Because applications that utilize RenderScript still run inside of the Android VM, you have access to all of the framework APIs that you are familiar with, but can utilize RenderScript when appropriate. To facilitate this interaction between the framework and the RenderScript runtime, an intermediate layer of code is also present to facilitate communication and memory management between the two levels of code. This document goes into more detail about these different layers of code as well as how memory is shared between the Android VM and RenderScript runtime.
RenderScript Runtime Layer
Your RenderScript code is compiled and executed in a compact and well-defined runtime layer. The RenderScript runtime APIs offer support for intensive computation that is portable and automatically scalable to the amount of cores available on a processor.
Note: The standard C functions in the NDK must be guaranteed to run on a CPU, so RenderScript cannot access these libraries, because RenderScript is designed to run on different types of processors.
You define your RenderScript code in
.rs
and
.rsh
files in the
src/
directory of your Android project. The code
is compiled to intermediate bytecode by the
llvm
compiler that runs as part of an Android build. When your application
runs on a device, the bytecode is then compiled (just-in-time) to machine code by another
llvm
compiler that resides on the device. The machine code is optimized for the
device and also cached, so subsequent uses of the RenderScript enabled application does not
recompile the bytecode.
Some key features of the RenderScript runtime libraries include:
- Memory allocation request features
- A large collection of math functions with both scalar and vector typed overloaded versions of many common routines. Operations such as adding, multiplying, dot product, and cross product are available as well as atomic arithmetic and comparison functions.
- Conversion routines for primitive data types and vectors, matrix routines, and date and time routines
- Data types and structures to support the RenderScript system such as Vector types for defining two-, three-, or four-vectors.
- Logging functions
See the RenderScript runtime API reference for more information on the available functions.
Reflected Layer
The reflected layer is a set of classes that the Android build tools generate to allow access to the RenderScript runtime from the Android framework. This layer also provides methods and constructors that allow you to allocate and work with memory for pointers that are defined in your RenderScript code. The following list describes the major components that are reflected:
-
Every
.rsfile that you create is generated into a class namedproject_root/gen/package/name/ScriptC_ renderscript_filenameof typeScriptC. This file is the.javaversion of your.rsfile, which you can call from the Android framework. This class contains the following items reflected from the.rsfile:- Non-static functions
-
Non-static, global RenderScript variables. Accessor methods are generated for each
variable, so you can read and write the RenderScript variables from the Android
framework. If a global variable is initialized at the RenderScript runtime layer, those
values are used to initialize the corresponding values in the Android framework layer. If global
variables are marked as
const, then asetmethod is not generated. - Global pointers
-
A
structis reflected into its own class namedproject_root/gen/package/name/ScriptField_struct_name, which extendsScript.FieldBase. This class represents an array of thestruct, which allows you to allocate memory for one or more instances of thisstruct.
Functions
Functions are reflected into the script class itself, located in
project_root/gen/package/name/ScriptC_renderscript_filename
. For
example, if you declare the following function in your RenderScript code:
void touch(float x, float y, float pressure, int id) {
if (id >= 10) {
return;
}
touchPos[id].x = x;
touchPos[id].y = y;
touchPressure[id] = pressure;
}
then the following code is generated:
public void invoke_touch(float x, float y, float pressure, int id) {
FieldPacker touch_fp = new FieldPacker(16);
touch_fp.addF32(x);
touch_fp.addF32(y);
touch_fp.addF32(pressure);
touch_fp.addI32(id);
invoke(mExportFuncIdx_touch, touch_fp);
}
Functions cannot have a return value, because the RenderScript system is designed to be asynchronous. When your Android framework code calls into RenderScript, the call is queued and is executed when possible. This restriction allows the RenderScript system to function without constant interruption and increases efficiency. If functions were allowed to have return values, the call would block until the value was returned.
If you want the RenderScript code to send a value back to the Android framework, use the
rsSendToClient()
function.
