Graphics

Renderscript provides a number of graphics APIs for rendering, both at the Android framework level as well as at the Renderscript runtime level. For instance, the Android framework APIs let you create meshes and define shaders to customize the graphical rendering pipeline. The native Renderscript graphics APIs let you draw the actual meshes to render your scene. You need to be familiar with both APIs to appropriately render graphics on an Android-powered device.

Creating a Graphics Renderscript

Renderscript applications require various layers of code, so it is useful to create the following files to help keep your application organized:

The Renderscript .rs file

This file contains the logic to do the graphics rendering.

The Renderscript entry point .java class

This class allows the view class to interact with the code defined in the .rs file. This class contains a Renderscript object (instance of ScriptC_renderscript_file), which allows your Android framework code to call the Renderscript code. In general, this class does much of the setup for Renderscript such as shader and mesh building and memory allocation and binding. The SDK samples follow the convention of naming this file ActivityRS.java, where Activity is the name of your main activity class.

The view .java class

This class extends RSSurfaceView or RSTextureView to provide a surface to render on. A RSSurfaceView consumes a whole window, but a RSTextureView allows you to draw Renderscript graphics inside of a view and add it to a ViewGroup alongside other views. In this class, you create a RenderScriptGL context object with a call to RSSurfaceView.createRenderscriptGL() or RSTextureView.createRenderscriptGL(). The RenderScriptGL context object contains information about the current rendering state of Renderscript such as the vertex and fragment shaders. You pass this context object to the Renderscript entry point class, so that class can modify the rendering context if needed and bind the Renderscript code to the context. Once bound, the view class can use the Renderscript code to display graphics. The view class should also implement callbacks for events inherited from View, such as onTouchEvent() and onKeyDown() if you want to detect these types of user interactions. The SDK samples follow the convention of naming this file ActivityView.java, where Activity is the name of your main activity class

The activity .java class

This class is the main activity class and sets your RSSurfaceView as the main content view for this activity or uses the RSTextureView alongside other views.

Figure 1 describes how these classes interact with one another in a graphics Renderscript:

Figure 1. Graphics Renderscript overview

The following sections describe how to create an application that uses a graphics Renderscript by using the Renderscript Fountain sample that is provided in the SDK as a guide (some code has been modified from its original form for simplicity).

Creating the Renderscript file

Your Renderscript code resides in .rs and .rsh (headers) files in the <project_root>/src/ directory. This code contains the logic to render your graphics and declares all other necessary items such as variables, structs, and pointers. Every graphics .rs file generally contains the following items:

• A pragma declaration (#pragma rs java_package_name(package.name)) that declares the package name of the .java reflection of this Renderscript.
• A pragma declaration (#pragma version(1)) that declares the version of Renderscript that you are using (1 is the only value for now).
• A #include "rs_graphics.rsh" declaration.
• A root() function. This is the main worker function for your Renderscript and calls Renderscript graphics functions to render scenes. This function is called every time a frame refresh occurs, which is specified as its return value. A 0 (zero) specified for the return value says to only render the frame when a property of the scene that you are rendering changes. A non-zero positive integer specifies the refresh rate of the frame in milliseconds.

  Note: The Renderscript runtime makes its best effort to refresh the frame at the specified rate. For example, if you are creating a live wallpaper and set the return value to 20, the Renderscript runtime renders the wallpaper at 50fps if it has just enough or more resources to do so. It renders as fast as it can if not enough resources are available.

  For more information on using the Renderscript graphics functions, see the Drawing section.

• An init() function. This allows you to do initialization of your Renderscript before the root() function runs, such as assigning values to variables. This function runs once and is called automatically when the Renderscript starts, before anything else in your Renderscript. Creating this function is optional.
• Any variables, pointers, and structures that you wish to use in your Renderscript code (can be declared in .rsh files if desired)

The following code shows how the fountain.rs file is implemented:

#pragma version(1)

// Tell which java package name the reflected files should belong to
#pragma rs java_package_name(com.example.android.rs.fountain)

//declare shader binding
#pragma stateFragment(parent)

// header with graphics APIs, must include explicitly
#include "rs_graphics.rsh"

static int newPart = 0;

// the mesh to render
rs_mesh partMesh;

