Embed resources (eg, shader code; images) into executable/library with CMake

user_1072468 0
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I am writing an application in C++ which relies on various resources in my project. Right now, I have the relative path from the produced executable to each resource hard-coded in my sources, and that allows my program to open the files and read in the data in each resource. This works ok, but it requires that I start the executable from a specific path relative to the resources. So if I try to start my executable from anywhere else, it fails to open the files and cannot proceed.

Is there a portable way to have CMake embed my resources into the executables (or libraries) such that I can simply access them in memory at runtime instead of opening files whose paths are brittle? I have found a related question, and it looks like embedding resources can be done well enough with some ld magic. So my question is how do I do this in a portable, cross platform manner using CMake? I actually need my application run on both x86 and ARM. I am ok with supporting only Linux (Embedded), but bonus points if anyone can suggest how to do this for Windows (Embedded) as well.

EDIT: I forgot to mention a desired property of the solution. I would like to be able to use CMake to cross-compile the application when I am building for ARM rather than have to compile it natively on my ARM target.

embedded-resource cross-compiling cmake c++
6 Answers

I would like to propose another alternative. It uses the GCC linker to directly embed a binary file into the executable, with no intermediary source file. Which in my opinion is simpler and more efficient.

set( RC_DEPENDS "" )

function( add_resource input )
    string( MAKE_C_IDENTIFIER ${input} input_identifier )
    set( output "${CMAKE_ARCHIVE_OUTPUT_DIRECTORY}/${input_identifier}.o" )
    target_link_libraries( ${PROJECT_NAME} ${output} )

    add_custom_command(
        OUTPUT ${output}
        COMMAND ${CMAKE_LINKER} --relocatable --format binary --output ${output} ${input}
        DEPENDS ${input}
    )

    set( RC_DEPENDS ${RC_DEPENDS} ${output} PARENT_SCOPE )
endfunction()

# Resource file list
add_resource( "src/html/index.html" )

add_custom_target( rc ALL DEPENDS ${RC_DEPENDS} )

Then in your C/C++ files all you need is:

extern char index_html_start[] asm( "_binary_src_html_index_html_start" );
extern char index_html_end[]   asm( "_binary_src_html_index_html_end" );
extern size_t index_html_size  asm( "_binary_src_html_index_html_size" );
user_8942090

Pure CMake function to convert any file into C/C++ source code, implemented with only CMake commands:

####################################################################################################
# This function converts any file into C/C++ source code.
# Example:
# - input file: data.dat
# - output file: data.h
# - variable name declared in output file: DATA
# - data length: sizeof(DATA)
# embed_resource("data.dat" "data.h" "DATA")
####################################################################################################

function(embed_resource resource_file_name source_file_name variable_name)

    file(READ ${resource_file_name} hex_content HEX)

    string(REPEAT "[0-9a-f]" 32 column_pattern)
    string(REGEX REPLACE "(${column_pattern})" "\\1\n" content "${hex_content}")

    string(REGEX REPLACE "([0-9a-f][0-9a-f])" "0x\\1, " content "${content}")

    string(REGEX REPLACE ", $" "" content "${content}")

    set(array_definition "static const unsigned char ${variable_name}[] =\n{\n${content}\n};")

    set(source "// Auto generated file.\n${array_definition}\n")

    file(WRITE "${source_file_name}" "${source}")

endfunction()

https://gist.github.com/amir-saniyan/de99cee82fa9d8d615bb69f3f53b6004

user_3097980

There is a single-file CMake script that allows you to embed data easily that's called cmrc.

Example usage:

include(CMakeRC.cmake)
cmrc_add_resource_library(foo-resources
        ALIAS foo::rc
        NAMESPACE foo
        shaders/trig.vert
        shaders/trig.frag)

target_link_libraries(foo foo::rc)

#include <cmrc/cmrc.hpp>

CMRC_DECLARE(foo); // It should be the NAMESPACE property you specified
                   // in your CMakeLists.txt

int main() {
    auto fs = cmrc::foo::get_filesystem();
    auto vert_shader = fs.open("shaders/trig.vert");
    auto frag_shader = fs.open("shaders/trig.frag");
    ...
    glShaderSource(vertexShader, 1, &vert_shader.begin(), nullptr);
}

It's probably the easiest library to setup and use.

user_99725890
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