> On Jun 11, 2016, at 7:43 AM, Richard Charles <rcharles...@gmail.com> wrote:
>
> Before calling drawRect:, the system locks focus on the view. Each view has
> its own graphic context. When the focus is locked on a view, the view’s
> graphics context is active. When the focus is unlocked, the graphics context
> is no longer active. Drawing commands are always executed in the current
> graphic context.
> On Jun 16, 2016, at 6:19 PM, James Walker <jam...@frameforge3d.com> wrote:
>
> I doubt that it is necessary to lock focus on the view, because you are not
> really drawing in the view or even in the window. You are drawing in a
> separate "surface" that is normally in a layer above the window. See
> NSOpenGLCPSurfaceOrder.
A typical implementation of lockFocus for use with OpenGL might look like this.
- (void)lockFocus
{
NSOpenGLContext* context = [self openGLContext];
if ([context view] != self) {
[context setView:self];
}
[context makeCurrentContext];
}
If you have only one OpenGL context in your app and it is the current context
for the view then you do not need to lock focus. So I think the takeaway is
that draw calls operate within a graphic context. If the context you want and
need is the current context then you are good to go.
I suppose it might be different if you are drawing full screen rather than into
a window or view. Drawing full screen your app could still have multiple
graphic contexts. If your full screen app has only one graphic context then you
are good to go.
I am no expert in OpenGL or Cocoa but I think this is the way it works.
--Richard Charles
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