Question

VC++ 2010, SDL, OpenGL, GLSL

I am working on this class as a way to switch between shaders quick and easily. It seems to be working properly(functionality-wise), however the framerate drops severely after implementing it(from 60 to 40). Hopefully you guys can point me in the right direction.

Here is what I have so far:

namespace SL {

struct Shader_Manager {

    struct shader_vect {

        GLuint      shader_type;
        GLuint      shader_handle;
        char *      filename;
    };

    struct search_vect
    {
        std::string target;
        bool operator()(const shader_vect& vect) const
        {
            return vect.filename == target;
        }
    };

    GLuint          prog;
    std::vector     <shader_vect> shader_list;

    GLuint          vertex_shader;
    GLuint          fragment_shader;

    Shader_Manager() {

        prog = glCreateProgram();
    };

    ~Shader_Manager() {};

    void load(char * filename, int type) {

        shader_vect shader;

        shader.filename             = filename;
        shader.shader_type          = type;

        shader.shader_handle        = glCreateShader(type);
        char * fs                   = textFileRead(filename);

        const char * vv = fs;
        glShaderSource(shader.shader_handle, 1, &vv, NULL);

        free(fs);
        glCompileShader(shader.shader_handle);

        shader_list.push_back(shader);
    }

    void use(char * filename) {

        search_vect search;
        search.target = filename;

        std::vector<shader_vect>::iterator it = 
                std::find_if(shader_list.begin(), shader_list.end(), search);

        glAttachShader(prog, it->shader_handle);

        glLinkProgram(prog);
        glUseProgram(prog);
    }

    void end() {

        glLinkProgram(0);
        glUseProgram(0);
    }
};
} // namespace SL

inside my main function I use it like such:

SL::Shader_Manager SLManager;
SLManager.load("shader.frag", GL_FRAGMENT_SHADER);

and withing the game loop I am doing:

SLManager.use("shader.frag");
  makeSphere();
SLManager.end();

Am I not properly free’ing up some resources? Any help would be appreciated, thanks!

Answer 1

Linking a program every time you switch is a mistake. You should create as many programs as you need, all shader objects and then link everything that you will need. Then just call glUseProgram on a switch (possibly have a debug mode that calls glGet(GL_CURRENT_PROGRAM) and alerts for unnecessary switches, because those are, essentially, bugs.