Drawing Text to a canvas

OpenGL Development JOGL Development
#1

Hi, I am writing a jogl application and would like to display worlds and letters on the glcanvas. Can anybody tell me how I’d go about writing “hello world” (a really original example ;D )onto a glcanvas at specified co-ordinates ?

Tks

Sally

#2

Drawing text isn’t as easy as you might suspect. But the GLUT function glutBitmapString() in JOGL helps for simple text.

Here is a Hello world chunk you could safely inject into your display() method to get you started:

gl.glPushMatrix();
gl.glLoadIdentity();

gl.glMatrixMode(GL.GL_PROJECTION);
gl.glPushMatrix();
gl.glLoadIdentity();
gl.glDisable(GL.GL_LIGHTING);

gl.glColor3f(1.0f, 1.0f, 0f);
gl.glRasterPos2f(0f, .5f); // <-- position of text

glut.glutBitmapString(gl, GLUT.BITMAP_HELVETICA_12, "Hello World");

gl.glEnable(GL.GL_LIGHTING);
gl.glPopMatrix();
gl.glMatrixMode(GL.GL_MODELVIEW);
gl.glPopMatrix();
#3

Another related question :

Once I have a window (or a fullscreen) with a GLCanvas, is it possible to alternate phases where I use the GL display, and phases where I would use the canvas with standard AWT or swing display operations?
For example a game using 3D display, and when the match is finished I display a score table (but no more 3D at all).
Is that possible?

#4

Ive wondered if we could render text to offscreen BufferedImage using the Java2D methods.

Then somehow use inmemory BufferedImage and render to a screen.

  • dynamically bind to a model
  • render to 2D overlay canvas (if this is possible)

Is it possible to have 2D overlay layer on top of the glcanvas. It could display the textual information.

#5

Following on from that you can draw to a BufferedImage using Java2D and from that to a texture and then draw the texture.

#6

This whole discussion leads me to a question on performance with writing text.
What is faster (and why), bitmaps or textures?
In particular in regards to non-scaling text. i.e. text that ignores projection/distance/depth etc and always draws to the same number of pixels.

#7

Textures would be faster because the image is stored on card, and so can the vertices be if the text is static.

#8

Thank you for your help. However, with your original code the graphics failed to render after displaying the text. I stripped out some of the lines to leave it like this:

 
    gl.glColor3f(1.0f, 1.0f, 0f); 
    gl.glRasterPos2f(0f, .5f); // <-- position of text 
    glut.glutBitmapString(gl, GLUT.BITMAP_HELVETICA_12, "Hello World");

and then it seemed to work perfectly.

Just wondered what those other lines were about as it works without it. What am I missing here :stuck_out_tongue:

Txs

Sally :slight_smile: