I am running the boiler plate OpenGL example code that XCode creates for an OpenGL project for iOS. This sets up a simple ViewController and uses GLKit to handle the rest of the work.
All the update/draw functionality of the application is in C++. It is cross platform.
There is a lot of framebuffer creation going on. The draw phase renders to a few frame buffers and then tries to set it back to the default framebuffer.
glBindFramebuffer(GL_FRAMEBUFFER, 0);
This generates an GL_INVALID_ENUM. Only on iOS.
I am completely stumped as to why. The code runs fine on all major platforms except iOS. I’m wanting to blame GLKit. Any examples of iOS OpenGL setup that do not use GLKit?
UPDATE
The following snippet of code lets me see the default framebuffer that GLKit is using. For some reason it comes out as “2”. Sure enough if I use “2” in all my glBindFrameBuffer calls it works. This is very frustrating.
[view bindDrawable ];
GLint defaultFBO;
glGetIntegerv(GL_FRAMEBUFFER_BINDING_OES, &defaultFBO);
LOGI("DEFAULT FBO: %d", defaultFBO);
What reason on earth would cause GLKit to not generate its internal framebuffer at 0? This is the semantic all other implementations of OpenGL use, 0 is the default FBO.
On iOS there is no default framebuffer. See Framebuffer Objects are the Only Rendering Target on iOS. I don’t know much about GLKit, but on iOS to render something on screen you need to create framebuffer, and attach to it renderbuffer, and inform Core Animation Layer that this renderbuffer will be the “screen” or “default framebuffer” to draw to. Meaning – everything you’ll draw to this framebuffer, will appear on screen. See Rendering to a Core Animation Layer.