vkAcquireNextImageKHR的pImageIndex什么时候返回？

Question

我正在学习 Vulkan 的tutorial。我的理解是 vkAcquireNextImageKHR 在它完成之前返回，这就是为什么我们需要在 vkQueueSubmit 等待它完成，但如果是这样的话，如果 vkAcquireNextImageKHR 没有，我们怎么知道我们传递给 recordCommandBuffer 的 imageIndex 指向下一张图像执行完了吗？

void drawFrame() {
        vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
        vkResetFences(device, 1, &inFlightFences[currentFrame]);

        uint32_t imageIndex;
        vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);

        vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
        recordCommandBuffer(commandBuffers[currentFrame], imageIndex);

        VkSubmitInfo submitInfo{};
        submitInfo.sType = VK_STRUCTURE_TYPE_SUBMIT_INFO;

        VkSemaphore waitSemaphores[] = {imageAvailableSemaphores[currentFrame]};
        VkPipelineStageFlags waitStages[] = {VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT};
        submitInfo.waitSemaphoreCount = 1;
        submitInfo.pWaitSemaphores = waitSemaphores;
        submitInfo.pWaitDstStageMask = waitStages;

        submitInfo.commandBufferCount = 1;
        submitInfo.pCommandBuffers = &commandBuffers[currentFrame];

        VkSemaphore signalSemaphores[] = {renderFinishedSemaphores[currentFrame]};
        submitInfo.signalSemaphoreCount = 1;
        submitInfo.pSignalSemaphores = signalSemaphores;

        if (vkQueueSubmit(graphicsQueue, 1, &submitInfo, inFlightFences[currentFrame]) != VK_SUCCESS) {
            throw std::runtime_error("failed to submit draw command buffer!");
        }

        VkPresentInfoKHR presentInfo{};
        presentInfo.sType = VK_STRUCTURE_TYPE_PRESENT_INFO_KHR;

        presentInfo.waitSemaphoreCount = 1;
        presentInfo.pWaitSemaphores = signalSemaphores;

        VkSwapchainKHR swapChains[] = {swapChain};
        presentInfo.swapchainCount = 1;
        presentInfo.pSwapchains = swapChains;

        presentInfo.pImageIndices = &imageIndex;

        vkQueuePresentKHR(presentQueue, &presentInfo);

        currentFrame = (currentFrame + 1) % MAX_FRAMES_IN_FLIGHT;
    }

Answer 1

说

vkAcquireNextImageKHR

执行交换链图像获取操作会更正确。此操作使图像可用于您的应用程序以进行渲染。而函数返回时可能还没有完成的就是这个操作。

弄清楚要获取哪个图像与实际执行获取操作不是一回事。如果函数成功返回，那么它给你的索引就是将要获取的图像的索引。