The following list summarizes iOS hardware available in devices of various generations. Current device shader performance can compared on gfxbench which compares different hardware features using benchmarks.
The iPhone 4S, with the A5 chip, is capable of rendering complex shaders throughout the entire screen. Even image effects may be possible. However, optimizing your shaders is still crucial. But if your game isn’t trying to push limits of the device, optimizing scripting and gameplay is probably as much of a waste of time on this generation of devices as it is on PC.
iPad2: the A5 can do full screen bumpmapping, assuming the shader is simple enough. However, it is likely that your game will perform best with bumpmapping only on crucial objects. Full screen image effects still out of reach. Scripting optimization less important.
The iPad 3 has been shown to be capable of render-to-texture effects such as reflective water and fullscreen image effects. However, optimized shaders are still crucial. But if your game isn’t trying to push limits of the device, optimizing scripting and gameplay is probably as much of a waste of time on this generation of devices as it is on PC.
The iPhone/iPad graphics processing unit (GPU) is a Tile-Based Deferred Renderer. In contrast with most GPUs in desktop computers, the iPhone/iPad GPU focuses on minimizing the work required to render an image as early as possible in the processing of a scene. That way, only the visible pixels will consume processing resources.
The GPU’s frame buffer is divided up into tiles and rendering happens tile by tile. First, triangles for the whole frame are gathered and assigned to the tiles. Then, visible fragments of each triangle are chosen. Finally, the selected triangle fragments are passed to the rasterizer (triangle fragments occluded from the camera are rejected at this stage).
In other words, the iPhone/iPad GPU implements a Hidden Surface Removal operation at reduced cost. Such an architecture consumes less memory bandwidth, has lower power consumption and utilizes the texture cache better. Tile-Based Deferred Rendering allows the device to reject occluded fragments before actual rasterization, which helps to keep overdraw low.
For more information, see also:
iOS devices support these texture compression formats:
PVRTC provides support for RGB and RGBA (color information plus an alpha channel) texture formats and can compress a single pixel to two or four bits. The PVRTC format is essential to reduce the memory footprint and to reduce consumption of memory bandwidth, as in the rate at which data can be read from memory, which is usually very limited on mobile devices.
ETC compresses 4x4 pixel blocks into 64-bit quantities, but lacks an alpha channel.
ETC2 supports both 1-bit and 8-bit alpha channel compression.
ASTC is flexible format that uses pixel block sizes. It’s supported by Metal and OpenGL ES 3.0 graphic APIs.
Note: the DXT texture compression format on iOS devices is NOT supported.
For detailed texture compression options in iOS, see iOS 2D Texture Overrides.
The iPhone/iPad has a dedicated unit responsible for vertex processing which runs calculations in parallel with rasterization. In order to achieve better parallelization, the iPhone/iPad processes vertices one frame ahead of the rasterizer.
Both the CPU and GPU on the iPhone/iPad share the same memory. The advantage is that you don’t need to worry about running out of video memory for your textures (unless, of course, you run out of main memory too). The disadvantage is that you share the same memory bandwidth for gameplay and graphics. The more memory bandwidth you dedicate to graphics, the less you will have for gameplay and physics.
The iPhone/iPad main CPU is equipped with a powerful SIMD (Single Instruction, Multiple Data) coprocessor supporting either the VFP or the NEON architecture. The Unity iOS run-time takes advantage of these units for multiple tasks such as calculating skinned mesh transformations, geometry batching, audio processing and other calculation-intensive operations.