opengl Shader Loading and Compilation Load Separable Shader in C++


Example

4.1

This code loads, compiles, and links a single file that creates a separate shader program for a single stage. If there are errors, it will get the info-log for those errors.

The code uses some commonly-available C++11 functionality.

#include <string>
#include <fstream>

//In C++17, we could take a `std::filesystem::path` instead of a std::string
//for the filename.
GLuint CreateSeparateProgram(GLenum stage, const std::string &filename)
{
    std::ifstream input(filename.c_str(), std::ios::in | std::ios::binary | std::ios::ate);
    
    //Figure out how big the file is.
    auto fileSize = input.tellg();
    input.seekg(0, ios::beg);
    
    //Read the whole file.
    std::string fileData(fileSize);
    input.read(&fileData[0], fileSize);
    input.close();
    
    //Compile&link the file
    auto fileCstr = (const GLchar *)fileData.c_str();
    auto program = glCreateShaderProgramv(stage, 1, &fileCstr);

    //Check for errors
    GLint isLinked = 0;
    glGetProgramiv(program, GL_LINK_STATUS, &isLinked);
    if(isLinked == GL_FALSE)
    {
        //Note: maxLength includes the NUL terminator.
        GLint maxLength = 0;
        glGetProgramiv(program, GL_INFO_LOG_LENGTH, &maxLength);        

        //C++11 does not permit you to overwrite the NUL terminator,
        //even if you are overwriting it with the NUL terminator.
        //C++17 does, so you could subtract 1 from the length and skip the `pop_back`.
        std::basic_string<GLchar> infoLog(maxLength);
        glGetProgramInfoLog(program, maxLength, &maxLength, &infoLog[0]);
        infoLog.pop_back();

        //The program is useless now. So delete it.
        glDeleteProgram(program);

        //Use the infoLog in whatever manner you deem best.

        //Exit with failure.
        return 0;
    }
    
    return program;
}