This is a great article on why and how to take advantage of the hardware scaler available on Android platforms. This advice also applies to PC game developers where rendering to smaller buffers is common practice for performance reasons.
Developers may also consider a hybrid approach where they render the 3d elements of their scene to a reduced resolution back buffer, scale this to the intended display resolution and then render 2D user interface elements such as text at the final display resolution. This has the advantage of ensuring that the user interface is rendered as sharply as possible.
If fill rate is a big concern another solution is to perform a Z pre-pass. All of the scenes geometry is rendered using an inexpensive pixel shader. This primes the Z buffer for the actual render pass ensuring that the expensive final pixel shaders are only run for visible pixels.
Another easy tip is to try to render from front to back. This occludes as much of the render buffer as early as possible again reducing the total amount of pixel shading required.
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