Package org.lwjgl.vulkan

Class NVClipSpaceWScaling

java.lang.Object

org.lwjgl.vulkan.NVClipSpaceWScaling

public class NVClipSpaceWScaling
extends Object

Virtual Reality (VR) applications often involve a post-processing step to apply a “barrel” distortion to the rendered image to correct the “pincushion” distortion introduced by the optics in a VR device. The barrel distorted image has lower resolution along the edges compared to the center. Since the original image is rendered at high resolution, which is uniform across the complete image, a lot of pixels towards the edges do not make it to the final post-processed image.

This extension provides a mechanism to render VR scenes at a non-uniform resolution, in particular a resolution that falls linearly from the center towards the edges. This is achieved by scaling the w coordinate of the vertices in the clip space before perspective divide. The clip space w coordinate of the vertices can be offset as of a function of x and y coordinates as follows:

w' = w + Ax + By

In the intended use case for viewport position scaling, an application should use a set of four viewports, one for each of the four quadrants of a Cartesian coordinate system. Each viewport is set to the dimension of the image, but is scissored to the quadrant it represents. The application should specify A and B coefficients of the w-scaling equation above, that have the same value, but different signs, for each of the viewports. The signs of A and B should match the signs of x and y for the quadrant that they represent such that the value of w' will always be greater than or equal to the original w value for the entire image. Since the offset to w, (Ax + By), is always positive, and increases with the absolute values of x and y, the effective resolution will fall off linearly from the center of the image to its edges.

Examples

 VkViewport viewports[4];
 VkRect2D scissors[4];
 VkViewportWScalingNV scalings[4];
 
 for (int i = 0; i < 4; i++) {
     int x = (i & 2) ? 0 : currentWindowWidth / 2;
     int y = (i & 1) ? 0 : currentWindowHeight / 2;
 
     viewports[i].x = 0;
     viewports[i].y = 0;
     viewports[i].width = currentWindowWidth;
     viewports[i].height = currentWindowHeight;
     viewports[i].minDepth = 0.0f;
     viewports[i].maxDepth = 1.0f;
 
     scissors[i].offset.x = x;
     scissors[i].offset.y = y;
     scissors[i].extent.width = currentWindowWidth/2;
     scissors[i].extent.height = currentWindowHeight/2;
 
     const float factor = 0.15;
     scalings[i].xcoeff = ((i & 2) ? -1.0 : 1.0) * factor;
     scalings[i].ycoeff = ((i & 1) ? -1.0 : 1.0) * factor;
 }
 
 VkPipelineViewportWScalingStateCreateInfoNV vpWScalingStateInfo = { VK_STRUCTURE_TYPE_PIPELINE_VIEWPORT_W_SCALING_STATE_CREATE_INFO_NV };
 
 vpWScalingStateInfo.viewportWScalingEnable = VK_TRUE;
 vpWScalingStateInfo.viewportCount = 4;
 vpWScalingStateInfo.pViewportWScalings = &scalings[0];
 
 VkPipelineViewportStateCreateInfo vpStateInfo = { VK_STRUCTURE_TYPE_PIPELINE_VIEWPORT_STATE_CREATE_INFO };
 vpStateInfo.viewportCount = 4;
 vpStateInfo.pViewports = &viewports[0];
 vpStateInfo.scissorCount = 4;
 vpStateInfo.pScissors = &scissors[0];
 vpStateInfo.pNext = &vpWScalingStateInfo;

Example shader to read from a w-scaled texture:

 // Vertex Shader
 // Draw a triangle that covers the whole screen
 const vec4 positions[3] = vec4[3](vec4(-1, -1, 0, 1),
                                   vec4( 3, -1, 0, 1),
                                   vec4(-1,  3, 0, 1));
 out vec2 uv;
 void main()
 {
     vec4 pos = positions[ gl_VertexID ];
     gl_Position = pos;
     uv = pos.xy;
 }
 
 // Fragment Shader
 uniform sampler2D tex;
 uniform float xcoeff;
 uniform float ycoeff;
 out vec4 Color;
 in vec2 uv;
 
 void main()
 {
     // Handle uv as if upper right quadrant
     vec2 uvabs = abs(uv);
 
     // unscale: transform w-scaled image into an unscaled image
     //   scale: transform unscaled image int a w-scaled image
     float unscale = 1.0 / (1 + xcoeff * uvabs.x + xcoeff * uvabs.y);
     //float scale = 1.0 / (1 - xcoeff * uvabs.x - xcoeff * uvabs.y);
 
     vec2 P = vec2(unscale * uvabs.x, unscale * uvabs.y);
 
     // Go back to the right quadrant
     P *= sign(uv);
 
