Making Games in Open GL: Part 3 - Beginning OpenGL ES and GLKit - raywenderlich.com

This video continues you the overall tutorial on building a game in OpenGL. This is the third part of the series.

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About OpenGL

The Open Graphics Library (OpenGL) is used for visualizing 2D and 3D data. It is a multipurpose open-standard graphics library that supports applications for 2D and 3D digital content creation, mechanical and architectural design, virtual prototyping, flight simulation, video games, and more. You use OpenGL to configure a 3D graphics pipeline and submit data to it. Vertices are transformed and lit, assembled into primitives, and rasterized to create a 2D image. OpenGL is designed to translate function calls into graphics commands that can be sent to underlying graphics hardware. Because this underlying hardware is dedicated to processing graphics commands, OpenGL drawing is typically very fast.

OpenGL for Embedded Systems (OpenGL ES) is a simplified version of OpenGL that eliminates redundant functionality to provide a library that is both easier to learn and easier to implement in mobile graphics hardware.

OpenGL ES allows an app to harness the power of the underlying graphics processor. The GPU on iOS devices can perform sophisticated 2D and 3D drawing, as well as complex shading calculations on every pixel in the final image. You should use OpenGL ES if the design requirements of your app call for the most direct and comprehensive access possible to GPU hardware. Typical clients for OpenGL ES include video games and simulations that present 3D graphics.

OpenGL ES is a low-level, hardware-focused API. Though it provides the most powerful and flexible graphics processing tools, it also has a steep learning curve and a significant effect on the overall design of your app. For apps that require high-performance graphics for more specialized uses, iOS provides several higher-level frameworks:

The Sprite Kit framework provides a hardware-accelerated animation system optimized for creating 2D games. (See Sprite Kit Programming Guide.)

The Core Image framework provides real-time filtering and analysis for still and video images. (See Core Image Programming Guide.)

Core Animation provides the hardware-accelerated graphics rendering and animation infrastructure for all iOS apps, as well as a simple declarative programming model that makes it simple to implement sophisticated user interface animations. (See Core Animation Programming Guide.)

You can add animation, physics-based dynamics, and other special effects to Cocoa Touch user interfaces using features in the UIKit framework.

OpenGL ES Is a Platform-Neutral API Implemented in iOS

Because OpenGL ES is a C-based API, it is extremely portable and widely supported. As a C API, it integrates seamlessly with Objective-C Cocoa Touch apps. The OpenGL ES specification does not define a windowing layer; instead, the hosting operating system must provide functions to create an OpenGL ES rendering context, which accepts commands, and a framebuffer, where the results of any drawing commands are written to. Working with OpenGL ES on iOS requires using iOS classes to set up and present a drawing surface and using platform-neutral API to render its contents.

GLKit Provides a Drawing Surface and Animation Support

Views and view controllers, defined by the UIKit framework, control the presentation of visual content on iOS. The GLKit framework provides OpenGL ES–aware versions of these classes. When you develop an OpenGL ES app, you use a GLKView object to render your OpenGL ES content. You can also use a GLKViewController object to manage your view and support animating its contents.

iOS Supports Alternative Rendering Targets

Besides drawing content to fill an entire screen or part of a view hierarchy, you can also use OpenGL ES framebuffer objects for other rendering strategies. iOS implements standard OpenGL ES framebuffer objects, which you can use for rendering to an offscreen buffer or to a texture for use elsewhere in an OpenGL ES scene. In addition, OpenGL ES on iOS supports rendering to a Core Animation layer (the CAEAGLLayer class), which you can then combine with other layers to build your app’s user interface or other visual displays.