Variables
Variables of supported types are reflected into the script class itself, located in
project_root/gen/package/name/ScriptC_renderscript_filename
. A set of accessor
methods are generated for each variable. For example, if you declare the following variable in
your RenderScript code:
uint32_t unsignedInteger = 1;
then the following code is generated:
private long mExportVar_unsignedInteger;
public void set_unsignedInteger(long v){
mExportVar_unsignedInteger = v;
setVar(mExportVarIdx_unsignedInteger, v);
}
public long get_unsignedInteger(){
return mExportVar_unsignedInteger;
}
Structs
Structs are reflected into their own classes, located in
<project_root>/gen/com/example/renderscript/ScriptField_struct_name
. This
class represents an array of the
struct
and allows you to allocate memory for a
specified number of
struct
s. For example, if you declare the following struct:
typedef struct Point {
float2 position;
float size;
} Point_t;
then the following code is generated in
ScriptField_Point.java
:
package com.example.android.rs.hellocompute;
import android.renderscript.*;
import android.content.res.Resources;
/**
* @hide
*/
public class ScriptField_Point extends android.renderscript.Script.FieldBase {
static public class Item {
public static final int sizeof = 12;
Float2 position;
float size;
Item() {
position = new Float2();
}
}
private Item mItemArray[];
private FieldPacker mIOBuffer;
public static Element createElement(RenderScript rs) {
Element.Builder eb = new Element.Builder(rs);
eb.add(Element.F32_2(rs), "position");
eb.add(Element.F32(rs), "size");
return eb.create();
}
public ScriptField_Point(RenderScript rs, int count) {
mItemArray = null;
mIOBuffer = null;
mElement = createElement(rs);
init(rs, count);
}
public ScriptField_Point(RenderScript rs, int count, int usages) {
mItemArray = null;
mIOBuffer = null;
mElement = createElement(rs);
init(rs, count, usages);
}
private void copyToArray(Item i, int index) {
if (mIOBuffer == null) mIOBuffer = new FieldPacker(Item.sizeof * getType().getX()/* count
*/);
mIOBuffer.reset(index * Item.sizeof);
mIOBuffer.addF32(i.position);
mIOBuffer.addF32(i.size);
}
public void set(Item i, int index, boolean copyNow) {
if (mItemArray == null) mItemArray = new Item[getType().getX() /* count */];
mItemArray[index] = i;
if (copyNow) {
copyToArray(i, index);
mAllocation.setFromFieldPacker(index, mIOBuffer);
}
}
public Item get(int index) {
if (mItemArray == null) return null;
return mItemArray[index];
}
public void set_position(int index, Float2 v, boolean copyNow) {
if (mIOBuffer == null) mIOBuffer = new FieldPacker(Item.sizeof * getType().getX()/* count */);
if (mItemArray == null) mItemArray = new Item[getType().getX() /* count */];
if (mItemArray[index] == null) mItemArray[index] = new Item();
mItemArray[index].position = v;
if (copyNow) {
mIOBuffer.reset(index * Item.sizeof);
mIOBuffer.addF32(v);
FieldPacker fp = new FieldPacker(8);
fp.addF32(v);
mAllocation.setFromFieldPacker(index, 0, fp);
}
}
public void set_size(int index, float v, boolean copyNow) {
if (mIOBuffer == null) mIOBuffer = new FieldPacker(Item.sizeof * getType().getX()/* count */);
if (mItemArray == null) mItemArray = new Item[getType().getX() /* count */];
if (mItemArray[index] == null) mItemArray[index] = new Item();
mItemArray[index].size = v;
if (copyNow) {
mIOBuffer.reset(index * Item.sizeof + 8);
mIOBuffer.addF32(v);
FieldPacker fp = new FieldPacker(4);
fp.addF32(v);
mAllocation.setFromFieldPacker(index, 1, fp);
}
}
public Float2 get_position(int index) {
if (mItemArray == null) return null;
return mItemArray[index].position;
}
public float get_size(int index) {
if (mItemArray == null) return 0;
return mItemArray[index].size;
}
public void copyAll() {
for (int ct = 0; ct < mItemArray.length; ct++) copyToArray(mItemArray[ct], ct);
mAllocation.setFromFieldPacker(0, mIOBuffer);
}
public void resize(int newSize) {
if (mItemArray != null) {
int oldSize = mItemArray.length;
int copySize = Math.min(oldSize, newSize);
if (newSize == oldSize) return;
Item ni[] = new Item[newSize];
System.arraycopy(mItemArray, 0, ni, 0, copySize);
mItemArray = ni;
}
mAllocation.resize(newSize);
if (mIOBuffer != null) mIOBuffer = new FieldPacker(Item.sizeof * getType().getX()/* count */);
}
}
The generated code is provided to you as a convenience to allocate memory for structs requested
by the RenderScript runtime and to interact with
struct
s
in memory. Each
struct
's class defines the following methods and constructors:
-
Overloaded constructors that allow you to allocate memory. The
ScriptField_ struct_name (RenderScript rs, int count)constructor allows you to define the number of structures that you want to allocate memory for with thecountparameter. TheScriptField_ struct_name (RenderScript rs, int count, int usages)constructor defines an extra parameter,usages, that lets you specify the memory space of this memory allocation. There are four memory space possibilities:-
USAGE_SCRIPT: Allocates in the script memory space. This is the default memory space if you do not specify a memory space. -
USAGE_GRAPHICS_TEXTURE: Allocates in the texture memory space of the GPU. -
USAGE_GRAPHICS_VERTEX: Allocates in the vertex memory space of the GPU. -
USAGE_GRAPHICS_CONSTANTS: Allocates in the constants memory space of the GPU that is used by the various program objects.
