Render text in foreground

Question

I am trying to render some strings in the foreground in a OpenGL/GLUT application under MacOSX 10.7.2.

At the moment I am using this code to draw a few lines in the foreground and it works fine.

void drawForeground() { int width = 10; int height = 10; glMatrixMode(GL_PROJECTION); glPushMatrix(); glLoadIdentity(); glOrtho(-1, width, -1, height, -1, 1); glMatrixMode(GL_MODELVIEW); glPushMatrix(); glLoadIdentity(); glDepthMask(GL_FALSE); glBegin(GL_LINES); //Draw the lines glEnd(); /*********************/ glPopMatrix(); glMatrixMode(GL_PROJECTION); glPopMatrix(); glDepthMask(GL_TRUE); }

Now I would like to draw also some text. In the previous function I added this piece of code in the line where I put the asterisks:

glRasterPos2d(2,2); glutBitmapCharacter(GLUT_BITMAP_HELVETICA_10, 'c');

but it didn't work. If I use the same two lines outside the drawForeground method the 'c' appears.
I already called glDisable(GL_TEXTURE_2D) and nothing changed.

May someone help me understanding my error?

Solution:

It turned out the solution to be disabling lighting using glDisable(GL_LIGHTING), reenabling it after rendering the text.

I would like to underline that the text is rendered always at the same dimension, independently from the parameters of the glOrtho call.

Your call to glOrtho() seems odd to me. Normally, I'd think you'd want it to be glOrtho(0, pixelWidth, 0, pixelHeight, -1, 1);. As it is, you're saying that your world is 11 x 11 units. It's possible that the letter is being drawn off the edge of the screen, depending on whether that (2,2) is where the baseline, ascenders or descenders go. — user1118321
– user1118321, Commented Feb 27, 2012 at 5:00
@user1118321 Thank you for your comment. I thought my call to glOrtho behave, in this case, as an implicit scaling. However, even changing it as you suggested (and using glRasterPos2d(width/2.0,height/2.0);) , I am still unable to see any letter. Even scaling it up and down seems to have no effect. — Manlio
– Manlio, Commented Feb 27, 2012 at 9:55
Yes, that is what glOrtho() does - implicit scaling. It just seemed odd to try to draw an 18 point character to an 11x11 area. Other than that, what you have looks reasonable. Are there any OpenGL errors along the way? — user1118321
– user1118321, Commented Feb 28, 2012 at 0:09
@user1118321 Well, actually you're right saying it's odd :) for the moment I changed it to a 10 point character. However, even if it may be too big I should equally be able to see something, at least a part of the char. There are neither OpenGL errors nor warnings... — Manlio
– Manlio, Commented Feb 28, 2012 at 16:27
I don't know if this is related, but according to this page, you need to disable GL_TEXTURE_2D to get the text to render. No idea why. — user1118321
– user1118321, Commented Feb 28, 2012 at 17:23

Solaraeus · Accepted Answer · 2012-03-04 07:55:48Z

Nothing certain, but a couple of things to try if you haven't already:

What is the color set to before you call glutBitmapCharacter()? If the drawing color is set to something that doesn't show up against the background, it could simply look like nothing is being drawn.

Have you tried calling glDisable(GL_TEXTURE) in addition to glDisable(GL_TEXTURE_2D)?

Are there other things like lighting that you enable anywhere else in your code, and then don't disable before rendering the text that might affect things? When I've run into bugs like this in the past, it seems like they are often related to something in the OpenGL state being in a state I didn't expect, often because I made some change to the state elsewhere and forgot to undo it. I would recommend that you try systematically commenting out various OpenGL calls in your code, even if they don't seem directly related, and see if the characters ever show up. If they do, then you'll know which state change you need to make/undo.

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