPY_BUFFER_ALIGNMENT != 0 {
             return Err(TransferError::UnalignedBufferOffset(destination_offset).into());
         }
+        if !device
+            .downlevel
+            .flags
+            .contains(wgt::DownlevelFlags::UNRESTRICTED_INDEX_BUFFER)
+            && (src_buffer.usage.contains(wgt::BufferUsages::INDEX)
+                || dst_buffer.usage.contains(wgt::BufferUsages::INDEX))
+        {
+            let forbidden_usages = wgt::BufferUsages::VERTEX
+                | wgt::BufferUsages::UNIFORM
+                | wgt::BufferUsages::INDIRECT
+                | wgt::BufferUsages::STORAGE;
+            if src_buffer.usage.intersects(forbidden_usages)
+                || dst_buffer.usage.intersects(forbidden_usages)
+            {
+                return Err(TransferError::MissingDownlevelFlags(MissingDownlevelFlags(
+                    wgt::DownlevelFlags::UNRESTRICTED_INDEX_BUFFER,
+                ))
+                .into());
+            }
+        }
 
         let source_end_offset = source_offset + size;
         let destination_end_offset = destination_offset + size;

wgpu-core/src/device/mod.rs

@@ -590,6 +590,17 @@ impl<A: HalApi> Device<A> {
             });
         }
 
+        if desc.usage.contains(wgt::BufferUsages::INDEX)
+            && desc.usage.contains(
+                wgt::BufferUsages::VERTEX
+                    | wgt::BufferUsages::UNIFORM
+                    | wgt::BufferUsages::INDIRECT
+                    | wgt::BufferUsages::STORAGE,
+            )
+        {
+            self.require_downlevel_flags(wgt::DownlevelFlags::UNRESTRICTED_INDEX_BUFFER)?;
+        }
+
         let mut usage = conv::map_buffer_usage(desc.usage);
 
         if desc.usage.is_empty() {

wgpu-core/src/resource.rs

@@ -1,5 +1,5 @@
 use crate::{
-    device::{DeviceError, HostMap, MissingFeatures},
+    device::{DeviceError, HostMap, MissingDownlevelFlags, MissingFeatures},
     hub::{Global, GlobalIdentityHandlerFactory, HalApi, Resource, Token},
     id::{AdapterId, DeviceId, SurfaceId, TextureId, Valid},
     init_tracker::{BufferInitTracker, TextureInitTracker},
@@ -248,6 +248,8 @@ pub enum CreateBufferError {
     UsageMismatch(wgt::BufferUsages),
     #[error("Buffer size {requested} is greater than the maximum buffer size ({maximum})")]
     MaxBufferSize { requested: u64, maximum: u64 },
+    #[error(transparent)]
+    MissingDownlevelFlags(#[from] MissingDownlevelFlags),
 }
 
 impl<A: hal::Api> Resource for Buffer<A> {

wgpu-hal/src/dx11/adapter.rs

@@ -91,8 +91,9 @@ impl super::Adapter {
             | wgt::Features::CLEAR_TEXTURE
             | wgt::Features::TEXTURE_FORMAT_16BIT_NORM
             | wgt::Features::ADDRESS_MODE_CLAMP_TO_ZERO;
-        let mut downlevel =
-            wgt::DownlevelFlags::BASE_VERTEX | wgt::DownlevelFlags::READ_ONLY_DEPTH_STENCIL;
+        let mut downlevel = wgt::DownlevelFlags::BASE_VERTEX
+            | wgt::DownlevelFlags::READ_ONLY_DEPTH_STENCIL
+            | wgt::DownlevelFlags::UNRESTRICTED_INDEX_BUFFER;
 
         // Features from queries
         downlevel.set(

wgpu-hal/src/gles/adapter.rs

@@ -312,6 +312,11 @@ impl super::Adapter {
             wgt::DownlevelFlags::BUFFER_BINDINGS_NOT_16_BYTE_ALIGNED,
             !(cfg!(target_arch = "wasm32") || is_angle),
         );
+        // see https://registry.khronos.org/webgl/specs/latest/2.0/#BUFFER_OBJECT_BINDING
+        downlevel_flags.set(
+            wgt::DownlevelFlags::UNRESTRICTED_INDEX_BUFFER,
+            !cfg!(target_arch = "wasm32"),
+        );
 
         let mut features = wgt::Features::empty()
             | wgt::Features::TEXTURE_ADAPTER_SPECIFIC_FORMAT_FEATURES

wgpu-types/src/lib.rs

@@ -1056,7 +1056,7 @@ bitflags::bitflags! {
 
         /// Supports samplers with anisotropic filtering. Note this isn't actually required by
         /// WebGPU, the implementation is allowed to completely ignore aniso clamp. This flag is
-        /// here for native backends so they can comunicate to the user of aniso is enabled.
+        /// here for native backends so they can communicate to the user of aniso is enabled.
         ///
         /// All backends and all devices support anisotropic filtering.
         const ANISOTROPIC_FILTERING = 1 << 10;
@@ -1080,6 +1080,13 @@ bitflags::bitflags! {
         ///
         /// WebGL doesn't support this.
         const BUFFER_BINDINGS_NOT_16_BYTE_ALIGNED = 1 << 15;
+
+        /// Supports buffers to combine [`BufferUsages::INDEX`] with usages other than [`BufferUsages::COPY_DST`] and [`BufferUsages::COPY_SRC`].
+        /// Furthermore, in absence of this feature it is not allowed to copy index buffers from/to buffers with a set of usage flags containing
+         /// [`BufferUsages::VERTEX`]/[`BufferUsages::UNIFORM`]/[`BufferUsages::STORAGE`] or [`BufferUsages::INDIRECT`].
+        ///
+        /// WebGL doesn't support this.
+        const UNRESTRICTED_INDEX_BUFFER = 1 << 16;
     }
 }