GLKit starter ViewController

ViewController.m

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController
{
    EAGLContext* context;
    GLuint vertexArray; // our VAO
    GLuint vertexBuffer; // our VBO for vertices
    GLuint indexBuffer; // our VBO for indices
    GLKBaseEffect* effect;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2]; // context creation
    // View setup
    GLKView* view = (GLKView*)self.view;
    view.context = context;
    view.drawableDepthFormat = GLKViewDrawableDepthFormat24;
    [EAGLContext setCurrentContext:context];
    
    GLKVector3 vertices[4];
    vertices[0] = GLKVector3Make(-0.5f, -0.5f, 0); // create a new GLKVector3 structure
    vertices[1] = GLKVector3Make(0.5f, -0.5f, 0);
    vertices[2] = GLKVector3Make(0.5f, 0.5f, 0);
    vertices[3] = GLKVector3Make(-0.5f, 0.5f, 0);
    
    GLuint indices[6];
    indices[0] = 0;
    indices[1] = 1;
    indices[2] = 2;
    indices[3] = 0;
    indices[4] = 2;
    indices[5] = 3;
    
    glGenVertexArraysOES(1, &vertexArray); // create the VAO
    glBindVertexArrayOES(vertexArray); // tell opengl we're using it
    
    // create the vertices VBO
    glGenBuffers(1, &vertexBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer); // tell opengl we're using it
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); // upload the date to the GPU
    
    // same story for the indices VBO
    glGenBuffers(1, &indexBuffer);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
    
    // tell opengl to activate position on shaders...
    glEnableVertexAttribArray(GLKVertexAttribPosition);
    // and use this part of our vertex data as input
    glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, sizeof(GLKVector3), 0);
    // close our VAO because we're done here
    glBindVertexArrayOES(0);
    
    effect = [[GLKBaseEffect alloc] init];
    // set up constant color
    effect.useConstantColor = GL_TRUE;
    effect.constantColor = GLKVector4Make(0, 1, 0, 1);
    // set up "camera"
    effect.transform.projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(60), fabsf(view.bounds.size.height / view.bounds.size.width), 0.1f, 100.f);
    effect.transform.modelviewMatrix = GLKMatrix4MakeTranslation(0, 0, -5);
}

-(void)viewDidUnload
{
    [super viewDidUnload];
    
    // delete our buffers GPU side
    glDeleteBuffers(1, &vertexBuffer);
    glDeleteBuffers(1, &indexBuffer);
    glDeleteVertexArraysOES(1, &vertexArray);
    // delete our context
    [EAGLContext setCurrentContext:context];
    if ([EAGLContext currentContext] == context)
        [EAGLContext setCurrentContext:nil];
    context = nil;
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

-(void)glkView:(GLKView *)view drawInRect:(CGRect)rect{
    glClearColor(1.0f, 0.0f, 1.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glBindVertexArrayOES(vertexArray); // use our VAO
    [effect prepareToDraw]; // do secret mysterious apple stuff
    glDrawElements(GL_TRIANGLES,  6, GL_UNSIGNED_INT, 0); // draw
    glBindVertexArrayOES(0); // don't use our VAO
}
@end