The game mentioned in the last post was completed! We demonstrated this game system in last week’s Build18 event from the ECE department (Project Haptic Rhythm Music Game). Here are some photos of the system:

The vibrating motors (the black discs in the photos) are fun! It provides a very powerful haptic effect as we attach it to a 5V power source and switched by a MOSFET from Raspberry PI GPIO ports.

And the code is structured so that it’s very easy to create customized games! You only need to create a “note” file containing the starting/ending timestamp and channel (1-4) for each block, and point the global constants in state.c to the new mp3 and note file.

tyz is currently developing a game based on OpenGL ES 3.0 for 3D graphics. This article will review how to develop an OpenGL ES 3 application.

Shaders

There are two types of shaders: vertex shader and fragment shader. Vertex shader processes data for each vertex and both specifies the actual position in the “clip space” (gl_Position) and passes data to fragment shader. Based on the incoming data, fragment shader processes data for each fragment (similar to pixel, so fragment shaders are sometimes called pixel shaders) and specifies the color for the fragment. Both of shaders run on GPU to reduce CPU processing load.

This statement actually has a issue. Suppose you want to draw a triangle and the vertex shader passes on data about the three vertices. However, there are much more than three fragments inside the triangle surface that expects input. The graphics hardware will actually perform interpolation on the data from the output of vertex shader to input of fragment shader. Users can specify “flat interpolation” in OpenGL ES 3 API to disable such interpolation.

As users can write custom shaders, OpenGL ES 3 does not use a fixed graphics pipeline to perform different operations, like OpenGL ES 1.x. To support things like lighting effects, users should write vertex and fragment shaders.

Attributes and uniforms

Input data are passed to the shader programs through attributes and uniforms. Attributes can be different for different input vertices. You can input either an array or a single element and the corresponding data for each vertex will go to shader input. However, OpenGL ES 3 requires a minimum of 16 attributes for all implementations, so to make program runs on every platforms that conforms to OpenGL ES 3 specification, the user can use at most 16 attributes. Uniforms are the same for all vertices, and the minimum number of supporting uniforms are much larger.

Vertex Buffer Objects (VBO) and Vertex Array Objects (VAO)

Data transferring between main memory and graphics memory are expensive. It is not very efficient to transfer memory on each draw operation. OpenGL ES 3 supports creating a buffer on the graphics memory and storing data there, so that drawing is more efficient. Users can create a buffer by glGenBuffers and store by glBufferData. This is known as Vertex Buffer Objects. Because there are fixed number of buffer targets, users can use Vertex Array Objects to store multiple vertex array data, vertex indices data, etc. in different places.

Textures

Textures can be applied when drawing objects. You can create a texture by glGenTextures and input the bitmap data into the texture by glTexImage2D. Then you can access texture data in shader programs by a sampler2D uniform.