wsg/docs/DRAFT.md

DRAFT — Frame Loop

The "Frame Loop" (preparing the draw)

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:

1. Acquire a surface texture — ask the surface for the Back Buffer texture (where you'll draw).
2. Create a texture view — WGPU doesn't draw directly on the texture, but on a "view" into that texture.
3. Create a command encoder — this is the notebook where you write your orders ("clear screen", "draw triangle", "finalize").
4. Submit commands — send this notebook to the GPU via the Queue.

Why this is the logical next step

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.

Here is the skeleton of this cycle that you should implement:

// In your Renderer (or Context)
pub fn render(&self) -> Result<(), WsgError> {
    // 1. Acquire the texture to draw on
    let frame = self.surface.get_current_texture()
        .map_err(|_| WsgError::SurfaceIncompatible)?;

    // 2. Create the view (the "channel" to the texture)
    let view = frame.texture.create_view(&wgpu::TextureViewDescriptor::default());

    // 3. Create the command encoder
    let mut encoder = self.device.create_command_encoder(&wgpu::CommandEncoderDescriptor {
        label: Some("Render Encoder"),
    });

    // --- This is where we'll draw later ---
    {
        let _render_pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
            label: Some("Render Pass"),
            color_attachments: &[Some(wgpu::RenderPassColorAttachment {
                view: &view,
                resolve_target: None,
                ops: wgpu::Operations {
                    load: wgpu::LoadOp::Clear(wgpu::Color::BLUE), // Blue background for testing
                    store: wgpu::StoreOp::Store,
                },
            })],
            depth_stencil_attachment: None,
            timestamp_writes: None,
            occlusion_query_set: None,
        });
    }

    // 4. Submit and present
    self.queue.submit(std::iter::once(encoder.finish()));
    frame.present();

    Ok(())
}

Why this separation is vital

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.

Persistent vs. Per-Frame Resources

Element	Lifetime	Why?
SurfaceConfiguration	Persistent	Only changes on resize
RenderPipeline	Persistent	Very expensive to create (shader compilation)
Buffers (Vertex/Index)	Persistent	Geometry data doesn't change every frame
CommandEncoder	Frame	Temporary "notebook" for frame commands
TextureView	Frame	View into the active Swapchain texture