The `surface` is used to create the `swap_chain`. Our `window` needs to implement [raw-window-handle](https://crates.io/crates/raw-window-handle)'s `HasRawWindowHandle` trait to access the native window implementation for `wgpu` to properly create the graphics backend. Fortunately, winit's `Window` fits the bill. We also need it to request our `adapter`.
The `features` field on `DeviceDescriptor`, allows us to specify what extra features we want. For this simple example, I've decided not to use any extra features.
The device you have limits the features you can use. If you want to use certain features you may need to limit what devices you support, or provide work arounds.
You can get a list of features supported by your device using `adapter.features()`, or `device.features()`.
The `limits` field describes the limit of certain types of resource we can create. We'll use the defaults for this tutorial, so we can support most devices. You can view a list of limits [here](https://docs.rs/wgpu/0.7.0/wgpu/struct.Limits.html).
Here we are defining and creating the `swap_chain`. The `usage` field describes how the `swap_chain`'s underlying textures will be used. `RENDER_ATTACHMENT` specifies that the textures will be used to write to the screen (we'll talk about more `TextureUsage`s later).
The `format` defines how the `swap_chain`s textures will be stored on the gpu. Different displays prefer different formats. We use `adapter.get_swap_chain_preferred_format()` to figure out the best format to use.
The `present_mode` uses the `wgpu::PresentMode` enum which determines how to sync the swap chain with the display. You can see all the options [in the docs](https://docs.rs/wgpu/0.7.0/wgpu/enum.PresentMode.html)
You can use libraries like [async_std](https://docs.rs/async_std) and [tokio](https://docs.rs/tokio) to make main async, so you can await futures. I've elected not to use these crates as this tutorial is not about writing an async application. We just need some way to interact with wgpu's async functions, and the [futures crate](https://docs.rs/futures) is enough for that.
If we want to support resizing in our application, we're going to need to recreate the `swap_chain` everytime the window's size changes. That's the reason we stored the physical `size` and the `sc_desc` used to create the swapchain. With all of these, the resize method is very simple.
`input()` returns a `bool` to indicate whether an event has been fully processed. If the method returns `true`, the main loop won't process the event any further.
We're just going to return false for now because we don't have any events we want to capture.
We need to do a little more work in the event loop. We want `State` to have priority over `main()`. Doing that (and previous changes) should have your loop looking like this.
Here's where the magic happens. First we need to get a frame to render to. This will include a `wgpu::Texture` and `wgpu::TextureView` that will hold the actual image we're drawing to (we'll cover this more when we talk about textures).
We also need to create a `CommandEncoder` to create the actual commands to send to the gpu. Most modern graphics frameworks expect commands to be stored in a command buffer before being sent to the gpu. The `encoder` builds a command buffer that we can then send to the gpu.
```rust
let mut encoder = self.device.create_command_encoder(&wgpu::CommandEncoderDescriptor {
Now we can actually get to clearing the screen (long time coming). We need to use the `encoder` to create a `RenderPass`. The `RenderPass` has all the methods to do the actual drawing. The code for creating a `RenderPass` is a bit nested, so I'll copy it all here, and talk about the pieces.
```rust
{
let _render_pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
First things first, let's talk about the `{}`. `encoder.begin_render_pass(...)` borrows `encoder` mutably (aka `&mut self`). We can't call `encoder.finish()` until we release that mutable borrow. The `{}` around `encoder.begin_render_pass(...)` tells rust to drop any variables within them when the code leaves that scope thus releasing the mutable borrow on `encoder` and allowing us to `finish()` it. If you don't like the `{}`, you can also use `drop(render_pass)` to achieve the same effect.
We can get the same results by removing the `{}`, and the `let _render_pass =` line, but we need access to the `_render_pass` in the next tutorial, so we'll leave it as is.
The last lines of the code tell `wgpu` to finish the command buffer, and to submit it to the gpu's render queue.
We need to update the event loop again to call this method. We'll also call update before it too.
A `RenderPassDescriptor` only has three fields: `label`, `color_attachments` and `depth_stencil_attachment`. The `color_attachements` describe where we are going to draw our color to. We'll use `depth_stencil_attachment` later, but we'll set it to `None` for now.
The `RenderPassColorAttachment` has the `view` field which informs `wgpu` what texture to save the colors to. In this case we specify `frame.view` that we created using `swap_chain.get_current_frame()`. This means that any colors we draw to this attachment will get drawn to the screen.
The `resolve_target` is the texture that will receive the resolved output. This will be the same as `attachment` unless multisampling is enabled. We don't need to specify this, so we leave it as `None`.
The `ops` field takes a `wpgu::Operations` object. This tells wgpu what to do with the colors on the screen (specified by `frame.view`). The `load` field tells wgpu how to handle colors stored from the previous frame. Currently we are clearing the screen with a bluish color.
It's not uncommon to not clear the screen if the screen is going to be completely covered up with objects. If your scene doesn't cover the entire screen however you can end up with something like this.
Modify the `input()` method to capture mouse events, and update the clear color using that. *Hint: you'll probably need to use `WindowEvent::CursorMoved`*.
