Loading and Using Fragment Shader

OpenGL OpenGL: Basic Coding
1

Hello, hope this is the place for the question.

Basically im trying to load a fragment shader into openGL and apply it to a mesh…

Shader Code:


void main()
	{
	gl_FragColor = vec4(0.4,0.4,0.8,1.0);
	}

Loading Shader: (I’ve put a cout<<glGetError<<endl; after each line and they all seem to succeed)


const char *shaderArray = &file_string;
shader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource( shader, 1, &shaderArray, NULL );
glCompileShader( shader );
program = glCreateProgram();
glAttachShader( program, shader );
glLinkProgram( program );

Then after the glUseProgram a GL_INVALID_OPERATION is generated…


if( glIsProgram( program ) )
{
glUseProgram( program );
cout<<"Error Code: "<<glGetError()<<endl;
}

I’m assuming its due to:
“GL_INVALID_OPERATION is generated if program could not be made part of current state.”
OpenGL Reference Manual

But I can’t see why this is - the use Program is called once GL is initiated and everything…

I’m sure its some silly mistake, but any help would be greatly appreciated.

Thanks in Advance

  • Jorj
2

you should check if shader got compiled and linked correct. the first for sure. query the compile and link strings for errors or warning. i forgot the exact code though. google.

3

If you do not know this tutorial already, I suggest you to check out the Lighthouse3D GLSL tutorial. It is a good tutorial to start with glsl and you will find how to handle errors.

4

Awesome, there was an error, it was in loading the string into openGL, and converting char array to “const char **”'s…

Thanks for your help

  • Jorj