Rendering Text in OpenGL 2.0 ES on Android

Hello all,

I have just finished porting fractious’s Rendering Text in OpenGL on Android to OpenGL ES 2.0 (this is the mobile version of OpenGL 3.0 and the main difference with the older versions OpenGL is having acces to the shaders, which allow us to run code on the GPU).

I had to do this because my project TheHunt uses, you guessed it, the newer version. Reason is that it would allow me to do some nifty shader tricks… some day 🙂

So here is my code – https://github.com/d3kod/Texample2. Feel free to use it for whatever you want as it is licensed under the CC0 1.0 public domain license.

Texample2

The example application, Texample2

Some implementation details:

  • I firstly started by simply converting the OpenGL ES 1 commands to the newer version. The Model, View and Projection matrices were passed using a uniform variable to the shaders, i.e. all the letters used the same matrices. This was good enough to produce horizontal text
  • In TheHunt I use text to label events (fishbone flops, net snatches), and I need this text to be tilted (it would be somewhat boring otherwise). For this I needed to be able to assign individual model matrices to each word. A bit tricky, but using Sprite Batching in OpenGL ES 2.0 | Anton Holmquist as inspiration I managed to do it. In short, instead of an uniform Model-View-Projection matrix, the vertex shader has an uniform array of matrices. I fill this array with an individual matrix for each letter and also pass a matrix index attribute for each vertex (the exact same method suggested by Anton Holmquist.) The result is that each GLText::draw call can tilt the string drawn with a certain angle (it can now receive an angle argument, in degrees).
  • The last catch was drawing color text – at first, all text was coming out black for me. The reason turns out to be that the texture is defined as grayscale, so in the fragment shader we need to multiply the color we want for the text (passed as uniform u_Color) with the grayscale value (called W in OpenGL) of the texture (not with the whole texture color, because it is something like [0, 0, 0, grayscale] which was resulting in the all black text):

gl_FragColor = texture2D(u_Texture, v_TexCoordinate).w * u_Color

— from BatchTextProgram.java

That’s all I can think of, and the result is efficient text drawing in OpenGL ES 2.0, and more importantly in TheHunt, where you can expect a nice GUI to appear soon!

TheHunt – Interactive graphical platform for AI experiments

Hello!

Firstly, I apologize for the rather big break – I will try to be more regular from now on…

But finally I feel like I have something noteworthy to say, and show:

TheHunt

Prey casually flopping around

Prey casually flopping around

http://d3kod.github.com/TheHunt—Interactive-graphical-platform-for-AI-Experiments/

On the website above you can:

  • Download the current best version
  • View the full source code
  • Contribute! bug report, bug fix, adding a feature… or just a friendly comment on it, all are priceless =]

Short story:

  • Android game and live wallpaper simulating an artificial environment with algae and a fish (currently more like a fish bone, really)
  • Fish tries to eat as much as it can, munching on algae and food you’ve placed
  • You can catch the fish by surrounding it with a net
  • Open sourced, idea is to end up with other agents using the environment, maybe even interacting with each other (a crab? a seal?…)
  • Will be in the Play Store, eventually, when it matures enough

I will be using this blog to post regular updates on it, as well some behind the scenes information about how things work… also to answer to feedback you guys might have!

That’s it for now, I’ll be back soon to tell a bit more about some incoming features and maybe set some milestones!

More screenshots:

Prey hiding under algae, having heard the nearby net

Prey hiding under algae, having heard the nearby net

 

Catching the prey in the net!

Catching the prey in the net!