Fabrice R
Fabrice R

Reputation: 11

In my Vulkan program, how to implement synchronisation to avoid displaying image in wrong order?

I'm writing a Vulkan program. I have a problem with image being sometimes displayed in wrong order. Here is the part I suppose where things to go wrong. For information, I have 2 frames in flight (MAX_FRAMES_IN_FLIGHT), and 3 images (swapChainSupport.capabilities.minImageCount + 1). The two function below are called in my main loop:

// main loop content (simplified)
vcSwapChain->acquireNextImage(&currentImageIndex);
//... Do render stuff, set command buffer
vcSwapChain->submitCommandBuffers(&commandBuffer, &currentImageIndex);
VkResult FwSwapChain::acquireNextImage(uint32_t* imageIndex) {
    vkWaitForFences(device.getDevice(), 2, frameInFlightFences.data(), VK_TRUE, UINT64_MAX);

    VkResult result = vkAcquireNextImageKHR(device.getDevice(), vkSwapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, imageIndex);

    return result;
}
VkResult FwSwapChain::submitCommandBuffers(const VkCommandBuffer* buffers, uint32_t* 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 = buffers;

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

    vkResetFences(device.getDevice(), 1, &frameInFlightFences[currentFrame]);
    if (vkQueueSubmit(device.getGraphicsQueue(), 1, &submitInfo, frameInFlightFences[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[] = { vkSwapChain };
    presentInfo.swapchainCount = 1;
    presentInfo.pSwapchains = swapChains;

    presentInfo.pImageIndices = imageIndex;

    auto result = vkQueuePresentKHR(device.getPresentQueue(), &presentInfo);

    currentFrame = (currentFrame + 1) % MAX_FRAMES_IN_FLIGHT;

    return result;
}

If i set MAX_FRAMES_IN_FLIGHT to 1, then I haven't the problem.

Upvotes: 1

Views: 26

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