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Question about lesson 13


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#1 Sonic-blue-knight   Members   -  Reputation: 122

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Posted 23 February 2009 - 08:24 AM

hey there!, well, I'm not English but I try to understand everything in the tutorials. My question is... Why when I put the text further than x=-0.5 (for example at -0.6) the text dissappears?. Does OpenGL disable it for any special reason or something? Thanks in advance

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#2 Caste   Moderators   -  Reputation: 969

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Posted 23 February 2009 - 08:23 PM

As Jeff explained in his lesson, this depends on the projection (camera) setup:
Quote:
Now for a new command. glRasterPos2f(x,y) will position the Bitmapped Font on the screen. The center of the screen is still 0,0. Notice there's no Z position. Bitmap Fonts only use the X axis (left/right) and Y axis (up/down). Because we translate one unit into the screen, the far left is -0.5, and the far right is +0.5. You'll notice that I move 0.45 pixels to the left on the X axis. This moves the text into the center of the screen. Otherwise it would be more to the right of the screen because it would be drawn from the center to the right.


You can imagine your text being drawn one unit away from the camera, but as it does have a resticted view angle (meaning the angle between which it can see & record things), there's only a part of your scene visible. If you want to have text rendered at raster pos 0.5,0.5, then move your camera one step further away (glTranslatef(0.0f, 0.0f, -2.0f)) and you will see things again. But for simplicity stay in between [-0.5;0.5] for x and [-0.4;0.4] for y, this should be pretty much the whole screen.

#3 Sonic-blue-knight   Members   -  Reputation: 122

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Posted 23 February 2009 - 10:04 PM

Well I read that on the tutorial but guess I didn't understand everything.
So.. texts are really limited on the screen, aren't they?
If I wanted a text sliding horizontally on the top of the screen it would be really bad cause the text appears just on those regions, Am I right?
Changing the projection of the camera while testing a 3d world with the text it would affect the rest of visible objects too, wouldn't it?.

Thanks for your help.! ^^

Edit: Well, at least outline fonts can move freely around the screen without disppearing when the first character is out of the screen.

[Edited by - Sonic-blue-knight on February 24, 2009 4:04:32 AM]

#4 lc_overlord   Members   -  Reputation: 435

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Posted 24 February 2009 - 11:22 AM

Quote:
Original post by Sonic-blue-knight
Well I read that on the tutorial but guess I didn't understand everything.
So.. texts are really limited on the screen, aren't they?
If I wanted a text sliding horizontally on the top of the screen it would be really bad cause the text appears just on those regions, Am I right?
Changing the projection of the camera while testing a 3d world with the text it would affect the rest of visible objects too, wouldn't it?.

Thanks for your help.! ^^

Edit: Well, at least outline fonts can move freely around the screen without disppearing when the first character is out of the screen.


1. You should really use the method in lesson 17, it's much more reliable than lesson 13-15.

2. yea projection would change for the other objects as well, that's why you pop and push the matrices to reset the perspective.




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