// the point representing where a particle is rendered
typedef struct __attribute__((packed, aligned(4))) Point {
    float2 delta;
    float2 position;
    uchar4 color;
} Point_t;
Point_t *point;

// main worker function that renders particles onto the screen
int root() {
    float dt = min(rsGetDt(), 0.1f);
    rsgClearColor(0.f, 0.f, 0.f, 1.f);
    const float height = rsgGetHeight();
    const int size = rsAllocationGetDimX(rsGetAllocation(point));
    float dy2 = dt * (10.f);
    Point_t * p = point;
    for (int ct=0; ct < size; ct++) {
        p->delta.y += dy2;
        p->position += p->delta;
        if ((p->position.y > height) && (p->delta.y > 0)) {
            p->delta.y *= -0.3f;
        }
        p++;
    }

    rsgDrawMesh(partMesh);
    return 1;
}

// adds particles to the screen to render
static float4 partColor[10];
void addParticles(int rate, float x, float y, int index, bool newColor)
{
    if (newColor) {
        partColor[index].x = rsRand(0.5f, 1.0f);
        partColor[index].y = rsRand(1.0f);
        partColor[index].z = rsRand(1.0f);
    }
    float rMax = ((float)rate) * 0.02f;
    int size = rsAllocationGetDimX(rsGetAllocation(point));
    uchar4 c = rsPackColorTo8888(partColor[index]);

    Point_t * np = &point[newPart];
    float2 p = {x, y};
    while (rate--) {
        float angle = rsRand(3.14f * 2.f);
        float len = rsRand(rMax);
        np->delta.x = len * sin(angle);
        np->delta.y = len * cos(angle);
        np->position = p;
        np->color = c;
        newPart++;
        np++;
        if (newPart >= size) {
            newPart = 0;
            np = &point[newPart];
        }
    }
}

Creating the Renderscript entry point class

When you create a Renderscript (.rs) file, it is helpful to create a corresponding Android framework class that is an entry point into the .rs file. The most important thing this class does is receive a RenderScriptGL rendering context object from the view class and binds the actual Renderscript code to the rendering context. This notifies your view class of the code that it needs to render graphics.

In addition, this class should contain all of the things needed to set up Renderscript. Some important things that you need to do in this class are:

• Create a Renderscript object ScriptC_rs_filename. The Renderscript object is attached to the Renderscript bytecode, which is platform-independent and gets compiled on the device when the Renderscript application runs. The bytecode is referenced as a raw resource and is passed into the constructor for the Renderscript object. For example, this is how the Fountain sample creates the Renderscript object:

    RenderScriptGL rs;  //obtained from the view class
    Resources res;      //obtained from the view class
    ...
    ScriptC_fountain mScript = new ScriptC_fountain(mRS, mRes, R.raw.fountain);
    

• Allocate any necessary memory and bind it to your Renderscript code via the Renderscript object.
• Build any necessary meshes and bind them to the Renderscript code via the Renderscript object.
• Create any necessary programs and bind them to the Renderscript code via the Renderscript object.

The following code shows how the FountainRS class is implemented:

package com.example.android.rs.fountain;

import android.content.res.Resources;
import android.renderscript.*;
import android.util.Log;

public class FountainRS {
    public static final int PART_COUNT = 50000;

    public FountainRS() {
    }

    /**
     * This provides us with the Renderscript context and resources
     * that allow us to create the Renderscript object
     */
    private Resources mRes;
    private RenderScriptGL mRS;

    // Renderscript object
    private ScriptC_fountain mScript;

    // Called by the view class to initialize the Renderscript context and renderer
    public void init(RenderScriptGL rs, Resources res) {
        mRS = rs;
        mRes = res;

        /**
         * Create a shader and bind to the Renderscript context
         */
        ProgramFragmentFixedFunction.Builder pfb = new ProgramFragmentFixedFunction.Builder(rs);
        pfb.setVaryingColor(true);
        rs.bindProgramFragment(pfb.create());

        /**
         * Allocate memory for the particles to render and create the mesh to draw
         */
        ScriptField_Point points = new ScriptField_Point(mRS, PART_COUNT);
        Mesh.AllocationBuilder smb = new Mesh.AllocationBuilder(mRS);
        smb.addVertexAllocation(points.getAllocation());
        smb.addIndexSetType(Mesh.Primitive.POINT);
        Mesh sm = smb.create();

