Vulkan Terminology

Instance

Connection between your application and the Vulkan library

Typically your application will only create one

Every other Vulkan call relies on passing this instance or some data associated with this instance

Context

Vulkan instance is similar to an OpenGL context

Context is not a term used in the Vulkan API

Surface

A term for the window region where images are rendered

Native window support is not handled directly in the API, it is implemented in platform extensions

Memory Heap

Provides storage for buffers which will be accessed by the GPU

Every buffer must be created and managed by the user

Memory is allocated from a memory heap

The buffer is then bound to the allocated memory

Any memory which is visible to the GPU will be in the list of all memory heaps

There are usually multiple heaps available

Certain heaps can only be used for specific types of buffers

Vertex Buffer

Coordinates of all vertices which describes the geometry for the image being rendered

Triangles are the most widely used shape

There can be as few as three vertices, typically thousands for a given image

Uniform Buffer

Contains data which is applied to every vertex

For example, transformations can be used to shift the geometry and render the image somewhere other than the center

Vertex Shader

Transforms a 3D position into 2D coordinates

Executes once per vertex

Tessellation Shader

Decomposes shapes into smaller components, optional shader

Geometry Shader

Alters the vertex shader output, optional shader

Fragment Shader

uses lighting and textures to calculate colors

executes at least once per pixel or fragment (partial pixel)

Pipeline

Before a draw command is added to a command buffer you must create a pipeline object which sets a whole lot of options

Shader handles, descriptor sets, push constants, depth buffer

Winding direction, culling options, viewport

Stencil, scissor, blending

Command Buffer

Accumulates draw commands which are executed on the GPU at a later time

Only way to synchronize these commands is by using a barrier

• Set semaphore, query semaphore
• Wait for pipeline stage (such as wait for a vertex shader to finish)

Frame Buffer

Typically contains one image

No default buffer exists since displaying an image is optional

A frame buffer us not required if no images are displayed

Depth Buffer

A 3D mesh has perspective and to draw it realistically some triangles must appear in front of other triangles

A depth buffer is used to determine what part of the mesh is closer to the camera

Misconfiguring this buffer will result in far away objects being rendered on top of closer objects

Render Pass

Added for improved performance on mobile

• OpenGL and DirectX 12 do not have a render pass equivalent

For tile based GPU support

• common in mobile, uncommon on desktop computers

A pipeline needs information about color channels, the depth buffer, possible image sampling, etc

All of this information is split into one or more render passes

begin command buffer, begin render pass

add commands for this one pass

end render pass, end command buffer

Swapchain

A set of buffers where the GPU can render

In Vulkan there is no default frame buffer

Creating a swapchain is the only way to create an empty frame buffer

Each frame buffer will hold a single image which is waiting to be presented on the surface

A single swap chain can contain many frame buffers

Platform specific, supplied through “extensions” which are requested when you create the Vulkan instance

Graphics Queue

Used to generate an image

Present Queue

Used to copy images to the screen

Computation Queue

Used to run general purpose computations

Transfer Queue

Used to copy data between CPU memory and GPU memory

Fence

Used to synchronize work between the CPU and the GPU

Status of a fence can be accessed from your program

Semaphore

Used to synchronize work occurring on the GPU

Semaphore dependencies are set up in your program however they are observed only on the GPU

Not visible to the CPU nor can you query their status

Winding Direction

Must be specified as part of the pipeline

Conventionally clockwise winding is used

The direction is used to determine whether a given triangle is facing the camera (front facing) or facing away (back facing)

Back Face Culling

Is the process of discarding triangles which are back facing since these are not normally visible to the viewer

There is no default so it must be set on or off in the pipeline

Triangles are "culled" early in the rendering pipeline

Increases efficiency by reducing the number of fragments which are processed

Push Constants

A way to provide a small amount of uniform data to shaders

Scissor

Scissor test restricts drawing to the specified rectangle

Test is always enabled and can not be turned off

Extent

Structure containing width and height

Defines things like the size of the screen or the render area

Viewport

Specifies a region of the frame buffer which should be refreshed, potentially complicated to determine