[WebGL] Allow creating a texture from an external web_sys::WebGlFramebuffer and writing to it (#2609)

wgpu-hal/src/gles/command.rs

@@ -452,6 +452,20 @@ impl crate::CommandEncoder<super::Api> for super::CommandEncoder {
             self.state.has_pass_label = true;
         }
 
+        let rendering_to_external_framebuffer = desc
+            .color_attachments
+            .iter()
+            .filter_map(|at| at.as_ref())
+            .any(|at| match at.target.view.inner {
+                #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
+                super::TextureInner::ExternalFramebuffer { .. } => true,
+                _ => false,
+            });
+
+        if rendering_to_external_framebuffer && desc.color_attachments.len() != 1 {
+            panic!("Multiple render attachments with external framebuffers are not supported.");
+        }
+
         match desc
             .color_attachments
             .first()
@@ -514,10 +528,12 @@ impl crate::CommandEncoder<super::Api> for super::CommandEncoder {
                     }
                 }
 
-                // set the draw buffers and states
-                self.cmd_buffer
-                    .commands
-                    .push(C::SetDrawColorBuffers(desc.color_attachments.len() as u8));
+                if !rendering_to_external_framebuffer {
+                    // set the draw buffers and states
+                    self.cmd_buffer
+                        .commands
+                        .push(C::SetDrawColorBuffers(desc.color_attachments.len() as u8));
+                }
             }
         }
 

wgpu-hal/src/gles/device.rs

@@ -813,6 +813,8 @@ impl crate::Device<super::Api> for super::Device {
                 super::TextureInner::Texture { raw, .. } => {
                     unsafe { gl.delete_texture(raw) };
                 }
+                #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
+                super::TextureInner::ExternalFramebuffer { .. } => {}
             }
         }
 

wgpu-hal/src/gles/mod.rs

@@ -187,10 +187,10 @@ impl Default for VertexAttribKind {
 }
 
 #[derive(Clone, Debug)]
-struct TextureFormatDesc {
-    internal: u32,
-    external: u32,
-    data_type: u32,
+pub struct TextureFormatDesc {
+    pub internal: u32,
+    pub external: u32,
+    pub data_type: u32,
 }
 
 struct AdapterShared {
@@ -249,7 +249,7 @@ unsafe impl Sync for Buffer {}
 unsafe impl Send for Buffer {}
 
 #[derive(Clone, Debug)]
-enum TextureInner {
+pub enum TextureInner {
     Renderbuffer {
         raw: glow::Renderbuffer,
     },
@@ -258,8 +258,18 @@ enum TextureInner {
         raw: glow::Texture,
         target: BindTarget,
     },
+    #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
+    ExternalFramebuffer {
+        inner: web_sys::WebGlFramebuffer,
+    },
 }
 
+// SAFE: WASM doesn't have threads
+#[cfg(target_arch = "wasm32")]
+unsafe impl Send for TextureInner {}
+#[cfg(target_arch = "wasm32")]
+unsafe impl Sync for TextureInner {}
+
 impl TextureInner {
     fn as_native(&self) -> (glow::Texture, BindTarget) {
         match *self {
@@ -267,21 +277,23 @@ impl TextureInner {
                 panic!("Unexpected renderbuffer");
             }
             Self::Texture { raw, target } => (raw, target),
+            #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
+            Self::ExternalFramebuffer { .. } => panic!("Unexpected external framebuffer"),
         }
     }
 }
 
 #[derive(Debug)]
 pub struct Texture {
-    inner: TextureInner,
-    drop_guard: Option<crate::DropGuard>,
-    mip_level_count: u32,
-    array_layer_count: u32,
-    format: wgt::TextureFormat,
+    pub inner: TextureInner,
+    pub drop_guard: Option<crate::DropGuard>,
+    pub mip_level_count: u32,
+    pub array_layer_count: u32,
+    pub format: wgt::TextureFormat,
     #[allow(unused)]
-    format_desc: TextureFormatDesc,
-    copy_size: CopyExtent,
-    is_cubemap: bool,
+    pub format_desc: TextureFormatDesc,
+    pub copy_size: CopyExtent,
+    pub is_cubemap: bool,
 }
 
 impl Texture {

wgpu-hal/src/gles/queue.rs

@@ -143,6 +143,10 @@ impl super::Queue {
                     };
                 }
             }
+            #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
+            super::TextureInner::ExternalFramebuffer { ref inner } => unsafe {
+                gl.bind_external_framebuffer(glow::FRAMEBUFFER, inner);
+            },
         }
     }
 

wgpu-hal/src/lib.rs

@@ -63,17 +63,23 @@ compile_error!("Metal API enabled on non-Apple OS. If your project is not using
 #[cfg(all(feature = "dx12", not(windows)))]
 compile_error!("DX12 API enabled on non-Windows OS. If your project is not using resolver=\"2\" in Cargo.toml, it should.");
 
+/// DirectX11 API internals.
 #[cfg(all(feature = "dx11", windows))]
-mod dx11;
+pub mod dx11;
+/// DirectX12 API internals.
 #[cfg(all(feature = "dx12", windows))]
-mod dx12;
-mod empty;
+pub mod dx12;
+/// A dummy API implementation.
+pub mod empty;
+/// GLES API internals.
 #[cfg(all(feature = "gles"))]
-mod gles;
+pub mod gles;
+/// Metal API internals.
 #[cfg(all(feature = "metal"))]
-mod metal;
+pub mod metal;
+/// Vulkan API internals.
 #[cfg(feature = "vulkan")]
-mod vulkan;
+pub mod vulkan;
 
 pub mod auxil;
 pub mod api {

wgpu/src/backend/direct.rs

@@ -128,7 +128,7 @@ impl Context {
         Ok((device, queue))
     }
 
-    #[cfg(any(not(target_arch = "wasm32"), feature = "emscripten"))]
+    #[cfg(any(not(target_arch = "wasm32"), feature = "emscripten", feature = "webgl"))]
     pub unsafe fn create_texture_from_hal<A: wgc::hub::HalApi>(
         &self,
         hal_texture: A::Texture,

wgpu/src/lib.rs

@@ -2118,7 +2118,7 @@ impl Device {
     /// - `hal_texture` must be created from this device internal handle
     /// - `hal_texture` must be created respecting `desc`
     /// - `hal_texture` must be initialized
-    #[cfg(any(not(target_arch = "wasm32"), feature = "emscripten"))]
+    #[cfg(any(not(target_arch = "wasm32"), feature = "emscripten", feature = "webgl"))]
     pub unsafe fn create_texture_from_hal<A: wgc::hub::HalApi>(
         &self,
         hal_texture: A::Texture,