Question

I am trying to experiment using basic shaders in my program, I came across a nice tutorial that talks you through writing a basic shader “util class” i guess you would call it? Which should allow me to apply a vertex and fragment shader…So I linked glew to my project (i have also glu, glut and glaux included) and inserted the following into a header file

#include "include\gl\glew.h"
#include <math.h>
#include <stdio.h>
#include <stdlib.h>

static struct {
    /* ... fields for buffer and texture objects */
    GLuint vertex_shader, fragment_shader, program;

    struct {
        GLint fade_factor;
        GLint textures[2];
    } uniforms;

    struct {
        GLint position;
    } attributes;

    GLfloat fade_factor;
} g_resources;

static GLuint make_shader(GLenum type, const char *filename)
{
    GLint length;
    char *source = file_content(filename, &length);
    GLuint shader;
    GLint shader_ok;

    if (!source)
        return 0;
    shader = glCreateShader(type);
    glShaderSource(shader, 1, (const GLchar**)&source, &length);
    free(source);
    glCompileShader(shader);
    glGetShaderiv(shader, GL_COMPILE_STATUS, &shader_ok);
    if (!shader_ok) {
        fprintf(stderr, "Failed to compile %s:\n", filename);
        show_info_log(shader, glGetShaderiv, glGetShaderInfoLog);
        glDeleteShader(shader);
        return 0;
    }
    return shader;
}

static void show_info_log(
    GLuint object,
    PFNGLGETSHADERIVPROC glGet__iv,
    PFNGLGETSHADERINFOLOGPROC glGet__InfoLog)
{
    GLint log_length;
    char *log;

    glGet__iv(object, GL_INFO_LOG_LENGTH, &log_length);
    log = malloc(log_length);
    glGet__InfoLog(object, log_length, NULL, log);
    fprintf(stderr, "%s", log);
    free(log);
}

static GLuint make_program(GLuint vertex_shader, GLuint fragment_shader)
{
    GLint program_ok;

    GLuint program = glCreateProgram();
    glAttachShader(program, vertex_shader);
    glAttachShader(program, fragment_shader);
    glLinkProgram(program);
     glGetProgramiv(program, GL_LINK_STATUS, &program_ok);
    if (!program_ok) {
        fprintf(stderr, "Failed to link shader program:\n");
        show_info_log(program, glGetProgramiv, glGetProgramInfoLog);
        glDeleteProgram(program);
        return 0;
    }
    return program;
}

static int make_resources(void)
{
    /* make buffers and textures ... */
    g_resources.vertex_shader = make_shader(
        GL_VERTEX_SHADER,
        "hello-gl.v.glsl"
    );
    if (g_resources.vertex_shader == 0)
        return 0;

    g_resources.fragment_shader = make_shader(
        GL_FRAGMENT_SHADER,
        "hello-gl.f.glsl"
    );
    if (g_resources.fragment_shader == 0)
        return 0;

    g_resources.program = make_program(
        g_resources.vertex_shader,
        g_resources.fragment_shader
    );
    if (g_resources.program == 0)
        return 0;
    g_resources.uniforms.fade_factor
        = glGetUniformLocation(g_resources.program, "fade_factor");
    g_resources.uniforms.textures[0]
        = glGetUniformLocation(g_resources.program, "textures[0]");
    g_resources.uniforms.textures[1]
        = glGetUniformLocation(g_resources.program, "textures[1]");

    g_resources.attributes.position
        = glGetAttribLocation(g_resources.program, "position");

    return 1;
}

But my compiler complains about the following:

9   IntelliSense: "GLchar" is not a type name   

    11  IntelliSense: a value of type "void *" cannot be assigned to an entity of type "char *" 

    7   IntelliSense: identifier "file_contents" is undefined   

    5   IntelliSense: identifier "GLchar" is undefined

Am I missing something? I searched the internet and it seems like GLchar and the file_contents function do exist?

Answer 1

The error line you gave is the compiler telling you, that it doesn’t know about the type GLchar, which is defined in GL/gl.h – or GL/glew.h in your case, which also defines it. But it seems to be not properly included.

Your first line should be

#include <GL/glew.h>

i.e. uppercae GL, a forward slash (backslashes are a Microsoaft addition, but forwards are accepted just fine), and the whole thing in angle brackets, as you want to include from the standard includes.

Next you should not link against glaux. That one is so outdated that it’s become toxic.

If you want a working OpenGL shader example program, I prepared one at https://github.com/datenwolf/codesamples/tree/master/samples/OpenGL/minimal_glsl