VK_KHR_sampler_mirror_clamp_to_edge

Other Extension Metadata

Last Modified Date

2019-08-17

Contributors

Tobias Hector, Imagination Technologies
Jon Leech, Khronos

VK_KHR_sampler_mirror_clamp_to_edge extends the set of sampler address modes to include an additional mode (VK_SAMPLER_ADDRESS_MODE_MIRROR_CLAMP_TO_EDGE) that effectively uses a texture map twice as large as the original image in which the additional half of the new image is a mirror image of the original image.

This new mode relaxes the need to generate images whose opposite edges match by using the original image to generate a matching mirror image. This mode allows the texture to be mirrored only once in the negative s, t, and r directions.

Promotion to Vulkan 1.2

All functionality in this extension is included in core Vulkan 1.2. However, if Vulkan 1.2 is supported and this extension is not, the VkSamplerAddressMode

VK_SAMPLER_ADDRESS_MODE_MIRROR_CLAMP_TO_EDGE is optional. Since the original extension did not use an author suffix on the enum VK_SAMPLER_ADDRESS_MODE_MIRROR_CLAMP_TO_EDGE, it is used by both core and extension implementations.

New Enum Constants

VK_KHR_SAMPLER_MIRROR_CLAMP_TO_EDGE_EXTENSION_NAME
VK_KHR_SAMPLER_MIRROR_CLAMP_TO_EDGE_SPEC_VERSION
Extending VkSamplerAddressMode:
- VK_SAMPLER_ADDRESS_MODE_MIRROR_CLAMP_TO_EDGE
- VK_SAMPLER_ADDRESS_MODE_MIRROR_CLAMP_TO_EDGE_KHR

Example

Creating a sampler with the new address mode in each dimension

    VkSamplerCreateInfo createInfo =
    {
        .sType = VK_STRUCTURE_TYPE_SAMPLER_CREATE_INFO,
        // Other members set to application-desired values
    };

    createInfo.addressModeU = VK_SAMPLER_ADDRESS_MODE_MIRROR_CLAMP_TO_EDGE;
    createInfo.addressModeV = VK_SAMPLER_ADDRESS_MODE_MIRROR_CLAMP_TO_EDGE;
    createInfo.addressModeW = VK_SAMPLER_ADDRESS_MODE_MIRROR_CLAMP_TO_EDGE;

    VkSampler sampler;
    VkResult result = vkCreateSampler(
        device,
        &createInfo,
        &sampler);

Issues

1) Why are both KHR and core versions of the VK_SAMPLER_ADDRESS_MODE_MIRROR_CLAMP_TO_EDGE token present?

RESOLVED: This functionality was intended to be required in Vulkan 1.0. We realized shortly before public release that not all implementations could support it, and moved the functionality into an optional extension, but did not apply the KHR extension suffix. Adding a KHR-suffixed alias of the non-suffixed enum has been done to comply with our own naming rules.

In a related change, before spec revision 1.1.121 this extension was hardwiring into the spec Makefile so it was always included with the Specification, even in the core-only versions. This has now been reverted, and it is treated as any other extension.

Version History

Revision 1, 2016-02-16 (Tobias Hector)
- Initial draft
Revision 2, 2019-08-14 (Jon Leech)
- Add KHR-suffixed alias of non-suffixed enum.
Revision 3, 2019-08-17 (Jon Leech)
- Add an issue explaining the reason for the extension API not being suffixed with KHR.