Shaders and Shader Program

We need to program at least a Vertex and Fragment shader to tell OpenGL what to do with the incomming Vertex and Pixel data.

Vertex Shader

A vertex shader is handling vertices. Lets create one with glCreateShader.

GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);

Now we have to tell where to find the source of it. We do that with glShaderSource.

const GLchar* vertexShaderSource = {
    "#version 450\n"
    "layout(location = 0) in vec3 iposition;\n"
    "layout(location = 1) in vec3 icolor;\n"
    "out vec4 color;"
    "void main() {\n"
    "color = vec4(icolor, 1.0f);\n"
    "gl_Position = vec4(iposition, 1.0f);\n"
    "}"
};

glShaderSource(vertexShader, 1, &vertexShaderSource, nullptr);

After telling how the source looks like we have to compile the source with glCompileShader.

glCompileShader(vertexShader);

Fragment Shader

A fragment shader is handling pixels (multiple pixels = fragments). We create it with the same function as we used for the vertex shader but with a different parameter.

GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);

Then of course we have to tell again where to find the source as we did for the vertex shader.

const GLchar* fragmentShaderSource = {
    "#version 450\n"
    "in vec4 color;\n"
    "layout(location = 0) out vec4 ocolor;\n"
    "void main() {\n"
    "  ocolor = color;\n"
    "}"
};

glShaderSource(fragmentShader, 1, &fragmentShaderSource, nullptr);

And of course the same, we have to compile this fragment shader too.

glCompileShader(fragmentShader);

Shader Program

The shader program holds different shader types and will be used during rendering. We create a shader program with glCreateProgram.

GLuint shaderProgram = glCreateProgram();

Now we need to attach the shaders we created before to this shader program. We do that with glAttachShader.

glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);

And finally as we do for normal c/c++ programs we have to link them to the shader program. This is done with glLinkProgram.

glLinkProgram(shaderProgram);

At this point if we don't have any errors, we are ready to use this shader program.