Question

I am attempting to build a simple OpenGL 3.2 program which consists of a single fragment shader, but I do not seem to be able to actually compile the shader. I’m fairly sure that my shader syntax is correct, but even if it’s not, I am unable to retrieve an error message using glGetShaderInfoLog.

I have developed a short program that shows this in action:

GLuint shader = glCreateShader(GL_FRAGMENT_SHADER);

const char *shaderData =
            "#version 120\n"
            "void main()\n"
            "{\n"
            "    gl_FragColor = gl_Color;\n"
            "}\n";
glShaderSource(shader, 1, &shaderData, NULL);

GLint status;
glGetShaderiv(shader, GL_COMPILE_STATUS, &status);

if (status == GL_FALSE)
{
    GLint infoLogLength;
    glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &infoLogLength);

    GLchar* strInfoLog = new GLchar[infoLogLength + 1];
    glGetShaderInfoLog(shader, infoLogLength, NULL, strInfoLog);

    fprintf(stderr, "Compilation error in shader %s: %s\n", this->name, strInfoLog);
    delete[] strInfoLog;
}

This yields the message:

Compilation error in shader Fragment Shader:

The issue seems to be that the call to getShaderiv to retrieve the GL_INFO_LOG_LENGTH value returns 0 every time, so therefore I allocate an empty string. I have tried hard-coding this value to 100, but I still receive nothing from getShaderInfoLog.

My concern here is not to fix the shader (I can do that myself if it is wrong), but to get the debug information. I know that this can be done, because I have used Shader Maker to develop shaders briefly, and I am able to get very detailed debug messages. For example:

ERROR: 0:11: 'undefined_variable' : syntax error syntax error

Unless Shader Marker has its own validation tool internally, I’m sure it has to be using the same method that I am trying to use. I have seen several examples on the internet in which people retrieve the error message for a shader in the same way, so I’m fairly sure I’m doing it correctly.

Now, I am getting a compile-time warning which could potentially explain this problem:

#warning gl.h and gl3.h are both included. Compiler will not invoke errors if using removed OpenGL functionality.

After doing a full text search, I cannot find anywhere where I call #include <OpenGL/gl.h>, so I am guessing that this header is being included by one of the NSOpenGL* classes. I’m fairly sure that I’m not using any removed functionality in this short program, and this issue only has about 5 hits on Google, but I thought I’d better mention this anyway.

Answer 1

As noted in a previous comment, the glCompileShader call was missing.