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c++openglsdlsdl-2

Switching from OpenGL 2.1 with GLSL 1.2 to OpenGL 3.3 with GLSL version 1.5 breaks my code

I am trying to switch my OpenGL version from OpenGL 2.1 to OpenGL 3.3. The minimal reproducible OpenGL 3.3 code is as follows:

#include <stdio.h>

#include <SDL2/SDL.h>
#include <GL/glew.h>

static const GLuint WIDTH = 512;
static const GLuint HEIGHT = 512;
static const GLchar* vertex_shader_source =
"#version 330\n"
"in vec2 coord2d;\n"
"void main() {\n"
"    gl_Position = vec4(coord2d, 0.0, 1.0);\n"
"}\n";
static const GLchar* fragment_shader_source =
"#version 330\n"
"out vec4 color;\n"
"void main() {\n"
"    color = vec4(1.0, 0.0, 0.0, 1.0);\n"
"}\n";
static GLfloat vertices[] = {
    0.0,  0.8,
    -0.8, -0.8,
    0.8, -0.8,
};

GLuint common_get_shader_program(
                                 const char *vertex_shader_source,
                                 const char *fragment_shader_source
                                 ) {
    GLchar *log = NULL;
    GLint log_length, success;
    GLuint fragment_shader, program, vertex_shader;

    /* Vertex shader */
    vertex_shader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertex_shader, 1, &vertex_shader_source, NULL);
    glCompileShader(vertex_shader);
    glGetShaderiv(vertex_shader, GL_COMPILE_STATUS, &success);
    glGetShaderiv(vertex_shader, GL_INFO_LOG_LENGTH, &log_length);
    log = (char*) malloc(log_length);
    if (log_length > 0) {
        glGetShaderInfoLog(vertex_shader, log_length, NULL, log);
        printf("vertex shader log:\n\n%s\n", log);
    }
    if (!success) {
        printf("vertex shader compile error\n");
        exit(EXIT_FAILURE);
    }

    /* Fragment shader */
    fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragment_shader, 1, &fragment_shader_source, NULL);
    glCompileShader(fragment_shader);
    glGetShaderiv(fragment_shader, GL_COMPILE_STATUS, &success);
    glGetShaderiv(fragment_shader, GL_INFO_LOG_LENGTH, &log_length);
    if (log_length > 0) {
        log = (char*)realloc(log, log_length);
        glGetShaderInfoLog(fragment_shader, log_length, NULL, log);
        printf("fragment shader log:\n\n%s\n", log);
    }
    if (!success) {
        printf("fragment shader compile error\n");
        exit(EXIT_FAILURE);
    }

    /* Link shaders */
    program = glCreateProgram();
    glAttachShader(program, vertex_shader);
    glAttachShader(program, fragment_shader);
    glLinkProgram(program);
    glGetProgramiv(program, GL_LINK_STATUS, &success);
    glGetProgramiv(program, GL_INFO_LOG_LENGTH, &log_length);
    if (log_length > 0) {
        log = (char*)realloc(log, log_length);
        glGetProgramInfoLog(program, log_length, NULL, log);
        printf("shader link log:\n\n%s\n", log);
    }
    if (!success) {
        printf("shader link error");
        exit(EXIT_FAILURE);
    }

    /* Cleanup. */
    free(log);
    glDeleteShader(vertex_shader);
    glDeleteShader(fragment_shader);
    return program;
}

int main(void) {
    GLint attribute_coord2d;
    GLuint program, vbo;
    SDL_Event event;

    SDL_Init(SDL_INIT_TIMER | SDL_INIT_VIDEO);
    SDL_GL_SetAttribute (SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute (SDL_GL_CONTEXT_MINOR_VERSION, 3);
    SDL_GL_SetAttribute (SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);

    SDL_Window *window;
    SDL_GLContext gl_context;
    window = SDL_CreateWindow(__FILE__, 0, 0,
                              WIDTH, HEIGHT, SDL_WINDOW_OPENGL);
    gl_context = SDL_GL_CreateContext(window);
    glewInit();

    /* Shader setup. */
    program = common_get_shader_program(vertex_shader_source, fragment_shader_source);
    attribute_coord2d = glGetAttribLocation(program, "coord2d");

    /* Buffer setup. */
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glVertexAttribPointer(attribute_coord2d, 2, GL_FLOAT, GL_FALSE, 0, 0);
    glBindBuffer(GL_ARRAY_BUFFER, 0);

    /* Global draw state */
    glUseProgram(program);
    glViewport(0, 0, WIDTH, HEIGHT);
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

    /* Main loop. */
    while (1) {
        glClear(GL_COLOR_BUFFER_BIT);
        glEnableVertexAttribArray(attribute_coord2d);
        glDrawArrays(GL_TRIANGLES, 0, 3);
        glDisableVertexAttribArray(attribute_coord2d);
        SDL_GL_SwapWindow(window);
        if (SDL_PollEvent(&event) && event.type == SDL_QUIT)
            break;
    }

    /* Cleanup. */
    glDeleteBuffers(1, &vbo);
    glDeleteProgram(program);
    SDL_GL_DeleteContext(gl_context);
    SDL_DestroyWindow(window);
    SDL_Quit();
    return EXIT_SUCCESS;
}

There are no compile time errors and no runtime errors, but it only renders a blank screen. However, when I change vertex_shader_source to 

"#version 120\n"
"attribute vec2 coord2d;\n"
"void main() {\n"
"    gl_Position = vec4(coord2d, 0.0, 1.0);\n"
"}\n";

fragment_shader_source to 

"#version 120\n"
"void main() {\n"
"    gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);\n"
"}\n";

and comment out the lines

SDL_GL_SetAttribute (SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute (SDL_GL_CONTEXT_MINOR_VERSION, 3);
SDL_GL_SetAttribute (SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);

the code works and I get the expected output.

enter image description here

It feels like the OpenGL 3.3 version of the code should work, especially considering there are very few differences between the two code snippets. I have also checked to make sure that the vertex buffer is being set correctly using glGetBufferSubData. As far as I can tell, it is being set correctly.

The only two possibilities I can think of are

  1. There is something I do not understand about the vertex shader and/or fragment shader source code.
  2. There is something wrong with my build process. I.e. a library is missing or not being linked.

Concerning the second possibility, I am using XCode on Mac OSX, and these are the libraries I am linking with.

enter image description here

Could anyone help me figure out what is wrong?

Solution

  • There are no compile time errors and no runtime errors, but it only renders a blank screen. However, when I change...

    In core mode you must have a named Vertex Array Object, because the default vertex array object "0" is not valid.

    So do you mean I need to add something like glGenVertexArrays(1, &vao); glBindVertexArray(vao); ? I just tried that, and I get "EXC_BAD_ACCESS (code=1, address=0x0)"

    glGenVertexArrays is available in since OpenGL version 3.0. If vertex array objects are supported can be checked by glewGetExtension("GL_ARB_vertex_array_object").

    Glew can enable additional extensions by:

    glewExperimental = GL_TRUE;
glewInit();

    See the GLEW documentation:

    GLEW obtains information on the supported extensions from the graphics driver. Experimental or pre-release drivers, however, might not report every available extension through the standard mechanism, in which case GLEW will report it unsupported. To circumvent this situation, the glewExperimental global switch can be turned on by setting it to GL_TRUE before calling glewInit(), which ensures that all extensions with valid entry points will be exposed.