Crafter.Graphics/tests/SwapchainTransferDst/main.cpp

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

// The swapchain images are created with TRANSFER_DST where the surface
// allows it, so a pass can blit or clear into them: the swapchain used to be
// STORAGE | TRANSFER_SRC only, which left a compute shader as the only way to
// put an offscreen image on screen. This checks the usage the Window records,
// then clears the swapchain image from a pass, reads the frame back and
// checks the colour.
//
// Needs a live Wayland compositor and a Vulkan device. The validation check
// only means something with CRAFTER_GRAPHICS_VALIDATION set.

#include <cstdlib>
#include "vulkan/vulkan.h"

// PNG decode for the read-back frame. The library only compiles the writer
// (Window::CaptureNextFrame); STB_IMAGE_STATIC keeps the reader private to this file.
#define STB_IMAGE_IMPLEMENTATION
#define STB_IMAGE_STATIC
#define STBI_ONLY_PNG
#include "../../lib/stb_image.h"

import Crafter.Graphics;
import std;
using namespace Crafter;
namespace fs = std::filesystem;

namespace {

int failures = 0;

void Check(bool ok, std::string_view what) {
    std::println("{}  {}", ok ? "PASS" : "FAIL", what);
    if (!ok) ++failures;
}

// Clears the frame's swapchain image with vkCmdClearColorImage, a transfer
// write.
struct ClearPass : RenderPass {
    VkClearColorValue colour = {{0.2f, 0.4f, 0.8f, 1.0f}};

    void Record(VkCommandBuffer cmd, std::uint32_t, Window& window) override {
        const VkImageSubresourceRange range = {VK_IMAGE_ASPECT_COLOR_BIT, 0, 1, 0, 1};
        vkCmdClearColorImage(cmd, window.images[window.currentBuffer], VK_IMAGE_LAYOUT_GENERAL, &colour, 1, &range);
    }

    VkPipelineStageFlags SwapchainStage() const override {
        return VK_PIPELINE_STAGE_TRANSFER_BIT;
    }
};

} // namespace

int main() {
    Device::Initialize();
    Device::validationErrorCount = 0;

    Window window(320, 240, "SwapchainTransferDst test");
    VkSurfaceCapabilitiesKHR caps;
    Device::CheckVkResult(vkGetPhysicalDeviceSurfaceCapabilitiesKHR(Device::physDevice, window.vulkanSurface, &caps));
    const bool surfaceAllows = (caps.supportedUsageFlags & VK_IMAGE_USAGE_TRANSFER_DST_BIT) != 0;

    Check((window.swapchainUsage & (VK_IMAGE_USAGE_STORAGE_BIT | VK_IMAGE_USAGE_TRANSFER_SRC_BIT))
              == (VK_IMAGE_USAGE_STORAGE_BIT | VK_IMAGE_USAGE_TRANSFER_SRC_BIT),
          "the swapchain keeps STORAGE and TRANSFER_SRC");
    Check(((window.swapchainUsage & VK_IMAGE_USAGE_TRANSFER_DST_BIT) != 0) == surfaceAllows,
          std::format("TRANSFER_DST is used exactly when the surface allows it ({})", surfaceAllows ? "it does" : "it doesn't"));
    if (!surfaceAllows) {
        std::println("SKIP  the clear-and-read-back check (this surface has no TRANSFER_DST)");
        return failures == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
    }

    window.StartInit();
    window.FinishInit();
    ClearPass clear;
    window.passes.push_back(&clear);
    for (int i = 0; i < Window::numFrames * 2; ++i) window.Render();
    Device::CheckVkResult(vkQueueWaitIdle(Device::queue));

    const fs::path out = fs::temp_directory_path() / "crafter-swapchain-transfer-dst.png";
    std::error_code ec;
    fs::remove(out, ec);
    window.CaptureNextFrame(out);
    window.Render();
    if (std::getenv("CRAFTER_GRAPHICS_VALIDATION") != nullptr) {
        Check(Device::validationErrorCount == 0,
              std::format("no Vulkan validation errors while clearing and capturing ({} seen)", Device::validationErrorCount));
    }
    int width = 0, height = 0, channels = 0;
    stbi_uc* pixels = stbi_load(out.string().c_str(), &width, &height, &channels, STBI_rgb_alpha);
    Check(pixels != nullptr, "the frame was read back");
    if (pixels != nullptr) {
        const stbi_uc* p = pixels + (static_cast<std::size_t>(height / 2) * width + width / 2) * 4;
        // 0.2, 0.4, 0.8 in a UNORM image.
        const bool cleared = std::abs(p[0] - 51) <= 2 && std::abs(p[1] - 102) <= 2 && std::abs(p[2] - 204) <= 2;
        Check(cleared, std::format("the cleared colour reached the frame (got {}, {}, {})", p[0], p[1], p[2]));
        stbi_image_free(pixels);
    }

    Device::CheckVkResult(vkQueueWaitIdle(Device::queue));
    std::println("{}", failures == 0 ? "all checks passed" : "check(s) failed");
    return failures == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
}