Question

因此，我有一个渲染通道，其中有一个子通道，可直接绘制到帧缓冲区。该规范不会强迫我使用依赖项-如果我忽略它们，实现会隐式插入它们（尽管我不明白为什么它在第一个子通道中使用srcStageMask = VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT-这个阶段意味着最开始，即等什么）。

但是与Vulkan一样，更好-明确一点。这就是混乱-多个来源使用不同的子通行证。

SDK的多维数据集示例根本不使用它们。

Vulkan教程仅使用一个：

dependency.srcSubpass = VK_SUBPASS_EXTERNAL;
dependency.dstSubpass = 0;
dependency.srcStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
dependency.srcAccessMask = 0;
dependency.dstStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
dependency.dstAccessMask = VK_ACCESS_COLOR_ATTACHMENT_READ_BIT | VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;

为什么srcAccessMask在这里为零？

没有秘密的API使用两个：

dependency.srcSubpass = VK_SUBPASS_EXTERNAL;
dependency.dstSubpass = 0;
dependency.srcStageMask = VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT;
dependency.srcAccessMask = VK_ACCESS_MEMORY_READ_BIT;
dependency.dstStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
dependency.dstAccessMask = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;

和

dependency.srcSubpass = 0;
dependency.dstSubpass = VK_SUBPASS_EXTERNAL;
dependency.srcStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
dependency.srcAccessMask = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;
dependency.dstStageMask = VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT;
dependency.dstAccessMask = VK_ACCESS_MEMORY_READ_BIT;

不清楚srcStageMask为何第一个子阶段中的VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT-不是这个阶段应该用于执行依赖，但是在这里我们需要内存依赖吗？关于为什么dstStageMask的相同问题 VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT在第二个子通道中？

Khronos同步示例使用以下示例：

dependency.srcSubpass = VK_SUBPASS_EXTERNAL;
dependency.dstSubpass = 0;
dependency.srcStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
dependency.srcAccessMask = 0;
dependency.dstStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
dependency.dstAccessMask = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;

为什么srcAccessMask为0？

这是我对两个依赖项的尝试：

    dependency.srcSubpass = VK_SUBPASS_EXTERNAL;
    dependency.dstSubpass = 0;
    dependency.srcStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT; // need to wait until
presentation is finished reading the image
    dependency.srcAccessMask = VK_ACCESS_COLOR_ATTACHMENT_READ_BIT;
    dependency.dstStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT; // we are writing to
the image in this stage
    dependency.dstAccessMask = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;

and

    dependency.srcSubpass = 0;
    dependency.dstSubpass = VK_SUBPASS_EXTERNAL;
    dependency.srcStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT; // we are writing to
the image in this stage
    dependency.srcAccessMask = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;
    dependency.dstStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT; // presentation reads
image in this stage (is it?)
    dependency.dstAccessMask = VK_ACCESS_COLOR_ATTACHMENT_READ_BIT;

所有这些都很令人困惑。如您所见，多个主管资源的看法不同。使用哪一个？如何理解这些依赖性？

Answer 1

哦，亲爱的，这是一个大多数人不太了解的话题。假定并传播了许多错误信息。规范示例的正确位置是wikipage in the github repo。

有关交换链图像获取/呈现的相关部分可以在here中找到。

这是一个旧示例，之前没有正确确定许多同步细节。
这样做的目的是使信号量同步，以等待vkAcquireNextImage结果与渲染一起使用。这是写后读取的危险，并且信号量将包括内存可见性同步。因此srcAccessMask是不必要的。
同样，障碍是指与信号量同步。将命令缓冲区提交到队列时，您可以设置哪些阶段等待哪些信号量。在这种情况下，他们使用管道级的底部而不是VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT
答案与2相同，唯一的不同是与dstAccessMask

我上面链接的Wiki页面使用以下内容：

/* Only need a dependency coming in to ensure that the first
   layout transition happens at the right time.
   Second external dependency is implied by having a different
   finalLayout and subpass layout. */
VkSubpassDependency dependency = {
    .srcSubpass = VK_SUBPASS_EXTERNAL,
    .dstSubpass = 0,
    // .srcStageMask needs to be a part of pWaitDstStageMask in the WSI semaphore.
    .srcStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT,
    .dstStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT,
    .srcAccessMask = 0,
    .dstAccessMask = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT,
    .dependencyFlags = 0};

/* Normally, we would need an external dependency at the end as well since we are changing layout in finalLayout,
   but since we are signalling a semaphore, we can rely on Vulkan's default behavior,
   which injects an external dependency here with
   dstStageMask = VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT,
   dstAccessMask = 0. */

您混合了第二个障碍的子通过索引。尽管如评论中所述，渲染通道的末尾已经存在一个隐式障碍，该障碍又与您用来与当前同步的信号量或栅栏同步。因此，不需要显式依赖。

单个子通道的子通道依赖关系。如何？

1 个答案: