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Shader Minifier

Shader Minifier is a tool that minifies and obfuscates shader code (GLSL and HLSL) without affecting its behaviour. It is also suitable for reducing the size of the shaders in other applications (e.g. webgl, games).

Its original use-case is for the demoscene, for optimizing 4k and 64k intros. In the context of 4kB intros, Shader Minifier help developers maintain and iterate on human-readable files, while shipping optimized code. Even when a shader is minified by hand by experienced demosceners, Shader Minifier is often able to optimize it further. See this 2010 report.

Shader Minifier is available:

• As an online website: https://ctrl-alt-test.fr/minifier/
• As a command-line tool (download from Releases)
• As a .NET library (see Example)

To be notified of new releases, use the watch feature of GitHub.

Features

• Parsing and printing of GLSL or HLSL code.
• Generation of a file (such as a C header) that can be embedded in an application.
• A command-line interface that can fit in a build.
• A web interface, for interactive workflows.
• Ability to minify multiple shaders at once, in a consistent way.

See the list of transformations for more information. In brief:

• Strip spaces, remove comments, remove useless parens.
• Inline functions, variables and constant values.
• Simplify constant expressions: 5. * 2. becomes 10..
• Group declarations: float a=2.;float b; becomes float a=2.,b;.
• Apply other tricks to reduce the file size.
• Simplify calls to vector constructors using vector swizzles.
• Rename variables, typically to one character.
• Remove unused local variables, unused functions and other dead code.

Other transformations try to make the code more compression friendly, e.g.

• Consistently rename vector fields (e.g. use foo.xy instead of foo.rg) to help the compression.
• Reuse the variable names as much as possible: a local variable may have the same name as a global variable not used in the function; two functions may have the same name using function overloading.
• Analyze the context and make statistics to compute the variable name that will be the most compression-friendly.

Example output

/* File generated with Shader Minifier 1.3
 * http://www.ctrl-alt-test.fr
 */
#ifndef HEART_FRAG_EXPECTED_
# define HEART_FRAG_EXPECTED_
# define VAR_mouse "f"
# define VAR_resolution "y"
# define VAR_time "v"

const char *heart_frag =
 "uniform float v;"
 "uniform vec2 y;"
 "uniform vec4 f;"
 "void main()"
 "{"
   "vec2 f=(2.*gl_FragCoord.xy-y)/y.y;"
   "float r=mod(v,2.)/2.,a=pow(r,.2)*.5+.5;"
   "a-=a*.2*sin(r*6.2831*5.)*exp(-r*6.);"
   "f*=vec2(.5,1.5)+a*vec2(.5,-.5);"
   "float m=atan(f.x,f.y)/3.141593,x=length(f),e=abs(m),o=(13.*e-22.*e*e+10.*e*e*e)/(6.-5.*e),n=step(x,o)*pow(1.-x/o,.25);"
   "gl_FragColor=vec4(n,0.,0.,1.);"
 "}";

#endif // HEART_FRAG_EXPECTED_

Multiple output formats are available.

Usage

Download Shader Minifier here: https://github.com/laurentlb/Shader_Minifier/releases

It is a command-line tool. Without argument, it will show the usage. If you are not on Windows, you will need mono:

$ shader_minifier.exe  # Windows
$ mono shader_minifier.exe  # Linux, Mac...

USAGE: Shader Minifier [--help] [-o <string>] [-v] [--hlsl]
                       [--format <text|indented|c-variables|c-array|js|nasm|rust>]
                       [--field-names <rgba|xyzw|stpq>] [--preserve-externals]
                       [--preserve-all-globals] [--no-inlining]
                       [--aggressive-inlining] [--no-renaming]
                       [--no-renaming-list <string>] [--no-sequence]
                       [--no-remove-unused]
                       [--move-declarations] [<filename>...]

FILENAMES:

    <filename>...         List of files to minify

OPTIONS:

    -o <string>           Set the output filename (default is shader_code.h)
    -v                    Verbose, display additional information
    --hlsl                Use HLSL (default is GLSL)
    --format <text|indented|c-variables|c-array|js|nasm|rust>
                          Choose to format the output (use 'text' if you want
                          just the shader)
    --field-names <rgba|xyzw|stpq>
                          Choose the field names for vectors: 'rgba', 'xyzw',
                          or 'stpq'
    --preserve-externals  Do not rename external values (e.g. uniform)
    --preserve-all-globals
                          Do not rename functions and global variables
    --no-inlining         Do not automatically inline variables, functions
                          and arguments
    --aggressive-inlining Aggressively inline constants. This can reduce output
                          size due to better constant folding. It can also
                          increase output size due to repeated inlined
                          constants, but this increased redundancy can be
                          beneficial to compression, leading to a smaller final
                          compressed size anyway. Does nothing if inlining is
                          disabled.
    --no-renaming         Do not rename anything
    --no-renaming-list <string>
                          Comma-separated list of functions to preserve
    --no-sequence         Do not use the comma operator trick
    --no-remove-unused    Do not remove unused code
    --move-declarations   Move declarations to group them
    --preprocess          Evaluate some of the file preprocessor directives
    --export-kkp-symbol-maps
                          Export kkpView symbol maps
    --help                display this list of options.