You can specify multiple memory spaces by using the bitwise
ORoperator. Doing so notifies the RenderScript runtime that you intend on accessing the data in the specified memory spaces. The following example allocates memory for a custom data type in both the script and vertex memory spaces:ScriptField_Point touchPoints = new ScriptField_Point(myRenderScript, 2, Allocation.USAGE_SCRIPT | Allocation.USAGE_GRAPHICS_VERTEX); -
-
A static nested class,
Item, allows you to create an instance of thestruct, in the form of an object. This nested class is useful if it makes more sense to work with thestructin your Android code. When you are done manipulating the object, you can push the object to the allocated memory by callingset(Item i, int index, boolean copyNow)and setting theItemto the desired position in the array. The RenderScript runtime automatically has access to the newly written memory. -
Accessor methods to get and set the values of each field in a struct. Each of these
accessor methods have an
indexparameter to specify thestructin the array that you want to read or write to. Each setter method also has acopyNowparameter that specifies whether or not to immediately sync this memory to the RenderScript runtime. To sync any memory that has not been synced, callcopyAll(). -
The
createElement()method creates a description of the struct in memory. This description is used to allocate memory consisting of one or many elements. -
resize()works much like arealloc()in C, allowing you to expand previously allocated memory, maintaining the current values that were previously created. -
copyAll()synchronizes memory that was set on the framework level to the RenderScript runtime. When you call a set accessor method on a member, there is an optionalcopyNowboolean parameter that you can specify. Specifyingtruesynchronizes the memory when you call the method. If you specify false, you can callcopyAll()once, and it synchronizes memory for all the properties that are not yet synchronized.
Pointers
Pointers are reflected into the script class itself, located in
project_root/gen/package/name/ScriptC_renderscript_filename
. You
can declare pointers to a
struct
or any of the supported RenderScript types, but a
struct
cannot contain pointers or nested arrays. For example, if you declare the
following pointers to a
struct
and
int32_t
typedef struct Point {
float2 position;
float size;
} Point_t;
Point_t *touchPoints;
int32_t *intPointer;
then the following code is generated in:
private ScriptField_Point mExportVar_touchPoints;
public void bind_touchPoints(ScriptField_Point v) {
mExportVar_touchPoints = v;
if (v == null) bindAllocation(null, mExportVarIdx_touchPoints);
else bindAllocation(v.getAllocation(), mExportVarIdx_touchPoints);
}
public ScriptField_Point get_touchPoints() {
return mExportVar_touchPoints;
}
private Allocation mExportVar_intPointer;
public void bind_intPointer(Allocation v) {
mExportVar_intPointer = v;
if (v == null) bindAllocation(null, mExportVarIdx_intPointer);
else bindAllocation(v, mExportVarIdx_intPointer);
}
public Allocation get_intPointer() {
return mExportVar_intPointer;
}
A
get
method and a special method named
bind_
pointer_name
(instead of a
set()
method) is generated. This method allows you to bind the memory
that is allocated in the Android VM to the RenderScript runtime (you cannot allocate
memory in your
.rs
file). For more information, see
Working
with Allocated Memory
.
Memory Allocation APIs
Applications that use RenderScript still run in the Android VM. The actual RenderScript code, however, runs natively and
needs access to the memory allocated in the Android VM. To accomplish this, you must
attach the memory that is allocated in the VM to the RenderScript runtime. This
process, called binding, allows the RenderScript runtime to seamlessly work with memory that it
requests but cannot explicitly allocate. The end result is essentially the same as if you had
called
malloc
in C. The added benefit is that the Android VM can carry out garbage collection as well as
share memory with the RenderScript runtime layer. Binding is only necessary for dynamically allocated memory. Statically
allocated memory is automatically created for your RenderScript code at compile time. See
Figure 1
for more information on how memory allocation occurs.
