The document introduces OpenGL ES for 3D graphics in Android, explaining its role as a graphics API for GPU and CPU operations, including basic concepts like primitives and textures. It highlights the functionality of the GLSurfaceView class and the responsibilities of the renderer in rendering frames and handling surface changes. Additionally, it covers how to define shapes such as squares using vertices and edges, and outlines the OpenGL rendering pipeline including shader programs and drawing methods.

1. Introduction To
OpenGLES in Android

2. OpenGLES
●
Graphics Library for 3D

3. OpenGLES Terms
●
●
●
OpenGLES : Graphics API for doing 3D
operations on GPU / CPU
Primitives : lines, point, triangles
Texture : make the image
realistic by adding bitmap

4. CPU versus GPU
●
CPU
–
–
●
good at executing sequential code
Handles branches well
GPU
–
–
Same code, multiple data
Parallelism (ideal for image rendering)

5. 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

6. View
●
●
Manages the memory that can be composited
into the Android view system
Renders display in a separate thread,
decoupling from UI thread

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

8. Two Steps
GLSurfaceView
GLSurfaceView.Renderer

9. GLSurfaceView
GLSurfaceView view = new GLSurfaceView(this);
view.setEGLContextClientVersion(2);
view.setRenderer(new SquareRenderer());

10. 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

11. GLSurfaceView.Renderer
public class SquareRenderer implements GLSurfaceView.Renderer {
public void onSurfaceCreated(GL10 unused, EGLConfig config) {
GLES20.glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
}
public void onDrawFrame(GL10 unused) {
GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT |
GLES20.GL_DEPTH_BUFFER_BIT);
}
public void onSurfaceChanged(GL10 unused, int width, int height) {
GLES20.glViewport(0, 0, width, height);
}
}

12. Make sure to add this!

13. Drawing a Basic
Shape

14. 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.

15. -0.5f, -0.5f, 0.0f, // Bottom Left
0.5f, -0.5f, 0.0f, // Bottom Right
-0.5f, 0.5f, 0.0f, // Top Left
0.5f, 0.5f, 0.0f, // Top Right

16. 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);
}

17. Draw a square
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

18. GL_POINTS
GL_TRIANGLES
GL_LINES
GL_TRIANGLE_STRIP
GL_LINE_STRIP
GL_TRIANGLE_FAN

19. OpenGL Rendering Pipeline Simplified

20. 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

22. Vertex Shader
attribute vec4 vertexPosition;
void main(){
gl_Position = vertexPosition;
}
Fragment Shader
precision mediump float;
void main(){
gl_FragColor = vec4(0.5, 0.5, 0.5, 1.0);
}

23. Loading the Shader
int vertexShader =
GLES20.glCreateShader(GLES20.GL_VERTEX_SHADER);
GLES20.glShaderSource(vertexShader, shaderCode);
GLES20.glCompileShader(vertexShader);
• GLES20.GL_FRAGMENT_SHADER

24. Compiling and Linking the Shader
program
shaderProgram = GLES20.glCreateProgram();
GLES20.glAttachShader(shaderProgram, vertexShader);
GLES20.glAttachShader(shaderProgram,
fragmentShader);
GLES20.glLinkProgram(shaderProgram);

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

27. 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);