       /**
        * Create and bind the Renderscript object to the Renderscript context
        */
        mScript = new ScriptC_fountain(mRS, mRes, R.raw.fountain);
        mScript.set_partMesh(sm);
        mScript.bind_point(points);
        mRS.bindRootScript(mScript);
    }

    boolean holdingColor[] = new boolean[10];

    /**
     * Calls Renderscript functions (invoke_addParticles)
     * via the Renderscript object to add particles to render
     * based on where a user touches the screen.
     */
    public void newTouchPosition(float x, float y, float pressure, int id) {
        if (id >= holdingColor.length) {
            return;
        }
        int rate = (int)(pressure * pressure * 500.f);
        if (rate > 500) {
            rate = 500;
        }
        if (rate > 0) {
            mScript.invoke_addParticles(rate, x, y, id, !holdingColor[id]);
            holdingColor[id] = true;
        } else {
            holdingColor[id] = false;
        }

    }
}

Creating the view class

To display graphics, you need a view to render on. Create a class that extends RSSurfaceView or RSTextureView. This class allows you to create a RenderScriptGL context object by calling and pass it to the Rendscript entry point class to bind the two. Once bound, the content is aware of the code that it needs to use to render graphics with. If your Renderscript code depends on any type of information that the view is aware of, such as touches from the user, you can also use this class to relay that information to the Renderscript entry point class. The following code shows how the FountainView class is implemented:

package com.example.android.rs.fountain;

import android.renderscript.RSTextureView;
import android.renderscript.RenderScriptGL;
import android.content.Context;
import android.view.MotionEvent;

public class FountainView extends RSTextureView {

    public FountainView(Context context) {
        super(context);
    }
    // Renderscript context
    private RenderScriptGL mRS;
    // Renderscript entry point object that calls Renderscript code
    private FountainRS mRender;

    /**
     * Create Renderscript context and initialize Renderscript entry point
     */
    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        android.util.Log.e("rs", "onAttachedToWindow");
        if (mRS == null) {
            RenderScriptGL.SurfaceConfig sc = new RenderScriptGL.SurfaceConfig();
            mRS = createRenderScriptGL(sc);
            mRender = new FountainRS();
            mRender.init(mRS, getResources());
        }
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        android.util.Log.e("rs", "onDetachedFromWindow");
        if (mRS != null) {
            mRS = null;
            destroyRenderScriptGL();
        }
    }


    /**
     * Use callbacks to relay data to Renderscript entry point class
     */
    @Override
    public boolean onTouchEvent(MotionEvent ev)
    {
        int act = ev.getActionMasked();
        if (act == ev.ACTION_UP) {
            mRender.newTouchPosition(0, 0, 0, ev.getPointerId(0));
            return false;
        } else if (act == MotionEvent.ACTION_POINTER_UP) {
            // only one pointer going up, we can get the index like this
            int pointerIndex = ev.getActionIndex();
            int pointerId = ev.getPointerId(pointerIndex);
            mRender.newTouchPosition(0, 0, 0, pointerId);
        }
        int count = ev.getHistorySize();
        int pcount = ev.getPointerCount();

        for (int p=0; p < pcount; p++) {
            int id = ev.getPointerId(p);
            mRender.newTouchPosition(ev.getX(p),
                                     ev.getY(p),
                                     ev.getPressure(p),
                                     id);

            for (int i=0; i < count; i++) {
                mRender.newTouchPosition(ev.getHistoricalX(p, i),
                                         ev.getHistoricalY(p, i),
                                         ev.getHistoricalPressure(p, i),
                                         id);
            }
        }
        return true;
    }
}

Creating the activity class

Applications that use Renderscript still behave like normal Android applications, so you need an activity class that handles activity lifecycle callback events appropriately. The activity class also sets your RSSurfaceView view class to be the main content view of the activity or uses your RSTextureView in a ViewGroup alongside other views.

