Contact
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Eric Werness [GitHub]ewerness-nv
Other Extension Metadata
- Last Modified Date
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2017-02-15
- Contributors
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Eric Werness, NVIDIA
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Kedarnath Thangudu, NVIDIA
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Description
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.
New Enum Constants
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VK_NV_CLIP_SPACE_W_SCALING_EXTENSION_NAME -
VK_NV_CLIP_SPACE_W_SCALING_SPEC_VERSION -
Extending VkDynamicState:
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Extending VkStructureType:
Issues
1) Is the pipeline structure name too long?
RESOLVED: It fits with the naming convention.
2) Separate W scaling section or fold into coordinate transformations?
RESOLVED: Leaving it as its own section for now.
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);
}Document Notes
For more information, see the Vulkan Specification.
This page is a generated document. Fixes and changes should be made to the generator scripts, not directly.