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Render text in openGL

Started by gatofedorento Aug 12, 2012 at 1:49 PM 8 replies 3.1k views

Original Post

Aug 12, 2012 at 1:49 PM

Hey there.

I'm currently developing a GUI library from scratch, and after making the classes for buttons, windows, scrollbars etc I think its time to make them more user friendly by adding some text.

Today i tried to use the FTGL to draw some text, but the performance was very bad, just by drawing a window i got somewhat around 1300 fps, but if I drew it and a string ,with something like 20 characters, the framerate got around 200 fps using FTBitmapFont, it got even worse if I used FTPixmapFont.

I tried to use this library to avoid writting my own FreeType wrapper, basing myself on nehe's code that i saw here http://nehe.gamedev.net/tutorial/freetype_fonts_in_opengl/24001/ , though I think I could get a better performance from it.

Is there a better way to avoid these performance hits using FTGL?
Are there better text rendering APIs to use just to render some simple text on my GUI components? I don't really need anything complex, just some simple 2D text.

Cumpliments.

Waterlimon

Aug 12, 2012 at 1:54 PM

Does it drop even more if you draw lets say the screen full of text?

The cost of just drawing a window is so small that adding anything to it could multiply the time it takes to render a frame...

gatofedorento

Aug 12, 2012 at 2:13 PM

I will let you with two captions from my application, in the first one I have a window where I draw a button, one of my windows and a scroll bar, in the second one I draw the same components adding that "my text", and you can see the differences on the command line prompt in the left.

I think this was what you wanted me to show you...

http://i45.tinypic.com/2818owi.jpg
http://i50.tinypic.com/30ddt2p.jpg

Waterlimon

Aug 12, 2012 at 2:40 PM

No i meant does the fps drop more if you add more text.

like what happens if you display a string of lets say 100 characters?

and do you draw the string yourself or does the library do it for you?

gatofedorento

Aug 12, 2012 at 2:45 PM

With a string of somewhat 150 characters the framerate goes around 14 fps.

Its the library that draws it.

Waterlimon

Aug 12, 2012 at 2:54 PM

Random google search got me

"Getting rid of the "FaceSize" calls and using glScale instead resulted in a Framerate way above 100."

gatofedorento

Aug 12, 2012 at 3:11 PM

tried it and doesn't seem to change the font size, and if i don't even call "FaceSize" it doesn't even renders any text.

Thanks for help, maybe i need to dig a bit more the library, though, the tutorial isn't the best...

Waterlimon

Aug 12, 2012 at 6:15 PM

I believe the person who said that was calling it every frame or something. Try calling it once at the start...

Lazy Foo

Aug 12, 2012 at 9:53 PM

The way I created an OpenGL FreeType Font is by basically creating a bitmap font from the TTF font. I would take all the glyphs and render the bitmap for each glyph and then put them all on one texture.

Then I would treat this font texture like a sprite sheet and render a sequence character sprites to render lines of text.

This managed to get me pretty good performance.

gatofedorento

Aug 12, 2012 at 11:21 PM

That's what i intend to do, by doing that the only performance hit my application will take is creating the textures,
though that ain't a real problem because they will usually only be created on an init function

thanks for help, I will try that tomorrow.

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