KhronosGroup/MoltenVK

Add support for VkLogicOp

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#374 opened on Dec 8, 2018

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EnhancementHelp wanted

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Description

MoltenVK currently does not support the VkLogicOp member of the VkPipelineColorBlendStateCreateInfo structure, for the understandable reason that Metal has no equivalent functionality. However I make extensive use of AND, OR and XOR logical operations in my applications and the loss of this feature would be a very serious problem for me (currently I am using glLogicOp in OpenGL and hoping Apple doesn't drop OpenGL support in MacOS any time soon!).

It has been suggested that a workaround might be possible in MoltenVK by implementing the logical operations in a shader, is this something on the radar?

Contributor guide

Research direction
Investigate implementing VkLogicOp by emulating logical operations in the fragment shader using bitwise operations. This would require intercepting the pipeline creation and replacing the shader with one that performs the logical operation. Alternatively, consider using texture barriers and pixel formats to achieve logical operations on Metal.
Tech stack
objective cccpp
Domain
computer graphics
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
VulkanMetalGPU programming
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30