To support this memory allocation system, there are a set of APIs that allow the Android VM to
allocate memory and offer similar functionality to a
malloc
call. These classes
essentially describe how memory should be allocated and also carry out the allocation. To better
understand how these classes work, it is useful to think of them in relation to a simple
malloc
call that can look like this:
array = (int *)malloc(sizeof(int)*10);
The
malloc
call can be broken up into two parts: the size of the memory being allocated (
sizeof(int)
),
along with how many units of that memory should be allocated (10). The Android framework provides classes for these two parts as
well as a class to represent
malloc
itself.
The
Element
class represents the (
sizeof(int)
) portion
of the
malloc
call and encapsulates one cell of a memory allocation, such as a single
float value or a struct. The
Type
class encapsulates the
Element
and the amount of elements to allocate (10 in our example). You can think of a
Type
as
an array of
Element
s. The
Allocation
class does the actual
memory allocation based on a given
Type
and represents the actual allocated memory.
In most situations, you do not need to call these memory allocation APIs directly. The reflected layer
classes generate code to use these APIs automatically and all you need to do to allocate memory is call a
constructor that is declared in one of the reflected layer classes and then bind
the resulting memory
Allocation
to the RenderScript.
There are some situations where you would want to use these classes directly to allocate memory on your
own, such as loading a bitmap from a resource or when you want to allocate memory for pointers to
primitive types. You can see how to do this in the
Allocating and binding memory to the RenderScript
section.
The following table describes the three memory management classes in more detail:
| Android Object Type | Description |
|---|---|
Element
|
An element describes one cell of a memory allocation and can have two forms: basic or complex.
A basic element contains a single component of data of any valid RenderScript data type.
Examples of basic element data types include a single
Complex elements contain a list of basic elements and are created from
|
Type
|
A type is a memory allocation template and consists of an element and one or more
dimensions. It describes the layout of the memory (basically an array of
A type consists of five dimensions: X, Y, Z, LOD (level of detail), and Faces (of a cube map). You can assign the X,Y,Z dimensions to any positive integer value within the constraints of available memory. A single dimension allocation has an X dimension of greater than zero while the Y and Z dimensions are zero to indicate not present. For example, an allocation of x=10, y=1 is considered two dimensional and x=10, y=0 is considered one dimensional. The LOD and Faces dimensions are booleans to indicate present or not present. |
Allocation
|
An allocation provides the memory for applications based on a description of the memory
that is represented by a
Allocation data is uploaded in one of two primary ways: type checked and type unchecked.
For simple arrays there are
|
Working with Memory
Non-static, global variables that you declare in your RenderScript are allocated memory at compile time.
You can work with these variables directly in your RenderScript code without having to allocate
memory for them at the Android framework level. The Android framework layer also has access to these variables
with the provided accessor methods that are generated in the reflected layer classes. If these variables are
initialized at the RenderScript runtime layer, those values are used to initialize the corresponding
values in the Android framework layer. If global variables are marked as const, then a
set
method is
not generated.
Note:
If you are using certain RenderScript structures that contain pointers, such as
rs_program_fragment
and
rs_allocation
, you have to obtain an object of the
corresponding Android framework class first and then call the
set
method for that
structure to bind the memory to the RenderScript runtime. You cannot directly manipulate these structures
at the RenderScript runtime layer. This restriction is not applicable to user-defined structures
that contain pointers, because they cannot be exported to a reflected layer class
in the first place. A compiler error is generated if you try to declare a non-static, global
struct that contains a pointer.
RenderScript also has support for pointers, but you must explicitly allocate the memory in your
Android framework code. When you declare a global pointer in your
.rs
file, you
allocate memory through the appropriate reflected layer class and bind that memory to the native
RenderScript layer. You can interact with this memory from the Android framework layer as well as
the RenderScript layer, which offers you the flexibility to modify variables in the most
appropriate layer.
Allocating and binding dynamic memory to the RenderScript
To allocate dynamic memory, you need to call the constructor of a
Script.FieldBase
class, which is the most common way. An alternative is to create an
Allocation
manually, which is required for things such as primitive type pointers. You should
use a
Script.FieldBase
class constructor whenever available for simplicity.
