1// Copyright 2021-2024 The Khronos Group Inc. 2// 3// SPDX-License-Identifier: CC-BY-4.0 4 5include::{generated}/meta/{refprefix}VK_EXT_depth_clip_control.adoc[] 6 7=== Other Extension Metadata 8 9*Last Modified Date*:: 10 2021-11-09 11*Contributors*:: 12 - Spencer Fricke, Samsung Electronics 13 - Shahbaz Youssefi, Google 14 - Ralph Potter, Samsung Electronics 15 16=== Description 17 18This extension allows the application to use the OpenGL depth range in NDC, 19i.e. with depth in range [eq]#[-1, 1]#, as opposed to Vulkan's default of 20[eq]#[0, 1]#. 21The purpose of this extension is to allow efficient layering of OpenGL over 22Vulkan, by avoiding emulation in the pre-rasterization shader stages. 23This emulation, which effectively duplicates gl_Position but with a 24different depth value, costs ALU and consumes shader output components that 25the implementation may not have to spare to meet OpenGL minimum 26requirements. 27 28include::{generated}/interfaces/VK_EXT_depth_clip_control.adoc[] 29 30=== Issues 31 321) Should this extension include an origin control option to match 33GL_LOWER_LEFT found in ARB_clip_control? 34 35*RESOLVED*: No. 36The fix for porting over the origin is a simple y-axis flip. 37The depth clip control is a much harder problem to solve than what this 38extension is aimed to solve. 39Adding an equivalent to GL_LOWER_LEFT would require more testing. 40 412) Should this pipeline state be dynamic? 42 43*RESOLVED*: Yes. 44The purpose of this extension is to emulate the OpenGL depth range, which is 45expected to be globally fixed (in case of OpenGL ES) or very infrequently 46changed (with `glClipControl` in OpenGL). 47 483) Should the control provided in this extension be an enum that could be 49extended in the future? 50 51*RESOLVED*: No. 52It is highly unlikely that the depth range is changed to anything other than 53[eq]#[0, 1]# in the future. 54Should that happen a new extension will be required to extend such an enum, 55and that extension might as well add a new struct to chain to 56slink:VkPipelineViewportStateCreateInfo::pname:pNext instead. 57 58=== Version History 59 60 * Revision 0, 2020-10-01 (Spencer Fricke) 61 ** Internal revisions 62 63 * Revision 1, 2020-11-26 (Shahbaz Youssefi) 64 ** Language fixes 65 66