page.title=3D Graphics parent.title=RenderScript parent.link=index.html @jd:body

In this document

  1. Developing a RenderScript application
    1. The Hello Graphics application

Related Samples

  1. Balls
  2. Fountain
  3. Hello World
  4. Samples

RenderScript provides a number of graphics APIs for 3D rendering, both at the Android framework level as well as at the native 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 lets you draw the actual meshes to render your scene. In general, you will need to be familiar with APIs to appropriately render 3D graphics on an Android-powered device.

Creating a Graphics RenderScript

Because of the various layers of code when writing a RenderScript application, it is useful to create the following files for a scene that you want to render:

The following sections describe how to implement these three classes by using the HelloWorld RenderScript sample that is provided in the SDK as a guide (some code has been modified from its original form for simplicity).

Creating the native RenderScript file

Your native RenderScript code resides in a .rs file in the <project_root>/src/ directory. You can also define .rsh header files. This code contains the logic to render your graphics and declares all necessary variables and pointers. Every graphics .rs file generally contains the following items:

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

#pragma version(1)

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

// Built-in header with graphics APIs
#include "rs_graphics.rsh"

// gTouchX and gTouchY are variables that are reflected for use
// by the Android framework API. This RenderScript uses them to be notified of touch events.
int gTouchX;
int gTouchY;

// This is invoked automatically when the script is created and initializes the variables
// in the Android framework layer as well.
void init() {
    gTouchX = 50.0f;
    gTouchY = 50.0f;
}

int root(int launchID) {

    // Clear the background color
    rsgClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    // Tell the runtime what the font color should be
    rsgFontColor(1.0f, 1.0f, 1.0f, 1.0f);
    // Introuduce ourselves to the world by drawing a greeting
    // at the position user touched on the screen
    rsgDrawText("Hello World!", gTouchX, gTouchY);

    // Return value tells RS roughly how often to redraw
    // in this case 20 ms
    return 20;
}

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. In this entry point class, you create a RenderScript object by instantiating a ScriptC_rs_filename and binding it to the RenderScript context. The RenderScript object is attached to the RenderScript bytecode, which is platform-independent and gets compiled on the device when the RenderScript application runs. Both the ScriptC_rs_filename class and bytecode is generated by the Android build tools and is packaged with the .apk file. The bytecode file is located in the <project_root>/res/raw/ directory and is named rs_filename.bc. You refer to the bytecode as a resource (R.raw.rs_filename). when creating the RenderScript object..

You then bind the RenderScript object to the RenderScript context, so that the surface view knows what code to use to render graphics. The following code shows how the HelloWorldRS class is implemented:

package com.android.rs.helloworld;

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

public class HelloWorldRS {
    //context and resources are obtained from RSSurfaceView, which calls init()
    private Resources mRes;
    private RenderScriptGL mRS;

    //Declare the RenderScript object
    private ScriptC_helloworld mScript;

    public HelloWorldRS() {
    }

    /**
     * This provides us with the RenderScript context and resources
     * that allow us to create the RenderScript object
     */
    public void init(RenderScriptGL rs, Resources res) {
        mRS = rs;
        mRes = res;
        initRS();
    }
    /**
     * Calls native RenderScript functions (set_gTouchX and set_gTouchY)
     * through the reflected layer class ScriptC_helloworld to pass in
     * touch point data.
     */
    public void onActionDown(int x, int y) {
        mScript.set_gTouchX(x);
        mScript.set_gTouchY(y);
    }
    /**
     * Binds the RenderScript object to the RenderScript context
     */
    private void initRS() {
        //create the RenderScript object
        mScript = new ScriptC_helloworld(mRS, mRes, R.raw.helloworld);
        //bind the RenderScript object to the RenderScript context
        mRS.bindRootScript(mScript);
    }
}

Creating the surface view

To create a surface view to render graphics on, create a class that extends {@link android.renderscript.RSSurfaceView}. This class also creates a RenderScript context object ({@link android.renderscript.RenderScriptGL} and passes it to the Rendscript entry point class to bind the two. The following code shows how the HelloWorldView class is implemented:

package com.android.rs.helloworld;

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

public class HelloWorldView extends RSSurfaceView {
    // RenderScript context
    private RenderScriptGL mRS;
    // RenderScript entry point object that does the rendering
    private HelloWorldRS mRender;

    public HelloWorldView(Context context) {
        super(context);
        initRS();
    }

    private void initRS() {
        if (mRS == null) {
            // Initialize RenderScript with default surface characteristics.
            RenderScriptGL.SurfaceConfig sc = new RenderScriptGL.SurfaceConfig();
            //Create the RenderScript context
            mRS = createRenderScriptGL(sc);
            // Create an instance of the RenderScript entry point class
            mRender = new HelloWorldRS();
            // Call the entry point class to bind it to this context
            mRender.init(mRS, getResources());
        }
    }