After obtaining a memory allocation, call the reflected
bind
method of the pointer to bind the allocated memory to the
RenderScript runtime.
The example below allocates memory for both a primitive type pointer,
intPointer
, and a pointer to a struct,
touchPoints
. It also binds the memory to the
RenderScript:
private RenderScript myRenderScript;
private ScriptC_example script;
private Resources resources;
public void init(RenderScript rs, Resources res) {
myRenderScript = rs;
resources = res;
//allocate memory for the struct pointer, calling the constructor
ScriptField_Point touchPoints = new ScriptField_Point(myRenderScript, 2);
//Create an element manually and allocate memory for the int pointer
intPointer = Allocation.createSized(myRenderScript, Element.I32(myRenderScript), 2);
//create an instance of the RenderScript, pointing it to the bytecode resource
mScript = new ScriptC_example(myRenderScript, resources, R.raw.example);
//bind the struct and int pointers to the RenderScript
mScript.bind_touchPoints(touchPoints);
script.bind_intPointer(intPointer);
...
}
Reading and writing to memory
You can read and write to statically and dynamically allocated memory both at the RenderScript runtime and Android framework layer.
Statically allocated memory comes with a one-way communication restriction
at the RenderScript runtime level. When RenderScript code changes the value of a variable, it is not
communicated back to the Android framework layer for efficiency purposes. The last value
that is set from the Android framework is always returned during a call to a
get
method. However, when Android framework code modifies a variable, that change can be communicated to
the RenderScript runtime automatically or synchronized at a later time. If you need to send data
from the RenderScript runtime to the Android framework layer, you can use the
rsSendToClient()
function
to overcome this limitation.
When working with dynamically allocated memory, any changes at the RenderScript runtime layer are propagated back to the Android framework layer if you modified the memory allocation using its associated pointer. Modifying an object at the Android framework layer immediately propagates that change back to the RenderScript runtime layer.
Reading and writing to global variables
Reading and writing to global variables is a straightforward process. You can use the accessor methods at the Android framework level or set them directly in the RenderScript code. Keep in mind that any changes that you make in your RenderScript code are not propagated back to the Android framework layer.
For example, given the following struct declared in a file named
rsfile.rs
:
typedef struct Point {
int x;
int y;
} Point_t;
Point_t point;
You can assign values to the struct like this directly in
rsfile.rs
. These values are not
propagated back to the Android framework level:
point.x = 1;
point.y = 1;
You can assign values to the struct at the Android framework layer like this. These values are propagated back to the RenderScript runtime level:
ScriptC_rsfile mScript;
...
Item i = new ScriptField_Point.Item();
i.x = 1;
i.y = 1;
mScript.set_point(i);
You can read the values in your RenderScript code like this:
rsDebug("Printing out a Point", point.x, point.y);
You can read the values in the Android framework layer with the following code. Keep in mind that this code only returns a value if one was set at the Android framework level. You will get a null pointer exception if you only set the value at the RenderScript runtime level:
Log.i("TAGNAME", "Printing out a Point: " + mScript.get_point().x + " " + mScript.get_point().y);
System.out.println(point.get_x() + " " + point.get_y());
Reading and writing global pointers
Assuming that memory has been allocated in the Android framework level and bound to the RenderScript runtime,
you can read and write memory from the Android framework level by using the
get
and
set
methods for that pointer.
In the RenderScript runtime layer, you can read and write to memory with pointers as normal and the changes are propagated
back to the Android framework layer, unlike with statically allocated memory.
For example, given the following pointer to a
struct
in a file named
rsfile.rs
:
typedef struct Point {
int x;
int y;
} Point_t;
Point_t *point;
Assuming you already allocated memory at the Android framework layer, you can access values in
the
struct
as normal. Any changes you make to the struct via its pointer variable
are automatically available to the Android framework layer:
point[index].x = 1;
point[index].y = 1;
You can read and write values to the pointer at the Android framework layer as well:
ScriptField_Point p = new ScriptField_Point(mRS, 1);
Item i = new ScriptField_Point.Item();
i.x=100;
i.y = 100;
p.set(i, 0, true);
mScript.bind_point(p);
points.get_x(0); //read x and y from index 0
points.get_x(0);
Once memory is already bound, you do not have to rebind the memory to the RenderScript runtime every time you make a change to a value.