Arvind Devraj's overview of OpenGL and RenderScript

1. High Performance
Graphics and Compute
OpenGLES and RenderScript
Arvind Devaraj

2. Agenda
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Introduction : Graphics terms
●
Graphics on GPU
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OpenGL Android Graphics
●
Graphics Pipeline
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Shaders
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High Performance Compute on GPU
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RenderScript

3. Graphics Terms
●
●
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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
–
Same code, multiple data
GPU
–
Parallelism (ideal for image rendering)

5. Graphics on GPU

6. Graphics Pipeline

7. OpenGLES Android Graphics
●
Graphics Library for 3D

8. Android Graphics Classes
GLSurfaceView
GLSurfaceView.Renderer
View
➢
- connects SurfaceView to OpenGLES library
Renderer - responsible for making OpenGL calls to render a frame
➢

9. GLSurfaceView
GLSurfaceView view = new GLSurfaceView(this);
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) {
Code when surface is created
}
public void onDrawFrame(GL10 unused) {
Code for drawing the frame ( Square )
}
public void onSurfaceChanged(GL10 unused, int width, int height) {
When surface is changed (rotated etc)
}
}

12. Drawing a Square
draw() {
float coords[] = { .... };
vertex 'buffer' created with the coords
glVertexPointer(buffer) :
}
glDrawArrays(TRIANGLE_STRIP ...);
,

13. Drawing a Square
draw() {
float squareCoords[] = { .... };
ByteBuffer vbb = ....
squareVB = vbb.asFloatBuffer();
squareVB.put(squareCoords);
gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);
}
gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP 0, vertices.length / 3);
,
Full code:
https://github.com/arvind-devaraj/androidopengles/blob/master/3_SquareRenderer/src/com/example/graphics1/Square.java

14. OpenGL Rendering Pipeline

15. Shaders
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Shaders are programs that execute on the GPU
●
Shader programs operate on
–
Each vertex
–
Each pixel

16. Shader Programs
• Vertex Shader – operates on each vertex
• Fragment Shader – operates on each pixel
• Shaders are compiled and linked ( like any program )
• Executable is sent to the GPU

18. 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);
}

20. CPU – GPU communication

21. GPU for General Programs
●
Graphics is accelerated by the GPU
●
Can GPU accelerate other programs ?
–
●
e.g. Matrix multiply, encryption
OpenCL, CUDA, Renderscript are API
–
used for general purpose GPU

22. RenderScript
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A high level API to access GPU
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Provides high performance Compute
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Provides uniform API across multiple SoC
●
Alternative is NDK (but NDK is platform
specific)

23. RenderScript – Use cases
●
What functions can be accelerated
–
Graphics
–
Image Processing
–
Encryption
–
Signal processing
–
Mathematical functions

24. RenderScript - Flow

25. RenderScript – CPU side
Class Hello extends Activity {
Allocation input;
Allocation output;
RenderScript rs = new RenderScript()
ScriptC_func script = new ScriptC_func(...)
}
script.forEach_root(input, output)

26. RenderScript – GPU side
Hello.rs
void root (char *in , char *out) {
*out = *in * 2
}

27. RenderScript
●
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Advantages : Compared to NDK, provides an easy device
agnostic way to accelerate performance on GPU
Disadvantages : C99 standard, debugging is restricted

28. Renderscipt - Summary
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Renderscript is an API to access GPU
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Used for High Performance
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High Performance Compute / Graphics
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Compute, Math , FFT, convolution, Signal processing
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Support Graphics – but not a replacement for OpenGL
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Works on all GPUs ( if supported by SoC ) otherwise on CPU
●
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