Merge #690

690: Implement Anisotropic Filtering Extension and Expose Extension Interface r=kvark a=cwfitzgerald

**Connections**

Resolves #568.

**Description**

This PR solves two tightly related problems:
 - Adds the ability to create a sampler with anisotropic filtering
 - Adds the webgpu interface for getting the limits/extensions on adapters and devies.

**Testing**

I have tested this against my codebase which uses it. Adding an example in wgpu-rs on how to use extensions/limits would be good, especially as we have native/webgpu extensions, but can come as a future enhancement, once we feel the extension situation has stabilized a bit.

**TODO**

- [x] Allow wgpu-rs to call limit/extension interface (gfx-rs/wgpu-rs#338)
- [ ] Determine how wgpu-native is going to adopt this functionality.
- [ ] After discussing #691, what changes need to be made. 

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

wgpu-core/src/conv.rs

@@ -429,7 +429,7 @@ fn checked_u32_as_u16(value: u32) -> u16 {
     value as u16
 }
 
-fn is_power_of_two(val: u32) -> bool {
+pub fn is_power_of_two(val: u32) -> bool {
     val != 0 && (val & (val - 1)) == 0
 }
 

wgpu-core/src/device/mod.rs

@@ -55,6 +55,7 @@ fn own_label(label: &Label) -> String {
 pub const MAX_COLOR_TARGETS: usize = 4;
 pub const MAX_MIP_LEVELS: usize = 16;
 pub const MAX_VERTEX_BUFFERS: usize = 16;
+pub const MAX_ANISOTROPY: u8 = 16;
 
 pub fn all_buffer_stages() -> hal::pso::PipelineStage {
     use hal::pso::PipelineStage as Ps;
@@ -541,6 +542,24 @@ impl<B: hal::Backend> Device<B> {
 }
 
 impl<G: GlobalIdentityHandlerFactory> Global<G> {
+    pub fn device_extensions<B: GfxBackend>(&self, device_id: id::DeviceId) -> wgt::Extensions {
+        let hub = B::hub(self);
+        let mut token = Token::root();
+        let (device_guard, _) = hub.devices.read(&mut token);
+        let device = &device_guard[device_id];
+
+        device.extensions.clone()
+    }
+
+    pub fn device_limits<B: GfxBackend>(&self, device_id: id::DeviceId) -> wgt::Limits {
+        let hub = B::hub(self);
+        let mut token = Token::root();
+        let (device_guard, _) = hub.devices.read(&mut token);
+        let device = &device_guard[device_id];
+
+        device.limits.clone()
+    }
+
     pub fn device_create_buffer<B: GfxBackend>(
         &self,
         device_id: id::DeviceId,
@@ -977,6 +996,19 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
         let (device_guard, mut token) = hub.devices.read(&mut token);
         let device = &device_guard[device_id];
 
+        if desc.anisotropy_clamp > 1 {
+            assert!(
+                device.extensions.anisotropic_filtering,
+                "Anisotropic clamp may only be used when the anisotropic filtering extension is enabled"
+            );
+            let valid_clamp = desc.anisotropy_clamp <= MAX_ANISOTROPY
+                && conv::is_power_of_two(desc.anisotropy_clamp as u32);
+            assert!(
+                valid_clamp,
+                "Anisotropic clamp must be one of the values: 0, 1, 2, 4, 8, or 16"
+            );
+        }
+
         let info = hal::image::SamplerDesc {
             min_filter: conv::map_filter(desc.min_filter),
             mag_filter: conv::map_filter(desc.mag_filter),
@@ -991,7 +1023,11 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
             comparison: conv::map_compare_function(desc.compare),
             border: hal::image::PackedColor(0),
             normalized: true,
-            anisotropy_clamp: None, //TODO
+            anisotropy_clamp: if desc.anisotropy_clamp > 1 {
+                Some(desc.anisotropy_clamp)
+            } else {
+                None
+            },
         };
 
         let sampler = resource::Sampler {

wgpu-core/src/instance.rs

@@ -7,7 +7,7 @@ use crate::{
     device::Device,
     hub::{GfxBackend, Global, GlobalIdentityHandlerFactory, Input, Token},
     id::{AdapterId, DeviceId, SurfaceId},
-    power, LifeGuard, Stored,
+    power, LifeGuard, Stored, MAX_BIND_GROUPS,
 };
 
 use wgt::{Backend, BackendBit, DeviceDescriptor, PowerPreference, BIND_BUFFER_ALIGNMENT};
@@ -527,6 +527,32 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
         AdapterInfo::from_gfx(adapter.raw.info.clone(), adapter_id.backend())
     }
 
