UInitWindow(argc, argv);

GlewInitResult = glewInit();

if (GLEW_OK != GlewInitResult) {
    fprintf(stderr, "ERROR: %sn", glewGetErrorString(GlewInitResult));
    exit(EXIT_FAILURE);
}

fprintf(stdout,"INFO: OpenGl Version: %sn", glGetString(GL_VERSION));

UCreateVBO(); //Calls the function to create the Vertex Buffer Object

UCreateShaders(); //Calls the function to create the Shader Program

glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

glutInit(&argc, argv);

glutInitWindowSize(WindowWidth, WindowHeight);

glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);

glutCreateWindow(WINDOW_TITLE);

glutReshapeFunc(UResizeWindow);
glutDisplayFunc(URenderGraphics);

/*Creates the Triangle*/
GLuint totalVerticies = 6; //Specifies the number of verticies for the triangel i.e.3
//glDrawArrays(GL_TRIANGLES, 0, totalVerticies); //Draws the Triangle

//Draw the triangles using the indicies
glDrawElements(GL_TRIANGLES, totalVerticies, GL_UNSIGNED_SHORT, NULL);

glutSwapBuffers();

//Specifies the coordinates for triangle verticles on x and y
GLfloat verts[]= {
        /*indices will be 0, 1, 2, 3, 4, 1
         * index 1 will be shared by both triangles
         */

        //index 0
        -1.f, 1.0f, //top-center of the screen
        1.0f, 0.0f, 0.0f, 1.0f, //Red Vertex

        //index 1
        -0.5f, 0.0f, //bottom-left of the screen
        0.0f , 1.0f, 0.0f, 1.0f, // Green Vertex

        //index 2
        -1.0f, 0.0f, //bottom-right of the screen
        0.0f, 0.0f, 1.0f, 1.0f, // Blue Vertex

        //index 3
        0.0, 0.0f, //topcenter of the screen
        1.0f, 0.0f, 0.0f, 1.0f, //Red Vertex

        //index 4
        0.0f, -1.0f, // bottom-left of the screen
        0.0f, 1.0f, 0.0f, 1.0f, // Green vertex

        //0.0, -1.0f, //bottom-right of the screen
        //0.0f, 0.0f, 1.0f, 1.0f //Blue Vertex
};

//stores the size of the verts array / number of coordinates needed for the triangle i.e 6
float numVerticles = sizeof(verts);

GLuint myBufferID; //Variable for vertex buffer object id
glGenBuffers(1, &myBufferID); //Creates 1 buffer
glBindBuffer(GL_ARRAY_BUFFER, myBufferID); //Activates the buffer
glBufferData(GL_ARRAY_BUFFER, numVerticles, verts, GL_STATIC_DRAW); //Sends vertex or coordinate data to the GPU

/* Creates the Vertex Attribute Pointer */
GLuint floatsPerVertex = 2; // Number of coordinates per vertex
glEnableVertexAttribArray(0); // Specifies the initial position of the coordinates in the buffer

/*Strides between vertex coordinates is 6 (x, y, r, g, b, a). A tightly packed stride is 0.*/
GLint vertexStride = sizeof(float) * 6; //The number of floats before each vertex position is 6 i.e. xyrgba

/* Instructs the GPI on how to handle the vertex buffer object data
 * parameters attribPointerPosition | coordinates per vertex | data type | deactivate normalization | 0 strides | 0 offset |
 */
glVertexAttribPointer(0, floatsPerVertex, GL_FLOAT, GL_FALSE, vertexStride, 0); //change the stride from 0 to 6

/* Sets an attribute pointer position for the vertex colors i.e Attribute 1 for rgba floats. Attribute 0 for postition x,y */
glEnableVertexAttribArray(1); //Specifies position 1 for the color values in the buffer

GLint colorStride = sizeof(float) * 6; //The number of floats before each color is 6 i.e. rgba xy

//Parameters: attribPointerPosition 1 | floats per color is 4 i.e. rgba | data type | deactivate normalization | 6 strides until next color i.e. rgbazy | 2 floats until the beginning of each color i.e xy
glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, colorStride, (char*)(sizeof(float)*2));

/*Creates a buffer for the indices*/
GLushort indicies[] = {0,1,2, 3,4,1}; //Using index 1 twice
float numIndicies = sizeof(indicies);
GLuint indexBufferID;
glGenBuffers(1, &indexBufferID);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBufferID);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, numIndicies, indicies, GL_STATIC_DRAW);

GLuint vertexShaderId = glCreateShader(GL_VERTEX_SHADER); //Create a Vertex Shader object
GLuint fragmentShaderId = glCreateShader(GL_FRAGMENT_SHADER); //Create a Vertex Shader object

glShaderSource(vertexShaderId, 1, &VertexShader, NULL); //retrieves the vertex shader source code
glShaderSource(fragmentShaderId, 1, &FragmentShader, NULL); //retrieves the fragment shader source code

glCompileShader(vertexShaderId); //compile the vertex shader
glCompileShader(fragmentShaderId); //compile the fragment shader

//Attaches the vertex and fragment shader to the shader program
glAttachShader(ProgramId, vertexShaderId);
glAttachShader(ProgramId, fragmentShaderId);

glLinkProgram(ProgramId); //Links the shader program
glUseProgram(ProgramId); //Uses Shader Program