The viewport transformation is determined by the selected viewport’s width and height in pixels, px and py, respectively, and its center (ox, oy) (also in pixels), as well as its depth range min and max determining a depth range scale value pz and a depth range bias value oz (defined below). The vertex’s framebuffer coordinates (xf, yf, zf) are given by
Multiple viewports are available, numbered zero up to
VkPhysicalDeviceLimits::maxViewports minus one.
The number of viewports used by a pipeline is controlled by the
viewportCount member of the VkPipelineViewportStateCreateInfo
structure used in pipeline creation.
The VkPipelineViewportStateCreateInfo structure is defined as:
typedef struct VkPipelineViewportStateCreateInfo {
VkStructureType sType;
const void* pNext;
VkPipelineViewportStateCreateFlags flags;
uint32_t viewportCount;
const VkViewport* pViewports;
uint32_t scissorCount;
const VkRect2D* pScissors;
} VkPipelineViewportStateCreateInfo;
sType is the type of this structure.
pNext is NULL or a pointer to an extension-specific structure.
flags is reserved for future use.
viewportCount is the number of viewports used by the pipeline.
pViewports is a pointer to an array of VkViewport
structures, defining the viewport transforms.
If the viewport state is dynamic, this member is ignored.
scissorCount is the number of scissors and
must match the number of viewports.
pScissors is a pointer to an array of VkRect2D structures
which define the rectangular bounds of the scissor for the corresponding
viewport.
If the scissor state is dynamic, this member is ignored.
If a geometry shader is active and has an output variable decorated with
ViewportIndex, the viewport transformation uses the viewport
corresponding to the value assigned to ViewportIndex taken from an
implementation-dependent vertex of each primitive.
If ViewportIndex is outside the range zero to viewportCount minus
one for a primitive, or if the geometry shader did not assign a value to
ViewportIndex for all vertices of a primitive due to flow control, the
results of the viewport transformation of the vertices of such primitives
are undefined.
If no geometry shader is active, or if the geometry shader does not have an
output decorated with ViewportIndex, the viewport numbered zero is used
by the viewport transformation.
A single vertex can be used in more than one individual primitive, in
primitives such as VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP.
In this case, the viewport transformation is applied separately for each
primitive.
If the bound pipeline state object was not created with the
VK_DYNAMIC_STATE_VIEWPORT dynamic state enabled, viewport
transformation parameters are specified using the pViewports member of
VkPipelineViewportStateCreateInfo in the pipeline state object.
If the pipeline state object was created with the
VK_DYNAMIC_STATE_VIEWPORT dynamic state enabled, the viewport
transformation parameters are dynamically set and changed with the command:
void vkCmdSetViewport(
VkCommandBuffer commandBuffer,
uint32_t firstViewport,
uint32_t viewportCount,
const VkViewport* pViewports);
commandBuffer is the command buffer into which the command will be
recorded.
firstViewport is the index of the first viewport whose parameters
are updated by the command.
viewportCount is the number of viewports whose parameters are
updated by the command.
pViewports is a pointer to an array of VkViewport structures
specifying viewport parameters.
The viewport parameters taken from element i of pViewports
replace the current state for the viewport index firstViewport
+ i, for i in [0, viewportCount).
Both VkPipelineViewportStateCreateInfo and vkCmdSetViewport use
VkViewport to set the viewport transformation parameters.
The VkViewport structure is defined as:
typedef struct VkViewport {
float x;
float y;
float width;
float height;
float minDepth;
float maxDepth;
} VkViewport;
x and y are the viewport’s upper left corner (x,y).
width and height are the viewport’s width and height,
respectively.
minDepth and maxDepth are the depth range for the viewport.
It is valid for minDepth to be greater than or equal to
maxDepth.
The framebuffer depth coordinate zf may be represented using
either a fixed-point or floating-point representation.
However, a floating-point representation must be used if the depth/stencil
attachment has a floating-point depth component.
If an m-bit fixed-point representation is used, we assume that it
represents each value
$\frac{k}{2^m - 1}$
, where k ∈ {
0, 1, …, 2m-1 }, as k (e.g. 1.0 is represented in binary as a
string of all ones).
The viewport parameters shown in the above equations are found from these values as
x + width / 2
y + height / 2
minDepth
width
height
maxDepth - minDepth.
The width and height of the implementation-dependent maximum viewport dimensions must be greater than or equal to the width and height of the largest image which can be created and attached to a framebuffer.
The floating-point viewport bounds are represented with an implementation-dependent precision.