hal/gles: support externally initialized contexts

wgpu-hal/Cargo.toml

@@ -19,6 +19,13 @@ gles = ["naga/glsl-out", "glow", "egl", "libloading"]
 dx12 = ["naga/hlsl-out", "native", "bit-set", "range-alloc", "winapi/d3d12", "winapi/d3d12shader", "winapi/d3d12sdklayers", "winapi/dxgi1_6"]
 renderdoc = ["libloading", "renderdoc-sys"]
 
+[[example]]
+name = "halmark"
+
+[[example]]
+name = "raw-gles"
+required-features = ["gles"]
+
 [dependencies]
 bitflags = "1.0"
 parking_lot = "0.11"
@@ -86,4 +93,5 @@ features = ["wgsl-in"]
 
 [dev-dependencies]
 env_logger = "0.8"
-winit = "0.26"
+winit = "0.26" # for "halmark" example
+glutin = "0.28" # for "gles" example

wgpu-hal/examples/halmark/main.rs

@@ -1,3 +1,5 @@
+//! This example shows basic usage of wgpu-hal by rendering
+//! a ton of moving sprites, each with a separate texture and draw call.
 extern crate wgpu_hal as hal;
 
 use hal::{

wgpu-hal/examples/raw-gles.rs

@@ -0,0 +1,118 @@
+//! This example shows interop with raw GLES contexts -
+//! the ability to hook up wgpu-hal to an existing context and draw into it.
+
+extern crate wgpu_hal as hal;
+use hal::{Adapter as _, CommandEncoder as _, Device as _, Queue as _};
+
+fn main() {
+    env_logger::init();
+    println!("Initializing external GL context");
+
+    let event_loop = glutin::event_loop::EventLoop::new();
+    let window_builder = glutin::window::WindowBuilder::new();
+    let gl_context = unsafe {
+        glutin::ContextBuilder::new()
+            .with_gl(glutin::GlRequest::Specific(glutin::Api::OpenGlEs, (3, 0)))
+            .build_windowed(window_builder, &event_loop)
+            .unwrap()
+            .make_current()
+            .unwrap()
+    };
+    let inner_size = gl_context.window().inner_size();
+
+    println!("Hooking up to wgpu-hal");
+    let exposed = unsafe {
+        <hal::api::Gles as hal::Api>::Adapter::new_external(|name| {
+            gl_context.get_proc_address(name)
+        })
+    }
+    .expect("GL adapter can't be initialized");
+    let mut od = unsafe {
+        exposed
+            .adapter
+            .open(wgt::Features::empty(), &wgt::Limits::downlevel_defaults())
+    }
+    .unwrap();
+
+    let format = wgt::TextureFormat::Rgba8UnormSrgb;
+    let texture = <hal::api::Gles as hal::Api>::Texture::default_framebuffer(format);
+    let view = unsafe {
+        od.device
+            .create_texture_view(
+                &texture,
+                &hal::TextureViewDescriptor {
+                    label: None,
+                    format,
+                    dimension: wgt::TextureViewDimension::D2,
+                    usage: hal::TextureUses::COLOR_TARGET,
+                    range: wgt::ImageSubresourceRange::default(),
+                },
+            )
+            .unwrap()
+    };
+
+    println!("Filling the screen");
+    let mut encoder = unsafe {
+        od.device
+            .create_command_encoder(&hal::CommandEncoderDescriptor {
+                label: None,
+                queue: &od.queue,
+            })
+            .unwrap()
+    };
+    let rp_desc = hal::RenderPassDescriptor {
+        label: None,
+        extent: wgt::Extent3d {
+            width: inner_size.width,
+            height: inner_size.height,
+            depth_or_array_layers: 1,
+        },
+        sample_count: 1,
+        color_attachments: &[hal::ColorAttachment {
+            target: hal::Attachment {
+                view: &view,
+                usage: hal::TextureUses::COLOR_TARGET,
+            },
+            resolve_target: None,
+            ops: hal::AttachmentOps::STORE,
+            clear_value: wgt::Color::BLUE,
+        }],
+        depth_stencil_attachment: None,
+        multiview: None,
+    };
+    unsafe {
+        encoder.begin_encoding(None).unwrap();
+        encoder.begin_render_pass(&rp_desc);
+        encoder.end_render_pass();
+        let cmd_buf = encoder.end_encoding().unwrap();
+        od.queue.submit(&[&cmd_buf], None).unwrap();
+    }
+
+    println!("Showing the window");
+    gl_context.swap_buffers().unwrap();
+
+    event_loop.run(move |event, _, control_flow| {
+        use glutin::{
+            event::{Event, KeyboardInput, VirtualKeyCode, WindowEvent},
+            event_loop::ControlFlow,
+        };
+        *control_flow = ControlFlow::Wait;
+
+        match event {
+            Event::LoopDestroyed => return,
+            Event::WindowEvent { event, .. } => match event {
+                WindowEvent::CloseRequested
+                | WindowEvent::KeyboardInput {
+                    input:
+                        KeyboardInput {
+                            virtual_keycode: Some(VirtualKeyCode::Escape),
+                            ..
+                        },
+                    ..
+                } => *control_flow = ControlFlow::Exit,
+                _ => (),
+            },
+            _ => (),
+        }
+    });
+}