Merge #754

754: Implement MultiDrawIndirect Extensions r=kvark a=cwfitzgerald

**Connections**

Closes #742.

**Description**

These extensions, especially when combined with binding indexing, allow the creation of extremely cpu-efficient gpu powered pipelines.

Adds two extensions allowing various types of multi-draw-indirect
- MULTI_DRAW_INDIRECT (giving `multi_draw_indirect` and `multi_draw_indexed_indirect`)
- MULTI_DRAW_INDIRECT_COUNT (giving `multi_draw_indirect_count` and `multi_draw_indexed_indirect_count`)

This adds what I believe to be an extra restriction on the `*count` family of functions when compared to the underlying api. The buffer _must_ be large enough to draw `max_count` draws, even if that many draws are never drawn. This makes these operations no more unsafe than indirect would be, which is currently safe.

I did not implement these for renderbundles, but there's no reason they couldn't work, so those branches are marked with `unimplemented` as opposed to `unreachable`.

Additional Changes:
- Added some validation to the normal `draw_*_indirect` functions to prevent buffer overruns.
- The DX12 gfx-hal backend requires the strides to _always_ be non-zero, so I modified the normal indirect draws to use explicit strides.
- Made device limits and features `pub(crate)` as they need to be checked in random places in the code.

**Testing**

The change was tested using a modified version of wgpu-rs's texture-array example using a variety of permutations. I have not been able to test regular MULTI_DRAW_INDIRECT on mac, but I see no reason why that wouldn't work.

gfx-rs/wgpu-rs#414

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

wgpu-core/Cargo.toml

@@ -28,7 +28,7 @@ bitflags = "1.0"
 copyless = "0.1"
 fxhash = "0.2"
 log = "0.4"
-hal = { package = "gfx-hal", version = "0.5.2" }
+hal = { package = "gfx-hal", version = "0.5.3" }
 gfx-backend-empty = "0.5"
 parking_lot = "0.10"
 raw-window-handle = { version = "0.3", optional = true }
@@ -60,15 +60,15 @@ version = "0.5"
 
 [target.'cfg(any(target_os = "ios", target_os = "macos"))'.dependencies]
 gfx-backend-metal = { version = "0.5.4" }
-gfx-backend-vulkan = { version = "0.5.6", optional = true }
+gfx-backend-vulkan = { version = "0.5.9", optional = true }
 
 [target.'cfg(all(unix, not(target_os = "ios"), not(target_os = "macos")))'.dependencies]
-gfx-backend-vulkan = { version = "0.5.6" }
+gfx-backend-vulkan = { version = "0.5.9" }
 
 [target.'cfg(windows)'.dependencies]
-gfx-backend-dx12 = { version = "0.5.6" }
+gfx-backend-dx12 = { version = "0.5.8" }
 gfx-backend-dx11 = { version = "0.5" }
-gfx-backend-vulkan = { version = "0.5.8" }
+gfx-backend-vulkan = { version = "0.5.9" }
 
 [target.'cfg(any(target_os = "linux", target_os = "macos", target_os = "windows", target_os = "dragonfly", target_os = "freebsd"))'.dependencies]
 battery = { version = "0.7", optional = true }

wgpu-core/src/command/bundle.rs

@@ -203,14 +203,26 @@ impl RenderBundle {
                         first_instance..first_instance + instance_count,
                     );
                 }
-                RenderCommand::DrawIndirect { buffer_id, offset } => {
+                RenderCommand::MultiDrawIndirect {
+                    buffer_id,
+                    offset,
+                    count: None,
+                    indexed: false,
+                } => {
                     let buffer = &buffer_guard[buffer_id];
                     comb.draw_indirect(&buffer.raw, offset, 1, 0);
                 }
-                RenderCommand::DrawIndexedIndirect { buffer_id, offset } => {
+                RenderCommand::MultiDrawIndirect {
+                    buffer_id,
+                    offset,
+                    count: None,
+                    indexed: true,
+                } => {
                     let buffer = &buffer_guard[buffer_id];
                     comb.draw_indexed_indirect(&buffer.raw, offset, 1, 0);
                 }
+                RenderCommand::MultiDrawIndirect { .. }
+                | RenderCommand::MultiDrawIndirectCount { .. } => unimplemented!(),
                 RenderCommand::PushDebugGroup { color: _, len: _ } => unimplemented!(),
                 RenderCommand::InsertDebugMarker { color: _, len: _ } => unimplemented!(),
                 RenderCommand::PopDebugGroup => unimplemented!(),
@@ -652,9 +664,11 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
                         commands.extend(state.flush_binds());
                         commands.push(command);
                     }
-                    RenderCommand::DrawIndirect {
+                    RenderCommand::MultiDrawIndirect {
                         buffer_id,
                         offset: _,
+                        count: None,
+                        indexed: false,
                     } => {
                         let buffer = state
                             .trackers
@@ -671,9 +685,11 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
                         commands.extend(state.flush_binds());
                         commands.push(command);
                     }
-                    RenderCommand::DrawIndexedIndirect {
+                    RenderCommand::MultiDrawIndirect {
                         buffer_id,
                         offset: _,
+                        count: None,
+                        indexed: true,
                     } => {
                         let buffer = state
                             .trackers
@@ -691,6 +707,8 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
                         commands.extend(state.flush_binds());
                         commands.push(command);
                     }
+                    RenderCommand::MultiDrawIndirect { .. }
+                    | RenderCommand::MultiDrawIndirectCount { .. } => unimplemented!(),
                     RenderCommand::PushDebugGroup { color: _, len: _ } => unimplemented!(),
                     RenderCommand::InsertDebugMarker { color: _, len: _ } => unimplemented!(),
                     RenderCommand::PopDebugGroup => unimplemented!(),
@@ -872,10 +890,12 @@ pub mod bundle_ffi {
         offset: BufferAddress,
     ) {
         span!(_guard, DEBUG, "RenderBundle::draw_indirect");
-        bundle
-            .base
-            .commands
-            .push(RenderCommand::DrawIndirect { buffer_id, offset });
+        bundle.base.commands.push(RenderCommand::MultiDrawIndirect {
+            buffer_id,
+            offset,
+            count: None,
+            indexed: false,
+        });
     }
 
     #[no_mangle]
@@ -885,10 +905,12 @@ pub mod bundle_ffi {
         offset: BufferAddress,
     ) {
         span!(_guard, DEBUG, "RenderBundle::draw_indexed_indirect");
-        bundle
-            .base
-            .commands
-            .push(RenderCommand::DrawIndexedIndirect { buffer_id, offset });
+        bundle.base.commands.push(RenderCommand::MultiDrawIndirect {
+            buffer_id,
+            offset,
+            count: None,
+            indexed: true,
+        });
     }
 
     #[no_mangle]