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.