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src/libANGLE/renderer/vulkan/shaders/README.md

Shader Variations

To build multiple variations of a shader, add a file named X.json corresponding to shader file X. A variation is generated by building the shader with different definitions (a la glslang_validator's -DName=1). These definitions come from flags and enumerations defined in the json file. Without a .json file, the shader is generated as is (1 variation).

There are multiple possible fields in the json file:

  • “Description”: This contains the license and other comments, which will be ignored.
  • “Flags”: this is a list of flags. Each flag FLAG defines a shader variation with or without the define FLAG=1.
  • other: any other field is a similar list to flags, except that each entry in this enumeration is a variation. Similar to “flags”, every entry ENTRY results in an ENTRY=1 define.

Flags are shorthand for 2-entry enumerations. Given n flags, there are 2^n variations where every flag is either present or not. For enumerations, only one entry is active in any variation. Thus, an enumeration with n entries generates n variations.

Example

Here is an example json file:

{ “Description”: [ “Copyright 2018 The ANGLE Project Authors. All rights reserved.”, “Use of this source code is governed by a BSD-style license that can be”, “found in the LICENSE file.”, "", “RayTrace.comp.json: Build parameters for RayTrace.comp.” ], “Flags”: [ “NanFilter”, “WorkaroundIntelBug” ], “RayTraceQuality”: [ “IsRTLowRes”, “IsRTHighRes”, “IsRTAwesome” ], “ImageType”: [ “IsR”, “IsRG”, “IsRGB”, “IsRGBA” ] }

This will generate 2^2 * 3 * 4 shaders.