Crafter.Graphics/tests/DeviceSelection/main.cpp

//SPDX-License-Identifier: LGPL-3.0-only
//SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®

// CRAFTER_GRAPHICS_DEVICE picks the GPU by its number among the distinct
// GPUs in the Vulkan loader's list. Without it the first discrete GPU is
// used, as before. A machine with two of the same GPU had no way to render on
// the second, which matters when the first is full: a job filling its memory
// leaves no room to even create a device there. A GPU listed twice, as a
// Flatpak with two driver manifests lists them, counts once. A value that
// isn't a number (a PCI address, say) is an error, as one out of range is: it
// used to pick the first GPU without a word.
//
// Needs at least two distinct GPUs; skips with fewer.

#include <cstdlib>
#include <sys/wait.h>
#include <unistd.h>
#include "vulkan/vulkan.h"

import Crafter.Graphics;
import std;
using namespace Crafter;

int main() {
    // In a child, before this process has a Vulkan instance.
    const pid_t child = fork();
    if (child == 0) {
        setenv("CRAFTER_GRAPHICS_DEVICE", "CA:00.0", 1);
        try {
            Device::Initialize();
        } catch (const std::runtime_error& error) {
            _exit(std::string_view(error.what()).find("CRAFTER_GRAPHICS_DEVICE") != std::string_view::npos ? 0 : 2);
        }
        _exit(1);
    }
    int status = 0;
    waitpid(child, &status, 0);
    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
        std::println("FAIL  CRAFTER_GRAPHICS_DEVICE=CA:00.0 is an error naming the variable (child exit {})", WIFEXITED(status) ? WEXITSTATUS(status) : -1);
        return EXIT_FAILURE;
    }
    std::println("PASS  CRAFTER_GRAPHICS_DEVICE=CA:00.0 is an error naming the variable");

    setenv("CRAFTER_GRAPHICS_DEVICE", "1", 1);
    Device::Initialize();

    std::uint32_t count = 0;
    vkEnumeratePhysicalDevices(Device::instance, &count, nullptr);
    std::vector<VkPhysicalDevice> devices(count);
    vkEnumeratePhysicalDevices(Device::instance, &count, devices.data());
    // The distinct GPUs, by device UUID, in the loader's order.
    std::vector<std::array<std::uint8_t, VK_UUID_SIZE>> distinct;
    auto uuidOf = [](VkPhysicalDevice device) {
        VkPhysicalDeviceIDProperties id { .sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_ID_PROPERTIES };
        VkPhysicalDeviceProperties2 properties { .sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_PROPERTIES_2, .pNext = &id };
        vkGetPhysicalDeviceProperties2(device, &properties);
        std::array<std::uint8_t, VK_UUID_SIZE> uuid;
        std::ranges::copy(id.deviceUUID, uuid.begin());
        return uuid;
    };
    for (VkPhysicalDevice device : devices) {
        if (std::ranges::find(distinct, uuidOf(device)) == distinct.end()) distinct.push_back(uuidOf(device));
    }
    if (distinct.size() < 2) {
        std::println("SKIP  one GPU; nothing to choose between");
        return 77;
    }

    const bool picked = uuidOf(Device::physDevice) == distinct[1];
    std::println("{}  CRAFTER_GRAPHICS_DEVICE=1 selects the second distinct GPU ({}, {} listed)",
                 picked ? "PASS" : "FAIL", Device::deviceProperties.deviceName, count);
    return picked ? EXIT_SUCCESS : EXIT_FAILURE;
}