Introduction To OpenGLES in Android

OpenGLES

● Graphics Library for 3D

OpenGLES Terms

● OpenGLES : Graphics API for doing 3D operations on GPU / CPU

● Primitives : lines, point, triangles

● Texture : make the image

realistic by adding bitmap

CPU versus GPU

● CPU – good at executing sequential code

– Handles branches well

● GPU– Same code, multiple data

– Parallelism (ideal for image rendering)

Android Graphics

● The View class handles display and interaction with the user

● GLSurfaceView class provides the glue to connect OpenGLES to View system and activity lifecycle

View

● Manages the memory that can be composited into the Android view system

● Renders display in a separate thread, decoupling from UI thread

Renderer

● The renderer is responsible for making OpenGL calls to render a frame.

Two Steps

GLSurfaceViewGLSurfaceView.Renderer

GLSurfaceView    

    GLSurfaceView view = new GLSurfaceView(this);

    view.setEGLContextClientVersion(2);

    view.setRenderer(new SquareRenderer());

GLSurfaceView.Renderer

● The renderer is responsible for making OpenGL calls to render a frame. – onDrawFrame() responsible for drawing the

current frame

– OnSurfaceChanged() called when surface size changes

– OnSurfaceCreated() called when surface is created

GLSurfaceView.Renderer

public class SquareRenderer implements GLSurfaceView.Renderer {

    public void onSurfaceCreated(GL10 unused, EGLConfig config) {              }    public void onDrawFrame(GL10 unused) {

    }    public void onSurfaceChanged(GL10 unused, int width, int height)   {

           }}

GLES20.glViewport(0, 0, width, height);

GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT);

 GLES20.glClearColor(0.5f, 0.5f, 0.5f, 1.0f);

Make sure to add this!

Drawing a Basic Shape

Define a Square

• All the 2D/ 3D objects needs to be defined using Primitives.

• Vertex - A vertex is a point where two or more edges meet

• Edges - A vertex (vertices in plural) is the smallest building block of 3D model. A vertex is a point where two or more edges meet

• Face is a triangle. Face is a surface between three corner vertices and three surrounding edges.

-0.5f, -0.5f, 0.0f, // Bottom Left0.5f, -0.5f, 0.0f, // Bottom Right-0.5f, 0.5f, 0.0f, // Top Left0.5f, 0.5f, 0.0f, // Top Right

private void initShapes(){ float squareCoords[] = {   //The coordinates     };

  // initialize vertex Buffer for square ByteBuffer vbb = ByteBuffer.allocateDirect(squareCoords.length * 4);

  vbb.order(ByteOrder.nativeOrder());  squareVB = vbb.asFloatBuffer();   squareVB.put(squareCoords);   squareVB.position(0);}

Draw Methods o glDrawArrays()o glDrawElements()

Available Primitives in OpenGL ES

• GL_POINTS• GL_LINE_STRIP• GL_LINE_LOOP• GL_LINES• GL_TRIANGLES• GL_TRIANGLE_STRIP• GL_TRIANGLE_FAN

Draw a square

GL_POINTS GL_LINES GL_LINE_STRIP

GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN

OpenGL Rendering Pipeline Simplified

Shader Programs

• Vertex Shader• Fragment Shader• Loading the shader objects• Attaching the Shader objects to Shader program• Linking the program to create executable shader

program

Vertex Shader

    

Fragment Shader

   

attribute vec4 vertexPosition;void main(){  gl_Position = vertexPosition;

}

precision mediump float;void main(){ gl_FragColor = vec4(0.5, 0.5, 0.5, 1.0);}

Loading the Shader

GLES20.glCompileShader(vertexShader);

• GLES20.GL_FRAGMENT_SHADER

int vertexShader =           GLES20.glCreateShader(GLES20.GL_VERTEX_SHADER);

GLES20.glShaderSource(vertexShader, shaderCode);

Compiling and Linking the Shader program

shaderProgram = GLES20.glCreateProgram();

GLES20.glAttachShader(shaderProgram, vertexShader); GLES20.glAttachShader(shaderProgram, fragmentShader);

GLES20.glLinkProgram(shaderProgram);

attributePositionHandle =     GLES20.glGetAttribLocation(shaderProgram,"vertexPosition");

Drawing the square

GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT);

GLES20.glUseProgram(shaderProgram);

GLES20.glVertexAttribPointer(attributePositionHandle,                              3, GLES20.GL_FLOAT, false, 12, squareVB);

GLES20.glEnableVertexAttribArray(attributePositionHandle);

GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);