Jérôme Bousquié
73 lines
3.0 KiB
Markdown
73 lines
3.0 KiB
Markdown
# DRAFT — Frame Loop
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## The "Frame Loop" (preparing the draw)
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To display something, you must follow an immutable cycle called the **Frame Lifetime**. In your Renderer (or a dedicated method of Context), you will need to:
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1. **Acquire a surface texture** — ask the surface for the Back Buffer texture (where you'll draw).
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2. **Create a texture view** — WGPU doesn't draw directly on the texture, but on a "view" into that texture.
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3. **Create a command encoder** — this is the notebook where you write your orders ("clear screen", "draw triangle", "finalize").
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4. **Submit commands** — send this notebook to the GPU via the Queue.
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### Why this is the logical next step
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Because without this, your `configure` call does nothing. You've reserved space on the GPU; now you need to learn how to "grasp" it to work on it.
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Here is the skeleton of this cycle that you should implement:
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```rust
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// In your Renderer (or Context)
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pub fn render(&self) -> Result<(), WsgError> {
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// 1. Acquire the texture to draw on
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let frame = self.surface.get_current_texture()
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.map_err(|_| WsgError::SurfaceIncompatible)?;
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// 2. Create the view (the "channel" to the texture)
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let view = frame.texture.create_view(&wgpu::TextureViewDescriptor::default());
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// 3. Create the command encoder
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let mut encoder = self.device.create_command_encoder(&wgpu::CommandEncoderDescriptor {
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label: Some("Render Encoder"),
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});
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// --- This is where we'll draw later ---
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{
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let _render_pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
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label: Some("Render Pass"),
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color_attachments: &[Some(wgpu::RenderPassColorAttachment {
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view: &view,
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resolve_target: None,
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ops: wgpu::Operations {
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load: wgpu::LoadOp::Clear(wgpu::Color::BLUE), // Blue background for testing
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store: wgpu::StoreOp::Store,
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},
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})],
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depth_stencil_attachment: None,
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timestamp_writes: None,
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occlusion_query_set: None,
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});
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}
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// 4. Submit and present
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self.queue.submit(std::iter::once(encoder.finish()));
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frame.present();
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Ok(())
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}
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```
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### Why this separation is vital
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You'll notice that the `{ let _render_pass ... }` block is delimited by braces. This is very important in Rust: `render_pass` must be dropped before calling `encoder.finish()`. If you forget this, your program will crash because you'd be submitting orders while the "notebook" is still being written.
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## Persistent vs. Per-Frame Resources
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| Element | Lifetime | Why? |
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|---------|----------|------|
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| `SurfaceConfiguration` | Persistent | Only changes on resize |
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| `RenderPipeline` | Persistent | Very expensive to create (shader compilation) |
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| Buffers (Vertex/Index) | Persistent | Geometry data doesn't change every frame |
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| `CommandEncoder` | Frame | Temporary "notebook" for frame commands |
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| `TextureView` | Frame | View into the active Swapchain texture |
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