RenderScript in the Android Support Library

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The RenderScript Support Library lets you take advantage of the latest RenderScript features on devices running Android 2.2 and later.

Posted by Tim Murray, Android RenderScript team

One of the requests we hear most commonly from developers is to enable more devices to run the latest features of RenderScript. Over the past several releases of Android, we’ve added a ton of functionality to the RenderScript runtime, but the runtime's dependence on the core Android platform version has limited the range of devices that can support that new functionality. We’ve been working on a solution to this since last year, and we’re now ready to share it with all Android developers.

Today we're announcing a new RenderScript Support Library and updated SDK tools that together let you take advantage of RenderScript on plaform versions all the way back to Android 2.2 (Froyo).

With ADT v22.2, SDK Tools v22.2, and Android Build Tools v18.1.0, apps targeting Android 2.2 and later can now make use of almost all of the functionality available natively in RenderScript with Android 4.3. This includes access to the newest RenderScript features such as high-performance intrinsics and the new performance optimizations available to scripts.

Using the RenderScript Support Library

Using the RenderScript Support Library is straightforward. Once you've updated ADT and your SDK tools, there are only two things that you have to do to start using Renderscript in your apps:

1. In your classes that use RenderScript, import the RenderScript Support Library from android.support.v8.renderscript. If you are already using native RenderScript, you can change your import from android.renderscript to android.support.v8.renderscript.
   
   

   import android.support.v8.renderscript.*;

   
   


2. In your project.properties, make sure you’re targeting android-18 and add the following lines:
   
   

   renderscript.target=18
   renderscript.support.mode=true
   sdk.buildtools=18.1.0

That’s it! With the RenderScript Support Library, you can continue to use the same APIs from your app as with the native RenderScript package (with a few minor exceptions that we’ll talk about below), and you can use the same features in your own scripts as you would with the latest RenderScript toolchain.

For complete details on how to set up the RenderScript Support Library, see Accessing RenderScript Java APIs.

API and Implementation details

If you'd like to use RenderScript Support Library in your app, there are few things you should know:

• First, the RenderScript Support Library supports almost all of the RenderScript API functions as the native API that's available in API level and higher. The one notable exception is that Allocation.USAGE_IO_INPUT and Allocation.USAGE_IO_OUTPUT are not currently available in the RenderScript Support Library.



• Second, devices running Android 4.2 and earlier will always run their RenderScript applications on the CPU, while devices running Android 4.3 or later will run their RenderScript applications on whatever processors are available on that particular device. Because the Support Library versions of the scripts have to be precompiled to support all possible platforms, there is a performance hit when running the precompiled scripts compared to runtime compilation on Android 4.3 due to more restrictions on compiler optimizations.

We’re really pleased with how the RenderScript Support Library has turned out. We've already seen how it performs in a shipping app — it's been part of the photo editor in the Google+ Android app since May 2013, and it’s definitely proven itself in a large and widely used application. We hope you’ll be happy with it too.

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RenderScript Intrinsics

Posted by R. Jason Sams, Android RenderScript Tech Lead

RenderScript has a very powerful ability called Intrinsics. Intrinsics are built-in functions that perform well-defined operations often seen in image processing. Intrinsics can be very helpful to you because they provide extremely high-performance implementations of standard functions with a minimal amount of code.

RenderScript intrinsics will usually be the fastest possible way for a developer to perform these operations. We’ve worked closely with our partners to ensure that the intrinsics perform as fast as possible on their architectures — often far beyond anything that can be achieved in a general-purpose language.

Table 1. RenderScript intrinsics and the operations they provide.

Name	Operation
ScriptIntrinsicConvolve3x3, ScriptIntrinsicConvolve5x5	Performs a 3x3 or 5x5 convolution.
ScriptIntrinsicBlur	Performs a Gaussian blur. Supports grayscale and RGBA buffers and is used by the system framework for drop shadows.
ScriptIntrinsicYuvToRGB	Converts a YUV buffer to RGB. Often used to process camera data.
ScriptIntrinsicColorMatrix	Applies a 4x4 color matrix to a buffer.
ScriptIntrinsicBlend	Blends two allocations in a variety of ways.
ScriptIntrinsicLUT	Applies a per-channel lookup table to a buffer.
ScriptIntrinsic3DLUT	Applies a color cube with interpolation to a buffer.

Your application can use one of these intrinsics with very little code. For example, to perform a Gaussian blur, the application can do the following:

RenderScript rs = RenderScript.create(theActivity);
ScriptIntrinsicBlur theIntrinsic = ScriptIntrinsicBlur.create(mRS, Element.U8_4(rs));;
Allocation tmpIn = Allocation.createFromBitmap(rs, inputBitmap);
Allocation tmpOut = Allocation.createFromBitmap(rs, outputBitmap);
theIntrinsic.setRadius(25.f);
theIntrinsic.setInput(tmpIn);
theIntrinsic.forEach(tmpOut);
tmpOut.copyTo(outputBitmap);

This example creates a RenderScript context and a Blur intrinsic. It then uses the intrinsic to perform a Gaussian blur with a 25-pixel radius on the allocation. The default implementation of blur uses carefully hand-tuned assembly code, but on some hardware it will instead use hand-tuned GPU code.

What do developers get from the tuning that we’ve done? On the new Nexus 7, running that same 25-pixel radius Gaussian blur on a 1.6 megapixel image takes about 176ms. A simpler intrinsic like the color matrix operation takes under 4ms. The intrinsics are typically 2-3x faster than a multithreaded C implementation and often 10x+ faster than a Java implementation. Pretty good for eight lines of code.

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Figure 1. Performance gains with RenderScript intrinsics, relative to equivalent multithreaded C implementations.

Applications that need additional functionality can mix these intrinsics with their own RenderScript kernels. An example of this would be an application that is taking camera preview data, converting it from YUV to RGB, adding a vignette effect, and uploading the final image to a SurfaceView for display.

In this example, we’ve got a stream of data flowing between a source device (the camera) and an output device (the display) with a number of possible processors along the way. Today, these operations can all run on the CPU, but as architectures become more advanced, using other processors becomes possible.

For example, the vignette operation can happen on a compute-capable GPU (like the ARM Mali T604 in the Nexus 10), while the YUV to RGB conversion could happen directly on the camera’s image signal processor (ISP). Using these different processors could significantly improve power consumption and performance. As more these processors become available, future Android updates will enable RenderScript to run on these processors, and applications written for RenderScript today will begin to make use of those processors transparently, without any additional work for developers.

Intrinsics provide developers a powerful tool they can leverage with minimal effort to achieve great performance across a wide variety of hardware. They can be mixed and matched with general purpose developer code allowing great flexibility in application design. So next time you have performance issues with image manipulation, I hope you give them a look to see if they can help.

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