The following code shows how the Fountain sample declares its activity class:

package com.example.android.rs.fountain;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;

public class Fountain extends Activity {

    private static final String LOG_TAG = "libRS_jni";
    private static final boolean DEBUG  = false;
    private static final boolean LOG_ENABLED = false;

    private FountainView mView;

    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);

        // Create our Preview view and set it as 
        // the content of our activity
        mView = new FountainView(this);
        setContentView(mView);
    }

    @Override
    protected void onResume() {
        Log.e("rs", "onResume");

        // Ideally a game should implement onResume() and onPause()
        // to take appropriate action when the activity looses focus
        super.onResume();
        mView.resume();
    }

    @Override
    protected void onPause() {
        Log.e("rs", "onPause");

        // Ideally a game should implement onResume() and onPause()
        // to take appropriate action when the activity looses focus
        super.onPause();
        mView.pause();

    }

    static void log(String message) {
        if (LOG_ENABLED) {
            Log.v(LOG_TAG, message);
        }
    }
}

Now that you have an idea of what is involved in a Renderscript graphics application, you can start building your own. It might be easiest to begin with one of the Renderscript samples as a starting point if this is your first time using Renderscript.

Drawing

The following sections describe how to use the graphics functions to draw with Renderscript.

Simple drawing

The native Renderscript APIs provide a few convenient functions to easily draw a polygon or text to the screen. You call these in your root() function to have them render to the RSSurfaceView or RSTextureView. These functions are available for simple drawing and should not be used for complex graphics rendering:

• rsgDrawRect(): Sets up a mesh and draws a rectangle to the screen. It uses the top left vertex and bottom right vertex of the rectangle to draw.
• rsgDrawQuad(): Sets up a mesh and draws a quadrilateral to the screen.
• rsgDrawQuadTexCoords(): Sets up a mesh and draws a quadrilateral to the screen using the provided coordinates of a texture.
• rsgDrawText(): Draws specified text to the screen. Use rsgFontColor() to set the color of the text.

Drawing with a mesh

When you want to render complex scenes to the screen, instantiate a Mesh and draw it with rsgDrawMesh(). A Mesh is a collection of allocations that represent vertex data (positions, normals, texture coordinates) and index data that provides information on how to draw triangles and lines with the provided vertex data. You can build a Mesh in three different ways:

• Build the mesh with the Mesh.TriangleMeshBuilder class, which allows you to specify a set of vertices and indices for each triangle that you want to draw.
• Build the mesh using an Allocation or a set of Allocations with the Mesh.AllocationBuilder class. This approach allows you to build a mesh with vertices already stored in memory, which allows you to specify the vertices in Renderscript or Android framework code.
• Build the mesh with the Mesh.Builder class. You should use this convenience method when you know the data types you want to use to build your mesh, but don't want to make separate memory allocations like with Mesh.AllocationBuilder. You can specify the types that you want and this mesh builder automatically creates the memory allocations for you.

To create a mesh using the Mesh.TriangleMeshBuilder, you need to supply it with a set of vertices and the indices for the vertices that comprise the triangle. For example, the following code specifies three vertices, which are added to an internal array, indexed in the order they were added. The call to addTriangle() draws the triangle with vertex 0, 1, and 2 (the vertices are drawn counter-clockwise).

int float2VtxSize = 2;
Mesh.TriangleMeshBuilder triangles = new Mesh.TriangleMeshBuilder(renderscriptGL,
float2VtxSize, Mesh.TriangleMeshBuilder.COLOR);
triangles.addVertex(300.f, 300.f);
triangles.addVertex(150.f, 450.f);
triangles.addVertex(450.f, 450.f);
triangles.addTriangle(0 , 1, 2);
Mesh smP = triangle.create(true);
script.set_mesh(smP);

To draw a mesh using the Mesh.AllocationBuilder, you need to supply it with one or more allocations that contain the vertex data:

Allocation vertices;

...
Mesh.AllocationBuilder triangle = new Mesh.AllocationBuilder(mRS);
smb.addVertexAllocation(vertices.getAllocation());
smb.addIndexSetType(Mesh.Primitive.TRIANGLE);
Mesh smP = smb.create();
script.set_mesh(smP);

In your Renderscript code, draw the built mesh to the screen:

rs_mesh mesh;
...

int root(){
...
rsgDrawMesh(mesh);
...
return 0; //specify a non zero, positive integer to specify the frame refresh.
          //0 refreshes the frame only when the mesh changes.
}

Programs

You can attach four program objects to the RenderScriptGL context to customize the rendering pipeline. For example, you can create vertex and fragment shaders in GLSL or build a raster program object that controls culling. The four programs mirror a traditional graphical rendering pipeline:

