[译]Vulkan教程(16)图形管道基础之总结
Conclusion 总结
We can now combine all of the structures and objects from the previous chapters to create the graphics pipeline! Here's the types of objects we have now, as a quick recap:
- Shader stages: the shader modules that define the functionality of the programmable stages of the graphics pipeline
- Fixed-function state: all of the structures that define the fixed-function stages of the pipeline, like input assembly, rasterizer, viewport and color blending
- Pipeline layout: the uniform and push values referenced by the shader that can be updated at draw time
- Render pass: the attachments referenced by the pipeline stages and their usage
我们现在可以将之前章节的所有结构体和对象组合起来to创建图形管道了！下面是我们有的对象的类型，快速回顾一下：
- Shader阶段：shader模块that定义可编程阶段的功能of图形管道。
- 固定功能状态：所有的结构体that定义固定功能阶段of管道，例如输入组装、光栅化、视口和颜色混合。
- 管道布局：uniform和push值that被shader引用that可以在绘制时更新。
- Render pass：附件that被管道阶段引用和附件的用法。
All of these combined fully define the functionality of the graphics pipeline, so we can now begin filling in the VkGraphicsPipelineCreateInfo structure at the end of the createGraphicsPipeline function. But before the calls to vkDestroyShaderModule because these are still to be used during the creation.
所有这些组合起来定义了图形管道的功能，所以我们可以开始填入VkGraphicsPipelineCreateInfo 结构体at createGraphicsPipeline 函数结尾。但是要在调用vkDestroyShaderModule 之前，因为这些在创建过程中还是在被用到。
VkGraphicsPipelineCreateInfo pipelineInfo = {}; pipelineInfo.sType = VK_STRUCTURE_TYPE_GRAPHICS_PIPELINE_CREATE_INFO; pipelineInfo.stageCount = 2; pipelineInfo.pStages = shaderStages;
We start by referencing the array of VkPipelineShaderStageCreateInfo structs.
开始时，我们引用VkPipelineShaderStageCreateInfo 结构体的数组。
pipelineInfo.pVertexInputState = &vertexInputInfo; pipelineInfo.pInputAssemblyState = &inputAssembly; pipelineInfo.pViewportState = &viewportState; pipelineInfo.pRasterizationState = &rasterizer; pipelineInfo.pMultisampleState = &multisampling; pipelineInfo.pDepthStencilState = nullptr; // Optional pipelineInfo.pColorBlendState = &colorBlending; pipelineInfo.pDynamicState = nullptr; // Optional
Then we reference all of the structures describing the fixed-function stage.
然后我们引用描述固定功能阶段的所有结构体。
pipelineInfo.layout = pipelineLayout;
After that comes the pipeline layout, which is a Vulkan handle rather than a struct pointer.
然后是管道布局，which是一个Vulkan句柄，而不是结构体指针。
pipelineInfo.renderPass = renderPass; pipelineInfo.subpass = 0;
And finally we have the reference to the render pass and the index of the sub pass where this graphics pipeline will be used. It is also possible to use other render passes with this pipeline instead of this specific instance, but they have to be compatible with renderPass. The requirements for compatibility are described here, but we won't be using that feature in this tutorial.
最后，我们引用render pass和subpass的索引where图形管道会用到。有可能这个管道还使用另一个render pass，而不是这个，但它们必须与renderPass兼容。对于兼容要求在here，但本教程中我们不会用到这个特性。
pipelineInfo.basePipelineHandle = VK_NULL_HANDLE; // Optional pipelineInfo.basePipelineIndex = -1; // Optional
There are actually two more parameters: basePipelineHandle and basePipelineIndex. Vulkan allows you to create a new graphics pipeline by deriving from an existing pipeline. The idea of pipeline derivatives is that it is less expensive to set up pipelines when they have much functionality in common with an existing pipeline and switching between pipelines from the same parent can also be done quicker. You can either specify the handle of an existing pipeline with basePipelineHandle or reference another pipeline that is about to be created by index with basePipelineIndex. Right now there is only a single pipeline, so we'll simply specify a null handle and an invalid index. These values are only used if the VK_PIPELINE_CREATE_DERIVATIVE_BIT flag is also specified in the flags field of VkGraphicsPipelineCreateInfo.
其实还有2个参数：basePipelineHandle 和basePipelineIndex。Vulkan允许你创建新图形管道by继承一个已有的管道。这个管道继承的思想是，它比较省资源when它们很多功能相同with一个现有的管道，and在同一父管道下的管道之间切换也会更快。你可以要么用basePipelineHandle 指定一个现有管道的句柄，要么引用另一个管道that即将被创建by basePipelineIndex索引。现在只有一个管道，所以我们简单地指定一个null句柄和一个无效的索引即可。这些值只会在VK_PIPELINE_CREATE_DERIVATIVE_BIT 标志也在VkGraphicsPipelineCreateInfo的flags 字段指定时用到。
Now prepare for the final step by creating a class member to hold the VkPipeline object:
现在准备好最后的步骤by创建一个类成员to记录VkPipeline 对象。
VkPipeline graphicsPipeline;
And finally create the graphics pipeline:
最后创建图形管道：
if (vkCreateGraphicsPipelines(device, VK_NULL_HANDLE, 1, &pipelineInfo, nullptr, &graphicsPipeline) != VK_SUCCESS) { throw std::runtime_error("failed to create graphics pipeline!"); }
The vkCreateGraphicsPipelines function actually has more parameters than the usual object creation functions in Vulkan. It is designed to take multiple VkGraphicsPipelineCreateInfo objects and create multiple VkPipelineobjects in a single call.
vkCreateGraphicsPipelines 函数实际上有更多的参数that通常的对象创建函数in Vulkan。它被设计to接收多个VkGraphicsPipelineCreateInfo 对象and创建多个VkPipelineobjects对象in一个调用。
The second parameter, for which we've passed the VK_NULL_HANDLE argument, references an optional VkPipelineCache object. A pipeline cache can be used to store and reuse data relevant to pipeline creation across multiple calls to vkCreateGraphicsPipelines and even across program executions if the cache is stored to a file. This makes it possible to significantly speed up pipeline creation at a later time. We'll get into this in the pipeline cache chapter.
第二个参数，我们传入了VK_NULL_HANDLE ，其引用一个可选的VkPipelineCache 对象。一个管道缓存可以被用于保存和复用数据that与管道创建相关-在多次调用vkCreateGraphicsPipelines 中，甚至在多次程序执行中if缓存被保存到了文件中。这样就又可能to显著地加速管道创建at以后。我们将在后续章节详谈管道缓存。
The graphics pipeline is required for all common drawing operations, so it should also only be destroyed at the end of the program:
图形管道是必要的for所有常用绘制操作，所以它只应该在程序结尾时被销毁：
void cleanup() { vkDestroyPipeline(device, graphicsPipeline, nullptr); vkDestroyPipelineLayout(device, pipelineLayout, nullptr); ... }
Now run your program to confirm that all this hard work has resulted in a successful pipeline creation! We are already getting quite close to seeing something pop up on the screen. In the next couple of chapters we'll set up the actual framebuffers from the swap chain images and prepare the drawing commands.
现在运行你的程序to确认that所有这些艰苦努力成功地创建了管道对象！我们已经很接近to看到屏幕上显示点东西了。接下来的几章我们将设置帧缓存from交换链image，并准备绘制命令。
C++ code / Vertex shader / Fragment shader
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