Module vulkano::pipeline

Describes a graphical or compute operation.

In Vulkan, before you can add a draw or a compute command to a command buffer you have to create a pipeline object that describes this command.

When you create a pipeline object, the implementation will usually generate some GPU machine code that will execute the operation (similar to a compiler that generates an executable for the CPU). Consequently it is a CPU-intensive operation that should be performed at initialization or during a loading screen.

There are two kinds of pipelines:

• ComputePipelines, for compute operations (general-purpose operations that read/write data in buffers or raw pixels in images).
• GraphicsPipelines, for graphical operations (operations that take vertices as input and write pixels to a framebuffer).

Creating a compute pipeline.

In order to create a compute pipeline, you first need a shader entry point.

TODO: write the rest For now vulkano has no "clean" way to create shaders ; everything's a bit hacky

Creating a graphics pipeline

A graphics operation takes vertices or vertices and indices as input, and writes pixels to a framebuffer. It consists of multiple steps:

• A shader named the vertex shader is run once for each vertex of the input.
• Vertices are assembled into primitives.
• Optionally, a shader named the tessellation control shader is run once for each primitive and indicates the tessellation level to apply for this primitive.
• Optionally, a shader named the tessellation evaluation shader is run once for each vertex, including the ones newly created by the tessellation.
• Optionally, a shader named the geometry shader is run once for each line or triangle.
• The vertex coordinates (as outputted by the geometry shader, or by the tessellation evaluation shader if there's no geometry shader, or by the vertex shader if there's no geometry shader nor tessellation evaluation shader) are turned into screen-space coordinates.
• The list of pixels that cover each triangle are determined.
• A shader named the fragment shader is run once for each pixel that covers one of the triangles.
• The depth test and/or the stencil test are performed.
• The output of the fragment shader is written to the framebuffer attachments, possibly by mixing it with the existing values.

All the sub-modules of this module (with the exception of cache) correspond to the various stages of graphical pipelines.

Note: With the exception of the addition of the tessellation shaders and the geometry shader, these steps haven't changed in the past decade. If you are familiar with shaders in OpenGL 2 for example, don't worry as it works in the same in Vulkan.

Note: All the stages that consist in executing a shader are performed by a microprocessor (unless you happen to use a software implementation of Vulkan). As for the other stages, some hardware (usually desktop graphics cards) have dedicated chips that will execute them while some other hardware (usually mobile) perform them with the microprocessor as well. In the latter situation, the implementation will usually glue these steps to your shaders.

Creating a graphics pipeline follows the same principle as a compute pipeline, except that you must pass multiple shaders alongside with configuration for the other steps.

TODO: add an example

Modules

blend	Defines how the color output of the fragment shader is written to the attachment.
cache	Cache the pipeline objects to disk for faster reloads.
depth_stencil	Depth and stencil operations description.
input_assembly	Assembling vertices into primitives.
multisample	State of multisampling.
raster	Stage when triangles are turned into pixels.
shader	Stage of a graphics pipeline.
vertex	Vertex sources definition
viewport	Viewports and scissor boxes.

Structs

ComputePipeline	A pipeline object that describes to the Vulkan implementation how it should perform compute operations.
ComputePipelineSys	Opaque object that represents the inside of the compute pipeline. Can be made into a trait object.
GraphicsPipeline	Defines how the implementation should perform a draw operation.
GraphicsPipelineBuilder	Prototype for a GraphicsPipeline.
GraphicsPipelineSys	Opaque object that represents the inside of the graphics pipeline.

Enums

ComputePipelineCreationError	Error that can happen when creating a compute pipeline.
GraphicsPipelineCreationError	Error that can happen when creating a graphics pipeline.

Traits

ComputePipelineAbstract	Trait implemented on all compute pipelines.
GraphicsPipelineAbstract	Trait implemented on objects that reference a graphics pipeline. Can be made into a trait object. When using this trait AutoCommandBufferBuilder::draw* calls will need the buffers to be wrapped in a vec!().