+    pub fn adapter_extensions<B: GfxBackend>(&self, adapter_id: AdapterId) -> wgt::Extensions {
+        let hub = B::hub(self);
+        let mut token = Token::root();
+        let (adapter_guard, _) = hub.adapters.read(&mut token);
+        let adapter = &adapter_guard[adapter_id];
+
+        let features = adapter.raw.physical_device.features();
+
+        wgt::Extensions {
+            anisotropic_filtering: features.contains(hal::Features::SAMPLER_ANISOTROPY),
+        }
+    }
+
+    pub fn adapter_limits<B: GfxBackend>(&self, adapter_id: AdapterId) -> wgt::Limits {
+        let hub = B::hub(self);
+        let mut token = Token::root();
+        let (adapter_guard, _) = hub.adapters.read(&mut token);
+        let adapter = &adapter_guard[adapter_id];
+
+        let limits = adapter.raw.physical_device.limits();
+
+        wgt::Limits {
+            max_bind_groups: (limits.max_bound_descriptor_sets as u32).min(MAX_BIND_GROUPS as u32),
+        }
+    }
+
     pub fn adapter_destroy<B: GfxBackend>(&self, adapter_id: AdapterId) {
         let hub = B::hub(self);
         let mut token = Token::root();
@@ -560,17 +586,30 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
             let (adapter_guard, _) = hub.adapters.read(&mut token);
             let adapter = &adapter_guard[adapter_id];
             let phd = &adapter.raw.physical_device;
+
+            let available_features = adapter.raw.physical_device.features();
+
+            // Check features that are always needed
             let wishful_features = hal::Features::VERTEX_STORES_AND_ATOMICS
                 | hal::Features::FRAGMENT_STORES_AND_ATOMICS
                 | hal::Features::NDC_Y_UP;
-            let enabled_features = adapter.raw.physical_device.features() & wishful_features;
+            let mut enabled_features = available_features & wishful_features;
             if enabled_features != wishful_features {
                 log::warn!(
                     "Missing features: {:?}",
                     wishful_features - enabled_features
                 );
             }
 
+            // Check features needed by extensions
+            if desc.extensions.anisotropic_filtering {
+                assert!(
+                    available_features.contains(hal::Features::SAMPLER_ANISOTROPY),
+                    "Missing feature SAMPLER_ANISOTROPY for anisotropic filtering extension"
+                );
+                enabled_features |= hal::Features::SAMPLER_ANISOTROPY;
+            }
+
             let family = adapter
                 .raw
                 .queue_families

wgpu-types/src/lib.rs

@@ -88,6 +88,10 @@ impl From<Backend> for BackendBit {
 #[cfg_attr(feature = "trace", derive(Serialize))]
 #[cfg_attr(feature = "replay", derive(Deserialize))]
 pub struct Extensions {
+    /// This is a native only extension. Support is planned to be added to webgpu,
+    /// but it is not yet implemented.
+    ///
+    /// https://github.com/gpuweb/gpuweb/issues/696
     pub anisotropic_filtering: bool,
 }
 
@@ -926,6 +930,11 @@ pub struct SamplerDescriptor<L> {
     pub lod_min_clamp: f32,
     pub lod_max_clamp: f32,
     pub compare: CompareFunction,
+    /// Anisotropic filtering extension must be enabled if this value is
+    /// anything other than 0 and 1.
+    ///
+    /// Valid values are 0, 1, 2, 4, 8, and 16.
+    pub anisotropy_clamp: u8,
 }
 
 impl<L> SamplerDescriptor<L> {
@@ -941,6 +950,7 @@ impl<L> SamplerDescriptor<L> {
             lod_min_clamp: self.lod_min_clamp,
             lod_max_clamp: self.lod_max_clamp,
             compare: self.compare,
+            anisotropy_clamp: self.anisotropy_clamp,
         }
     }
 }