Android Object Type	Renderscript Native Type	Description
ProgramVertex	rs_program_vertex	The Renderscript vertex program, also known as a vertex shader, describes the stage in the graphics pipeline responsible for manipulating geometric data in a user-defined way. The object is constructed by providing Renderscript with the following data: An Element describing its varying inputs or attributes GLSL shader string that defines the body of the program a Type that describes the layout of an Allocation containing constant or uniform inputs Once the program is created, bind it to the RenderScriptGL graphics context by calling bindProgramVertex(). It is then used for all subsequent draw calls until you bind a new program. If the program has constant inputs, the user needs to bind an allocation containing those inputs. The allocation's type must match the one provided during creation. The Renderscript runtime then does all the necessary plumbing to send those constants to the graphics hardware. Varying inputs to the shader, such as position, normal, and texture coordinates are matched by name between the input Element and the mesh object that is being drawn. The signatures don't have to be exact or in any strict order. As long as the input name in the shader matches a channel name and size available on the mesh, the Renderscript runtime handles connecting the two. Unlike OpenGL there is no need to link the vertex and fragment programs. To bind shader constants to the program, declare a struct that contains the necessary shader constants in your Renderscript code. This struct is generated into a reflected class that you can use as a constant input element during the program's creation. It is an easy way to create an instance of this struct as an allocation. You would then bind this Allocation to the program and the Renderscript runtime sends the data that is contained in the struct to the hardware when necessary. To update shader constants, you change the values in the Allocation and notify the Renderscript code of the change. The ProgramVertexFixedFunction.Builder class also lets you build a simple vertex shader without writing GLSL code.
ProgramFragment	rs_program_fragment	The Renderscript fragment program, also known as a fragment shader, is responsible for manipulating pixel data in a user-defined way. It's constructed from a GLSL shader string containing the program body, texture inputs, and a Type object that describes the constants used by the program. Like the vertex programs, when an Allocation with constant input values is bound to the shader, its values are sent to the graphics program automatically. Note that the values inside the Allocation are not explicitly tracked. If they change between two draw calls using the same program object, notify the runtime of that change by calling rsgAllocationSyncAll(), so it can send the new values to hardware. Communication between the vertex and fragment programs is handled internally in the GLSL code. For example, if the fragment program is expecting a varying input called varTex0, the GLSL code inside the program vertex must provide it. To bind shader constructs to the program, declare a struct that contains the necessary shader constants in your Renderscript code. This struct is generated into a reflected class that you can use as a constant input element during the program's creation. It is an easy way to create an instance of this struct as an allocation. You would then bind this Allocation to the program and the Renderscript runtime sends the data that is contained in the struct to the hardware when necessary. To update shader constants, you change the values in the Allocation and notify the Renderscript code of the change. The ProgramFragmentFixedFunction.Builder class also lets you build a simple fragment shader without writing GLSL code.
ProgramStore	rs_program_store	The Renderscript store program contains a set of parameters that control how the graphics hardware writes to the framebuffer. It could be used to enable and disable depth writes and testing, setup various blending modes for effects like transparency and define write masks for color components.
ProgramRaster	rs_program_raster	The Renderscript raster program is primarily used to specify whether point sprites are enabled and to control the culling mode. By default back faces are culled.

The following example defines a vertex shader in GLSL and binds it to a Renderscript context object:

    private RenderScriptGL glRenderer;      //rendering context
    private ScriptField_Point mPoints;      //vertices
    private ScriptField_VpConsts mVpConsts; //shader constants

    ...

     ProgramVertex.Builder sb = new ProgramVertex.Builder(glRenderer);
        String t =  "varying vec4 varColor;\n" +
                    "void main() {\n" +
                    "  vec4 pos = vec4(0.0, 0.0, 0.0, 1.0);\n" +
                    "  pos.xy = ATTRIB_position;\n" +
                    "  gl_Position = UNI_MVP * pos;\n" +
                    "  varColor = vec4(1.0, 1.0, 1.0, 1.0);\n" +
                    "  gl_PointSize = ATTRIB_size;\n" +
                    "}\n";
        sb.setShader(t);
        sb.addConstant(mVpConsts.getType());
        sb.addInput(mPoints.getElement());
        ProgramVertex pvs = sb.create();
        pvs.bindConstants(mVpConsts.getAllocation(), 0);
        glRenderer.bindProgramVertex(pvs);

The RsRenderStatesRS sample has many examples on how to create a shader without writing GLSL.

