ai-app/rigs/gpu-probe/src/main.rs

//! Ask a device whether it can give iris the GPU it asks for.
//!
//! Until 2026-09-04 iris's renderer bound every texture it had drawn as one
//! binding array and indexed it non-uniformly from the shader, which needed
//! descriptor indexing and a very large per-stage binding-array limit
//! (101,000 elements: 100,000 textures and 1,000 samplers,
//! `UiLimits::default`). That was ordinary on a desktop and, per
//! TEXTURES.md's "iris's binding array does not survive real Android
//! hardware", not available on a real share of Android GPUs -- and it failed
//! outright on this emulator's software Vulkan, which is what this rig
//! caught first. iris now asks for nothing beyond wgpu's own defaults (see
//! `iris/src/default/render.rs`): the glyph atlas is one `texture_2d_array`
//! and a standalone image is its own ordinary bind group, and neither needs
//! descriptor indexing. This rig still asks `request_device` for exactly
//! what iris asks for, so it keeps being the answer to "does iris's actual
//! device request succeed here" rather than a guess from reading the code.
//!
//! It runs as a plain executable with no window and no APK, because
//! `request_adapter` needs no surface -- so it can be pushed to a device with
//! `adb push` and run from `/data/local/tmp`, which is far cheaper than an
//! app. What it therefore cannot answer is anything about presenting to a
//! surface; that is the Android backend's own problem.

mod vk;

use wgpu::*;

/// What `iris/src/default/render.rs` asks `request_device` for, now that the
/// binding array is gone: nothing beyond wgpu's own default feature set.
fn iris_features() -> Features {
    Features::empty()
}

/// The one non-default limit iris asks for -- unrelated to the binding array,
/// kept for the big storage buffers behind rects/glyphs.
const IRIS_MAX_BUFFER_SIZE: u64 = 1 << 30;

/// Mirrors `iris_core::device_limits()` (`iris/core/src/render/mod.rs`) --
/// cannot call it directly, since this rig is deliberately its own crate,
/// not a workspace member (this file's own Cargo.toml comment). Keep the
/// two in sync by hand when one changes; this rig's whole purpose is "does
/// the device iris actually builds come back," so a stale copy here would
/// silently stop answering that question. Zeroed rather than left at
/// `Limits::default()`'s desktop-tier values because nothing in iris
/// creates a `ComputePipeline` or a `@compute` shader stage -- found by
/// grepping the whole `iris`/`iris-core` tree before this rig's comment was
/// written -- and the unconditional default request is what crashed
/// `request_device` on the Android emulator's software GL path
/// (`EMU_GPU=software`, `force-gles`: SwiftShader's GL reports itself as
/// OpenGL ES 3.0, which has no compute shaders at all, so the adapter's
/// real limit is 0). The same would happen on a real GLES-3.0-only Android
/// device.
fn iris_limits() -> Limits {
    Limits {
        max_buffer_size: IRIS_MAX_BUFFER_SIZE,
        max_compute_workgroup_storage_size: 0,
        max_compute_invocations_per_workgroup: 0,
        max_compute_workgroup_size_x: 0,
        max_compute_workgroup_size_y: 0,
        max_compute_workgroup_size_z: 0,
        max_compute_workgroups_per_dimension: 0,
        ..Default::default()
    }
}

fn main() {
    vk::report();

    let instance = Instance::new(&InstanceDescriptor {
        backends: Backends::from_env().unwrap_or(Backends::PRIMARY),
        ..Default::default()
    });

    let adapters = pollster::block_on(instance.enumerate_adapters(Backends::all()));
    println!("adapters: {}", adapters.len());
    for adapter in &adapters {
        let info = adapter.get_info();
        println!(
            "  {:?} {} ({:?})",
            info.backend, info.name, info.device_type
        );
    }

    let Some(adapter) = pollster::block_on(instance.request_adapter(&RequestAdapterOptions {
        power_preference: PowerPreference::default(),
        compatible_surface: None,
        force_fallback_adapter: false,
    }))
    .ok() else {
        println!("\nNO ADAPTER");
        std::process::exit(1);
    };

    let info = adapter.get_info();
    println!(
        "\nchosen: {:?} {} ({:?})",
        info.backend, info.name, info.device_type
    );
    println!("driver: {} {}", info.driver, info.driver_info);

    let have = adapter.features();
    println!("\nfeatures iris requires:");
    let mut missing = Features::empty();
    for f in iris_features().iter() {
        let ok = have.contains(f);
        println!(
            "  {:60} {}",
            format!("{f:?}"),
            if ok { "yes" } else { "NO" }
        );
        if !ok {
            missing |= f;
        }
    }

    let limits = adapter.limits();
    println!("\nlimits iris requires:");
    println!(
        "  {:52} want {:>7}  have {:>7}  {}",
        "max_buffer_size",
        IRIS_MAX_BUFFER_SIZE,
        limits.max_buffer_size,
        if limits.max_buffer_size >= IRIS_MAX_BUFFER_SIZE {
            "ok"
        } else {
            "TOO SMALL"
        }
    );

    // The question that actually matters: does the device iris builds come
    // back, or does wgpu refuse it? With no features and no binding-array
    // limits requested, this is expected to succeed everywhere -- this rig
    // is what turned that from an assumption into a measurement, first on
    // this emulator's software Vulkan.
    let wanted = iris_limits();
    match pollster::block_on(adapter.request_device(&DeviceDescriptor {
        required_features: iris_features(),
        required_limits: wanted,
        ..Default::default()
    })) {
        Ok(_) => println!("\nIRIS DEVICE: ok"),
        Err(e) => println!("\nIRIS DEVICE: FAILED -- {e}"),
    }

    if !missing.is_empty() {
        println!("\nmissing features: {missing:?}");
    }
}