如何使用IOS的openGL ES绘制一个简单的矩形？

Question

I am extremely new to openGL ES and the tutorials that I found online don't really make any sense to me. I am trying to just draw a simple 2D rectangle on the screen in IOS Objective C but I can't figure out how to do it. I found this on some tutorial but it doesn't do anything:

- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect {
GLfloat square[] = {
    0.25, 0.25, 0.0,
    0.75, 0.25, 0.0,
    0.25, 0.75, 0.0,
    0.75, 0.75, 0.0
};
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glVertexPointer(3, GL_FLOAT, 0, square);
glEnableClientState(GL_VERTEX_ARRAY);
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 4);
glFlush();


glOrthof(0.0f, 1.0f, 0.0f, 1.0f, -1.0f, 1.0f);


glClear(GL_COLOR_BUFFER_BIT);}

anything that will effectively draw a square/rectangle with some explanation will be very much appreciated. Thanks!

Answer 1

The code you posted might work in OpenGL ES 1.0.

However, GLKit, which you appear to be using, uses OpenGL ES 2.0. None of the function calls you're making have any effect in an OpenGL ES 2.0 context.

In GLES 1.0, as your code demonstrates, you draw things in "immediate mode." Equivalent code in OpenGL ES 2.0 has to create an appropriate shader program, and then provide vertex data to the GPU as a VBO (and potentially also create a VAO for good performance

I think explaining even something as simple as how to draw a triangle is beyond the scope of a StackOverflow answer, given the complexity of OpenGL. However, you can study the XCode Game Template (make a new Xcode project, chose the game template, and OpenGL ES as your technology), and googling for "OpenGL ES 2.0 tutorial" will probably provide a wealth of information.