     Color = texture(tex, P * 0.5 + 0.5);
 }

VK_NV_clip_space_w_scaling

Name String

VK_NV_clip_space_w_scaling

Extension Type

Device extension

Registered Extension Number

88

Revision

1

Contact

• Eric Werness ewerness-nv

Other Extension Metadata

Last Modified Date

2017-02-15

Contributors

• Eric Werness, NVIDIA
• Kedarnath Thangudu, NVIDIA

Field Summary

Fields

Modifier and Type	Field	Description
static final int	VK_DYNAMIC_STATE_VIEWPORT_W_SCALING_NV	Extends VkDynamicState.
static final String	VK_NV_CLIP_SPACE_W_SCALING_EXTENSION_NAME	The extension name.
static final int	VK_NV_CLIP_SPACE_W_SCALING_SPEC_VERSION	The extension specification version.
static final int	VK_STRUCTURE_TYPE_PIPELINE_VIEWPORT_W_SCALING_STATE_CREATE_INFO_NV	Extends VkStructureType.

Method Summary

Modifier and Type	Method	Description
static void	nvkCmdSetViewportWScalingNV(VkCommandBuffer commandBuffer, int firstViewport, int viewportCount, long pViewportWScalings)	Unsafe version of: CmdSetViewportWScalingNV
static void	vkCmdSetViewportWScalingNV(VkCommandBuffer commandBuffer, int firstViewport, VkViewportWScalingNV.Buffer pViewportWScalings)	Set the viewport W scaling dynamically for a command buffer.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

VK_NV_CLIP_SPACE_W_SCALING_SPEC_VERSION

public static final int VK_NV_CLIP_SPACE_W_SCALING_SPEC_VERSION

The extension specification version.

See Also:

• Constant Field Values

VK_NV_CLIP_SPACE_W_SCALING_EXTENSION_NAME

public static final String VK_NV_CLIP_SPACE_W_SCALING_EXTENSION_NAME

The extension name.

See Also:

• Constant Field Values

VK_STRUCTURE_TYPE_PIPELINE_VIEWPORT_W_SCALING_STATE_CREATE_INFO_NV

public static final int VK_STRUCTURE_TYPE_PIPELINE_VIEWPORT_W_SCALING_STATE_CREATE_INFO_NV

Extends VkStructureType.

See Also:

• Constant Field Values

VK_DYNAMIC_STATE_VIEWPORT_W_SCALING_NV

public static final int VK_DYNAMIC_STATE_VIEWPORT_W_SCALING_NV

Extends VkDynamicState.

See Also:

• Constant Field Values

Method Details

nvkCmdSetViewportWScalingNV

public static void nvkCmdSetViewportWScalingNV(VkCommandBuffer commandBuffer,
 int firstViewport,
 int viewportCount,
 long pViewportWScalings)

Unsafe version of: CmdSetViewportWScalingNV

Parameters:

viewportCount - the number of viewports whose parameters are updated by the command.

vkCmdSetViewportWScalingNV

public static void vkCmdSetViewportWScalingNV(VkCommandBuffer commandBuffer,
 int firstViewport,
 VkViewportWScalingNV.Buffer pViewportWScalings)

Set the viewport W scaling dynamically for a command buffer.

C Specification

To dynamically set the viewport W scaling parameters, call:

 void vkCmdSetViewportWScalingNV(
     VkCommandBuffer                             commandBuffer,
     uint32_t                                    firstViewport,
     uint32_t                                    viewportCount,
     const VkViewportWScalingNV*                 pViewportWScalings);

Description

The viewport parameters taken from element i of pViewportWScalings replace the current state for the viewport index firstViewport + i, for i in [0, viewportCount).

This command sets the viewport W scaling for subsequent drawing commands when drawing using shader objects, or when the graphics pipeline is created with DYNAMIC_STATE_VIEWPORT_W_SCALING_NV set in VkPipelineDynamicStateCreateInfo::pDynamicStates. Otherwise, this state is specified by the VkPipelineViewportWScalingStateCreateInfoNV::pViewportWScalings values used to create the currently active pipeline.

Valid Usage

• The sum of firstViewport and viewportCount must be between 1 and VkPhysicalDeviceLimits::maxViewports, inclusive

Valid Usage (Implicit)

• commandBuffer must be a valid VkCommandBuffer handle
• pViewportWScalings must be a valid pointer to an array of viewportCount VkViewportWScalingNV structures
• commandBuffer must be in the recording state
• The VkCommandPool that commandBuffer was allocated from must support graphics operations
• This command must only be called outside of a video coding scope
• viewportCount must be greater than 0

Host Synchronization

• Host access to commandBuffer must be externally synchronized
• Host access to the VkCommandPool that commandBuffer was allocated from must be externally synchronized

Command Properties

Command Buffer Levels	Render Pass Scope	Video Coding Scope	Supported Queue Types	Command Type
Primary Secondary	Both	Outside	Graphics	State

See Also

VkViewportWScalingNV

Parameters:

commandBuffer - the command buffer into which the command will be recorded.

firstViewport - the index of the first viewport whose parameters are updated by the command.

pViewportWScalings - a pointer to an array of VkViewportWScalingNV structures specifying viewport parameters.