    /**
     * Rebind everything when the window becomes attached
     */
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        initRS();
    }

    /**
     * Stop rendering when window becomes detached
     */
    protected void onDetachedFromWindow() {
        // Handle the system event and clean up
        mRender = null;
        if (mRS != null) {
            mRS = null;
            destroyRenderScriptGL();
        }
    }

    /**
     * Use callbacks to relay data to RenderScript entry point class
     */
    public boolean onTouchEvent(MotionEvent ev) {
        // Pass touch events from the system to the rendering script
        if (ev.getAction() == MotionEvent.ACTION_DOWN) {
            mRender.onActionDown((int)ev.getX(), (int)ev.getY());
            return true;
        }

        return false;
    }
}

Creating the Activity

Applications that use RenderScript still adhere to activity lifecyle, and are part of the same view hierarchy as traditional Android applications, which is handled by the Android VM. This Activity class sets its view to be the {@link android.renderscript.RSSurfaceView} and handles lifecycle callback events appropriately. The following code shows how the HelloWorld class is implemented:

public class HelloWorldActivity extends Activity {

    //Custom view to use with RenderScript
    private HelloWorldView view;

    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        // Create surface view and set it as the content of our Activity
        mView = new HelloWorldView(this);
        setContentView(view);
    }

    protected void onResume() {
        // Ideally an app should implement onResume() and onPause()
        // to take appropriate action when the activity loses focus
        super.onResume();
        view.resume();
    }

    protected void onPause() {
        // Ideally an app should implement onResume() and onPause()
        // to take appropriate action when the activity loses focus
        super.onPause();
        view.pause();
    }
}

Drawing

Drawing using the rsgDraw functions

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

Drawing with a mesh

When you want to draw complex shapes and textures to the screen, instantiate a {@link android.renderscript.Mesh} and draw it to the screen with rsgDrawMesh(). A {@link android.renderscript.Mesh} is a collection of allocations that represent vertex data (positions, normals, texture coordinates) and index data such as triangles and lines. You can build a Mesh in three different ways:

To create a mesh using the {@link android.renderscript.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 {@link android.renderscript.Mesh.TriangleMeshBuilder#addTriangle addTriangle()} draws the triangle with vertex 0, 1, and 2 (the vertices are drawn counter-clockwise).

int float2VtxSize = 2;
Mesh.TriangleMeshBuilder triangle = 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 {@link android.renderscript.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 native 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.
}

Shaders

You can attach four program objects to the {@link android.renderscript.RenderScriptGL} context to customize the rendering pipeline. For example, you can create vertex and fragment shaders in GLSL or build a raster program object with provided methods without writing GLSL code. The four program objects mirror a traditional graphical rendering pipeline:

Android Object Type RenderScript Native Type Description
{@link android.renderscript.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 {@link android.renderscript.RenderScriptGL} graphics context by calling {@link android.renderscript.RenderScriptGL#bindProgramVertex 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 library 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 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 run-time would take care of connecting the two. Unlike OpenGL, there is no need to link the vertex and fragment programs.

To bind shader constructs to the Program, declare a struct containing the necessary shader constants in your native 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 system 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 native RenderScript code of the change.
{@link android.renderscript.ProgramFragment} rs_program_fragment

The RenderScript fragment program, also known as the 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, textures inputs, and a Type object describing 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 could 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 constants to this program, declare a struct containing the necessary shader constants in your native 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 system 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 native RenderScript code of the change.
{@link android.renderscript.ProgramStore} rs_program_store The RenderScript ProgramStore 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.
{@link android.renderscript.ProgramRaster} rs_program_raster Program raster 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 the RenderScript:

    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.

Shader bindings

You can also set four pragmas that control the shaders' default bindings to the {@link android.renderscript.RenderScriptGL} context when the script is executing:

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

("varying vec4 varColor;\n");
("varying vec2 varTex0;\n");
("void main() {\n");
(" gl_Position = UNI_MVP * ATTRIB_position;\n");
(" gl_PointSize = 1.0;\n");
(" varColor = ATTRIB_color;\n");
(" varTex0 = ATTRIB_texture0;\n");
("}\n");

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 {@link android.renderscript.RenderScriptGL} bind methods.

For example, you can define this at the top of your native graphics RenderScript code to have the Vertex and Store shaders inherent the bind properties from their parent scripts:

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

Defining a sampler

A {@link android.renderscript.Sampler} object defines how data is extracted from textures. Samplers are bound to Program objects (currently only a Fragment Program) 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 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.