Program bindings

You can also declare four pragmas that control default program bindings to the RenderScriptGL context when the script is executing:

• stateVertex
• stateFragment
• stateRaster
• stateStore

The possible values for each pragma are parent or default. Using default binds the shaders to the graphical context with the system defaults.

Using parent binds the shaders in the same manner as it is bound in the calling script. If this is the root script, the parent state is taken from the bind points that are set by the RenderScriptGL bind methods.

For example, you can define this at the top of your graphics Renderscript code to have the vertex and store programs inherent the bind properties from their parent scripts:

#pragma stateVertex(parent)
#pragma stateStore(parent)

Defining a sampler

A Sampler object defines how data is extracted from textures. Samplers are bound to a ProgramFragment alongside the texture whose sampling they control. These objects are used to specify such things as edge clamping behavior, whether mip-maps are used, and the amount of anisotropy required. There might be situations where hardware does not support the desired behavior of the sampler. In these cases, the Renderscript runtime attempts to provide the closest possible approximation. For example, the user requested 16x anisotropy, but only 8x was set because it's the best available on the hardware.

The RsRenderStatesRS sample has many examples on how to create a sampler and bind it to a Fragment program.

Rendering to a Framebuffer Object

Framebuffer objects allow you to render offscreen instead of in the default onscreen framebuffer. This approach might be useful for situations where you need to post-process a texture before rendering it to the screen, or when you want to composite two scenes in one such as rendering a rear-view mirror of a car. There are two buffers associated with a framebuffer object: a color buffer and a depth buffer. The color buffer (required) contains the actual pixel data of the scene that you are rendering, and the depth buffer (optional) contains the values necessary to figure out what vertices are drawn depending on their z-values.

In general, you need to do the following to render to a framebuffer object:

• Create Allocation objects for the color buffer and depth buffer (if needed). Specify the USAGE_GRAPHICS_RENDER_TARGET usage attribute for these allocations to notify the Renderscript runtime to use these allocations for the framebuffer object. For the color buffer allocation, you most likely need to declare the USAGE_GRAPHICS_TEXTURE usage attribute to use the color buffer as a texture, which is the most common use of the framebuffer object.
• Tell the Renderscript runtime to render to the framebuffer object instead of the default framebuffer by calling rsgBindColorTarget() and passing it the color buffer allocation. If applicable, call rsgBindDepthTarget() passing in the depth buffer allocation as well.
• Render your scene normally with the rsgDraw functions. The scene will be rendered into the color buffer instead of the default onscreen framebuffer.
• When done, tell the Renderscript runtime stop rendering to the color buffer and back to the default framebuffer by calling rsgClearAllRenderTargets().
• Create a fragment shader and bind a the color buffer to it as a texture.
• Render your scene to the default framebuffer. The texture will be used according to the way you setup your fragment shader.

The following example shows you how to render to a framebuffer object by modifying the Fountain Renderscript sample. The end result is the FountainFBO sample. The modifications render the exact same scene into a framebuffer object as it does the default framebuffer. The framebuffer object is then rendered into the default framebuffer in a small area at the top left corner of the screen.

1. Modify fountain.rs and add the following global variables. This creates setter methods when this file is reflected into a .java file, allowing you to allocate memory in your Android framework code and binding it to the Renderscript runtime.

   //allocation for color buffer
   rs_allocation gColorBuffer;
   //fragment shader for rendering without a texture (used for rendering to framebuffer object)
   rs_program_fragment gProgramFragment;
   //fragment shader for rendering with a texture (used for rendering to default framebuffer)
   rs_program_fragment gTextureProgramFragment;
   

2. Modify the root function of fountain.rs to look like the following code. The modifications are commented:

   int root() {
       float dt = min(rsGetDt(), 0.1f);
       rsgClearColor(0.f, 0.f, 0.f, 1.f);
       const float height = rsgGetHeight();
       const int size = rsAllocationGetDimX(rsGetAllocation(point));
       float dy2 = dt * (10.f);
       Point_t * p = point;
       for (int ct=0; ct < size; ct++) {
           p->delta.y += dy2;
           p->position += p->delta;
           if ((p->position.y > height) && (p->delta.y > 0)) {
               p->delta.y *= -0.3f;
           }
           p++;
       }
       //Tell Renderscript runtime to render to the frame buffer object
       rsgBindColorTarget(gColorBuffer, 0);
       //Begin rendering on a white background
       rsgClearColor(1.f, 1.f, 1.f, 1.f);
       rsgDrawMesh(partMesh);
   
