//! The adapter, the surface configuration and the target the GPU rigs share,
//! so no two of them can probe for a device or make a target in different
//! ways.

use wgpu::*;

/// An adapter on whatever this machine has, or `None` where there is none.
///
/// Probed rather than assumed: there may be no Vulkan adapter, and GL is what
/// is left when there is not.
///
/// The instance is leaked deliberately. A Vulkan loader may unload the driver
/// when the last one drops, which can fault as a thread that used it exits --
/// and every test runs on a spawned thread.
pub fn adapter() -> Option<Adapter> {
    let all = Instance::new(InstanceDescriptor::new_without_display_handle());
    let instance = match pollster::block_on(all.request_adapter(&RequestAdapterOptions::default()))
    {
        Ok(_) => all,
        Err(_) => Instance::new(InstanceDescriptor {
            backends: Backends::GL,
            ..InstanceDescriptor::new_without_display_handle()
        }),
    };
    let instance: &'static Instance = Box::leak(Box::new(instance));
    pollster::block_on(instance.request_adapter(&RequestAdapterOptions::default())).ok()
}

pub fn config(format: TextureFormat, size: u32) -> SurfaceConfiguration {
    SurfaceConfiguration {
        usage: TextureUsages::RENDER_ATTACHMENT,
        format,
        color_space: SurfaceColorSpace::Auto,
        width: size,
        height: size,
        present_mode: PresentMode::Fifo,
        desired_maximum_frame_latency: 2,
        alpha_mode: CompositeAlphaMode::Auto,
        view_formats: vec![],
    }
}

/// A square colour target to draw a pass into. `copy` adds the usage a rig
/// that reads the pixels back needs; one that only times the pass does not.
// This module is compiled into each rig target separately, so a helper the
// ones that make no target of their own do not call is dead code there.
#[allow(dead_code)]
pub fn target(device: &Device, format: TextureFormat, size: u32, copy: bool) -> Texture {
    device.create_texture(&TextureDescriptor {
        label: Some("gpu rig target"),
        size: Extent3d {
            width: size,
            height: size,
            depth_or_array_layers: 1,
        },
        mip_level_count: 1,
        sample_count: 1,
        dimension: TextureDimension::D2,
        format,
        usage: match copy {
            true => TextureUsages::RENDER_ATTACHMENT | TextureUsages::COPY_SRC,
            false => TextureUsages::RENDER_ATTACHMENT,
        },
        view_formats: &[],
    })
}