In short:

• List the shaders you want to minify on the command-line.

• Use -o to choose the output file (by default, it will use shader_code.h). If you pass - for the output, it will be printed on stdout.

• Use --format to control the output format. By default, it will create a C header. There are other options to get only the shader, or have it in a Javascript, Rust, or nasm file.

Tips

4kB intros

4kB intros typically use a single shader file. The default flags should work well:

shader_minifier.exe -o shader_code.h fragment.glsl

We recommend that you frequently check the output of Shader Minifier to make sure there are no obvious problems. Use inlining where possible.

If you desperately need to save a few bytes, try another value of --field-names. It can affect the size after compression.

64kB intros

The recommandation is to use:

shader_minifier.exe --format c-array *.frag -o shaders.h

Then, in your C or C++ code, include the file:

const char* shaderSources[] = {
#define SHADER_MINIFIER_IMPL
#include shaders.h
};

Note that uniforms will be renamed consistently across all the files. The #define lines will tell you how they were renamed. To disable this renaming, use --preserve-externals.

Javascript

Use --format js. It will define a variable for each shader, the variable name being derived from the input file. We expect you to run a Javascript minifier on the output file.

Other applications

The simplest solution is to minify each file separately:

shader_minifier.exe --format text --preserve-externals file.glsl -o file_opt.glsl

The output may be used as a drop-in replacement for your original shaders.

Debugging

To better understand what Shader Minifier changed and get a more readable output, use the flags --format indented --no-renaming. This will add some indentation to the output, instead of using overly long lines.

Concepts

Shader behaviour

Shader Minifer works by applying to the AST modifications that produce a transformed but semantically equivalent AST. The resulting assembly may be different, but the minified shader should have the same behaviour as the original one. Or at least that's the intent.

Some of the transformations are not completely safe and may break in some corner cases. If you observe differences, don't hesitate to report a bug.

Macros

Shader Minifier will preserve the preprocessor directives (the lines starting with #), except that it strips the spaces.

If you define a macro, Shader Minifier will notice the name of the macro and won't rename the occurrences of the macro. It also doesn't rename variables used inside the macro. Clever macros are discouraged and can break the shader.

Avoid macros that contain references to other variables, or affect how the code should be parsed. You may get a parse error in Shader Minifier, or get an output that won't compile.

Evaluation of preprocessor directives

With the flag --preprocess, Shader Minifier will try to evaluate some preprocessing directives:

• #ifdef is evaluated based on macros defined in the file.
• #else is supported.
• Nested #ifdef are supported.
• Unknown directives will be preserved.

This is still experimental and there are some limitations:

• Macros declared with #define will be kept in the file, even if they are no longer needed.
• #define and #undefine that appear inside a #if region are not well handled.

Verbatim

If you want to temporary turn off the minifier, use the //[ and //] comments. This can be useful as a workaround if you get a parser error.

Variables inside the region won't be renamed. Spaces will be stripped.

//[
layout(local_size_x = 32) in;
//]

Overloading

At this time, do not use overloaded functions (two functions with the same name but different arguments) in the input. The output probably won't compile.

On the other hand, Shader Minifier will aggressively use function overloading in the output. If two functions have a different number of arguments, they may have the same name in the output. This reduces the number of identifiers used by the shader and make it more compression friendly.

kkpView symbol maps

Shader Minifier can export symbol files that map the minified code back to names from the original source code. This lets you visualize shader size using https://github.com/ConspiracyHu/rekkrunchy-with-analytics

Shader Minifier performance

On my machine, it takes around 1s to minify a shader. A lot of that time comes from the startup time of the binary. If you have many shaders, try to minify them all at the same time by listing them all on the command-line.

Transformations

• Whitespace and comments removal
• Parentheses simplifications
• Curly braces removal
• Literal numbers
• Constant arithmetic
• Conditionals evaluation
• Commutative operators
• Comma operator
• Useless else after return
• Ternary operator
• Loops
• Merge declarations
• Group declarations
• Augmented operators
• Rename vector fields
• Automatic inlining
• Aggressive inlining
• Explicit inlining
• Reassignment merging
• Variable reuse
• Vector constructors
• Function predeclarations
• Unused local variables
• Dead code removal
• Unused function removal
• Other functions
• Renaming

Feedback

Please give feedback in the bugtracker. If something is blocking you, you can file a bug or update an existing bug. We rely on your feedback to prioritize the work.

Feature requests are encouraged. Add upvotes or comments to existing feature requests that are important to you.

Contributions are welcome. Please leave a message before implementing a significant change, so that we can agree on the solution.

Created by Laurent Le Brun (LLB / Ctrl-Alt-Test) and other contributors.

http://laurent.le-brun.eu — http://ctrl-alt-test.fr