VK_QCOM_filter_cubic_clamp

Other Extension Metadata

Last Modified Date

2023-08-02

Contributors

• Jeff Leger, Qualcomm Technologies, Inc.

Description

This extension extends cubic filtering by adding the ability to enable an anti-ringing clamp. Cubic filtering samples from a 4x4 region of texels and computes a cubic weighted average of the region. In some cases, the resulting value is outside the range of any of the texels in the 4x4 region. This is sometimes referred to as filter overshoot or filter ringing and can occur when there is a sharp discontinuity in the 4x4 region being filtered. For some use cases this ringing can produces unacceptable artifacts.

The solution to the ringing problem is to clamp the post-cubic-filtered value to be within the max and min of texel values in the 4x4 region. While such range clamping can be performed in shader code, the additional texture fetches and clamping ALU operations can be costly.

Certain Adreno GPUs are able to perform the range clamp in the texture unit during cubic filtering at significant performance/power savings versus a shader-based clamping approach. This extension exposes such hardware functionality.

This extension extends VkSamplerReductionMode, adding VK_SAMPLER_REDUCTION_MODE_WEIGHTED_AVERAGE_RANGECLAMP_QCOM which enables the range clamp operation.

New Structures

• Extending VkPhysicalDeviceFeatures2, VkDeviceCreateInfo:
  • VkPhysicalDeviceCubicClampFeaturesQCOM

New Enum Constants

• VK_QCOM_FILTER_CUBIC_CLAMP_EXTENSION_NAME
• VK_QCOM_FILTER_CUBIC_CLAMP_SPEC_VERSION
• Extending VkSamplerReductionMode:
  • VK_SAMPLER_REDUCTION_MODE_WEIGHTED_AVERAGE_RANGECLAMP_QCOM
• Extending VkStructureType:
  • VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_CUBIC_CLAMP_FEATURES_QCOM

Version History

• Revision 1, 2023-08-02 (jleger)
  • Initial version