Why is GLKView's DrawableWidth not set in ViewDidLoad?

Question

I'm using GLKit's GLKViewController/GLKView to do some basic OpenGL drawing.

I'd like to setup the ViewPort in the ViewDidLoad method. After reading the GLKView reference, I thought I'd be able to do it like this:

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
    if (!self.context) {
        NSLog(@"Failed to create ES context");
    }
    GLKView *view = (GLKView *)self.view;
    view.context = self.context;
    glViewport( 0, 0, view.DrawableWidth, view.DrawableHeight );
}

The problem is that both DrawableWidth and DrawableHeight properties are zero. Why is that? When the GLKView calls DrawInRect, they're set and their values are what I would expect.

score 3 · Accepted Answer · answered Mar 04 '12 at 18:53

3

The GLKView Class Reference says this:

After this, the view automatically creates or updates the framebuffer object whenever the view must be redrawn.

The framebuffer hasn't been created by the time you receive viewDidLoad, because the view hasn't needed to be drawn yet. So the dimensions of the framebuffer don't exist either.

It would be inappropriate for the system to create the framebuffer by this time. The view hasn't been added to the on-screen view hierarchy yet. After it's added to the on-screen view hierarchy, its size might be adjusted, which would require throwing away the old framebuffer and creating a new one.

The view waits until it is actually asked to draw itself to create the framebuffer so it doesn't waste time creating a framebuffer just to throw away later.

answered Mar 04 '12 at 18:53

rob mayoff

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Thanks for the clarification, I guess I should just use `view.frame.size` to set it up. – Gabriel G. Roy Mar 04 '12 at 19:40
`viewDidLoad` is not a great time to use `view.frame.size` either. http://stackoverflow.com/a/9540935/77567 – rob mayoff Mar 04 '12 at 19:44
So...when is a good time, @rob? EDIT: Oh, probably it's just better to use `UIScreen.mainScreen().bounds.width` and `height`. – Grumdrig Jan 09 '16 at 08:00
1

`viewDidLayoutSubviews`. – rob mayoff Jan 09 '16 at 08:03
For the record, they don't seem to be set then either, so I'm using `UIScreen.mainScreen().bounds` there too. (Pardon my Swift in an ObjC question.) – Grumdrig Jan 09 '16 at 08:13

score 1 · Answer 2 · edited Sep 27 '15 at 11:04

1

You must call first [view bindDrawable];

Then drawableWidth and height will be correct. It is because after setup frame buffer is un-binded and drawableWidth / height reflects framebuffer properties.

edited Sep 27 '15 at 11:04

Koopakiller

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answered Sep 27 '15 at 10:11

user5381284

11
1

Why is GLKView's DrawableWidth not set in ViewDidLoad?

2 Answers2