WebGL2 multiview support via OVR_multiview2 (#3121)

* Add OVR_multiview2 support

* Add changelog entry

* Only use multiview on wasm32 + unknown

* Add note to Features::MULTIVIEW

CHANGELOG.md

@@ -50,6 +50,10 @@ Bottom level categories:
 #### WebGPU
 - Implement `queue_validate_write_buffer` by @jinleili in [#3098](https://github.com/gfx-rs/wgpu/pull/3098)
 
+#### GLES
+
+- Browsers that support `OVR_multiview2` now report the `MULTIVIEW` feature by @expenses in [#3121](https://github.com/gfx-rs/wgpu/pull/3121).
+
 ### Added/New Features
 
 #### General

wgpu-hal/src/gles/adapter.rs

@@ -330,6 +330,10 @@ impl super::Adapter {
             downlevel_flags.contains(wgt::DownlevelFlags::VERTEX_STORAGE)
                 && vertex_shader_storage_textures != 0,
         );
+        features.set(
+            wgt::Features::MULTIVIEW,
+            extensions.contains("OVR_multiview2"),
+        );
         let gles_bcn_exts = [
             "GL_EXT_texture_compression_s3tc_srgb",
             "GL_EXT_texture_compression_rgtc",

wgpu-hal/src/gles/device.rs

@@ -20,6 +20,7 @@ struct CompilationContext<'a> {
     layout: &'a super::PipelineLayout,
     sampler_map: &'a mut super::SamplerBindMap,
     name_binding_map: &'a mut NameBindingMap,
+    multiview: Option<std::num::NonZeroU32>,
 }
 
 impl CompilationContext<'_> {
@@ -205,7 +206,7 @@ impl super::Device {
         let pipeline_options = glsl::PipelineOptions {
             shader_stage: naga_stage,
             entry_point: stage.entry_point.to_string(),
-            multiview: None,
+            multiview: context.multiview,
         };
 
         let shader = &stage.module.naga;
@@ -269,6 +270,7 @@ impl super::Device {
         shaders: I,
         layout: &super::PipelineLayout,
         #[cfg_attr(target_arch = "wasm32", allow(unused))] label: Option<&str>,
+        multiview: Option<std::num::NonZeroU32>,
     ) -> Result<super::PipelineInner, crate::PipelineError> {
         let program = gl.create_program().unwrap();
         #[cfg(not(target_arch = "wasm32"))]
@@ -289,6 +291,7 @@ impl super::Device {
                 layout,
                 sampler_map: &mut sampler_map,
                 name_binding_map: &mut name_binding_map,
+                multiview,
             };
 
             let shader = Self::create_shader(gl, naga_stage, stage, context)?;
@@ -1032,7 +1035,7 @@ impl crate::Device<super::Api> for super::Device {
                 .as_ref()
                 .map(|fs| (naga::ShaderStage::Fragment, fs)),
         );
-        let inner = self.create_pipeline(gl, shaders, desc.layout, desc.label)?;
+        let inner = self.create_pipeline(gl, shaders, desc.layout, desc.label, desc.multiview)?;
 
         let (vertex_buffers, vertex_attributes) = {
             let mut buffers = Vec::new();
@@ -1100,7 +1103,7 @@ impl crate::Device<super::Api> for super::Device {
     ) -> Result<super::ComputePipeline, crate::PipelineError> {
         let gl = &self.shared.context.lock();
         let shaders = iter::once((naga::ShaderStage::Compute, &desc.stage));
-        let inner = self.create_pipeline(gl, shaders, desc.layout, desc.label)?;
+        let inner = self.create_pipeline(gl, shaders, desc.layout, desc.label, None)?;
 
         Ok(super::ComputePipeline { inner })
     }

wgpu-hal/src/gles/queue.rs

@@ -89,7 +89,18 @@ impl super::Queue {
             }
             super::TextureInner::DefaultRenderbuffer => panic!("Unexpected default RBO"),
             super::TextureInner::Texture { raw, target } => {
-                if is_layered_target(target) {
+                let num_layers = view.array_layers.end - view.array_layers.start;
+                if num_layers > 1 {
+                    #[cfg(all(target_arch = "wasm32", target_os = "unknown"))]
+                    gl.framebuffer_texture_multiview_ovr(
+                        fbo_target,
+                        attachment,
+                        Some(raw),
+                        view.mip_levels.start as i32,
+                        view.array_layers.start as i32,
+                        num_layers as i32,
+                    );
+                } else if is_layered_target(target) {
                     gl.framebuffer_texture_layer(
                         fbo_target,
                         attachment,

wgpu-types/src/lib.rs

@@ -586,6 +586,7 @@ bitflags::bitflags! {
         ///
         /// Supported platforms:
         /// - Vulkan
+        /// - OpenGL (web only)
         ///
         /// This is a native only feature.
         const MULTIVIEW = 1 << 37;