       //When done, tell Renderscript runtime to stop rendering to framebuffer object
       rsgClearAllRenderTargets();
   
       //Bind a new fragment shader that declares the framebuffer object to be used as a texture
       rsgBindProgramFragment(gTextureProgramFragment);
   
       //Bind the framebuffer object to the fragment shader at slot 0 as a texture
       rsgBindTexture(gTextureProgramFragment, 0, gColorBuffer);
       //Draw a quad using the framebuffer object as the texture
       float startX = 10, startY = 10;
       float s = 256;
       rsgDrawQuadTexCoords(startX, startY, 0, 0, 1,
                            startX, startY + s, 0, 0, 0,
                            startX + s, startY + s, 0, 1, 0,
                            startX + s, startY, 0, 1, 1);
   
       //Rebind the original fragment shader to render as normal
       rsgBindProgramFragment(gProgramFragment);
   
       //Render the main scene
       rsgDrawMesh(partMesh);
   
       return 1;
   }
   

3. In the FountainRS.java file, modify the init() method to look like the following code. The modifications are commented:

   /* Add necessary members */
   private ScriptC_fountainfbo mScript;
   private Allocation mColorBuffer;
   private ProgramFragment mProgramFragment;
   private ProgramFragment mTextureProgramFragment;
   
   public void init(RenderScriptGL rs, Resources res) {
       mRS = rs;
       mRes = res;
   
       ScriptField_Point points = new ScriptField_Point(mRS, PART_COUNT);
   
       Mesh.AllocationBuilder smb = new Mesh.AllocationBuilder(mRS);
       smb.addVertexAllocation(points.getAllocation());
       smb.addIndexSetType(Mesh.Primitive.POINT);
       Mesh sm = smb.create();
   
       mScript = new ScriptC_fountainfbo(mRS, mRes, R.raw.fountainfbo);
       mScript.set_partMesh(sm);
       mScript.bind_point(points);
   
       ProgramFragmentFixedFunction.Builder pfb = new ProgramFragmentFixedFunction.Builder(rs);
       pfb.setVaryingColor(true);
       mProgramFragment = pfb.create();
       mScript.set_gProgramFragment(mProgramFragment);
   
       /* Second fragment shader to use a texture (framebuffer object) to draw with */
       pfb.setTexture(ProgramFragmentFixedFunction.Builder.EnvMode.REPLACE,
           ProgramFragmentFixedFunction.Builder.Format.RGBA, 0);
   
       /* Set the fragment shader in the Renderscript runtime */
       mTextureProgramFragment = pfb.create();
       mScript.set_gTextureProgramFragment(mTextureProgramFragment);
   
       /* Create the allocation for the color buffer */
       Type.Builder colorBuilder = new Type.Builder(mRS, Element.RGBA_8888(mRS));
       colorBuilder.setX(256).setY(256);
       mColorBuffer = Allocation.createTyped(mRS, colorBuilder.create(),
       Allocation.USAGE_GRAPHICS_TEXTURE |
       Allocation.USAGE_GRAPHICS_RENDER_TARGET);
   
       /* Set the allocation in the Renderscript runtime */
       mScript.set_gColorBuffer(mColorBuffer);
   
       mRS.bindRootScript(mScript);
   }
   

   Note: This sample doesn't use a depth buffer, but the following code shows you how to declare an example depth buffer if you need to use one for your application. The depth buffer must have the same dimensions as the color buffer:

   Allocation mDepthBuffer;
   
   ...
   
   Type.Builder b = new Type.Builder(mRS, Element.createPixel(mRS, DataType.UNSIGNED_16,
       DataKind.PIXEL_DEPTH));
   b.setX(256).setY(256);
   mDepthBuffer = Allocation.createTyped(mRS, b.create(),
   Allocation.USAGE_GRAPHICS_RENDER_TARGET);
   
   

4. Run and use the sample. The smaller, white quad on the top-left corner is using the framebuffer object as a texture, which renders the same scene as the main rendering.