Question

I’m currently exploring opengl through the use of the JOGL library (the java wrappers for openGL) which I’m using to create 2d/3d graphs. At the minute I’m having a little issue with text I’ve rendered through the “glutBitmapString” method, it isn’t resizing in respect of the window as shown in the screenshot below. Unfortunately the job spec I’ve been given is that this must be done in Java, so I can’t jump to any other language that has a better supported version of openGL.

Everything else in the window resizes correctly so I’m assuming the issue is in the code I’ve posted below, if not then I’ll be happy to post code you feel is relevant to the issue.

Here is a snippet of my code I’m using to render the text

GL gl = drawable.getGL();
    GLUT glut = new GLUT();

    float textPosx = -0.4f;
    float textPosy = -2.1f;

    gl.glColor3f(1.0f, 0.0f, 0.0f);

    // Move to rastering position
    gl.glRasterPos2f(textPosx, textPosy);

    // convert text to bitmap and tell what string to put
    glut.glutBitmapString(GLUT.BITMAP_HELVETICA_12, "0");

    textPosx = 1.75f;
    textPosy = -2.15f;

    // Move to rastering position
    gl.glRasterPos2f(textPosx, textPosy);

    // convert text to bitmap and tell what string to put
    glut.glutBitmapString(GLUT.BITMAP_HELVETICA_18, "TIME");

    textPosx = -1.0f;
    textPosy = 1.0f;

    gl.glColor3f(0.0f, 1.0f, 0.0f);

    // Move to rastering position
    gl.glRasterPos2f(textPosx, textPosy);

    // convert text to bitmap and tell what string to put
    glut.glutBitmapString(GLUT.BITMAP_HELVETICA_18, "ERRORS");

Answer 1

glutBitmapString draws text in 2D. 2D text size is based on font size. So, if you set the font size to 18, as you have in this example, then it will be standard 18 pt font size on the screen, no matter how large you make the window or how close you zoom in. This is not a Java issue. Java is not actually drawing anything. Everything is being drawn by the OpenGL native libraries, which are written in C++, so it will be exactly the same in C++ as it is in Java.

There are two ways you could work around this. One would be to change the font size of the text as you zoom in or out. This would be kind of a awkward, and may be difficult to get right. A better option, imo, would be to simply use 3D text. In JOGL you use the TextRenderer object to draw 3D text.

In your init method create a global variable like so:

textr = new TextRenderer(new Font("SansSerif", Font.PLAIN, 18));

Obviously, change the font settings to whatever you prefer. Then in your display loop:

textr.setColor(Color.GREEN);
textr.begin3DRendering();
textr.draw3D("ERRORS", xLocation, yLocation, zLocation, scale);
textr.end3DRendering();

Personally, I prefer to use a large font size and then scale it down some, that way, when you zoom in, it doesn’t get pixelated.

Also, unlike 2D text, 3D text will not always face the screen. You have to do that manually. It depends on how your camera is set up, but if you’re using basic rotations to move the camera around, usually you can just negate those rotations on the 3D text object to make it face the camera.

For the x, y, and z locations, those are the locations within the current object (local coordinates). Think of the beginRendering() to endRendering() as one object with its own local coordinate system. Usually, I prefer to draw my text at 0, 0, 0 local coordinates, then move the entire object to the proper location. That way rotations are easier to understand.