iOS-使用OpenGL ES 2.0显示文本

Question

I'm surprisingly struggling a lot to display text with OpenGL ES 2.0. There are a ton of posts on stackoverflow, debating the subject, showing a few lines of code, or showing links from 2010 but working with OpenGL ES 1.x (not compatible).

But they are quite vague, and to my knowledge there is not complete code or convenient way to display text with version 2.

Do you know if there is a modern way to display text ? Like just adding a pod and writing something like this ?

[font drawText:@"This is a text" size:@12];

Thanks a lot in advance, any help would be very much liked.

EDIT 1 : I have to use OpenGL 2.0, and I can't use something else, for internal reasons.

EDIT 2 : I've found two libraries that do it :

• FTGLES : It crashes at runtime when I try to use it
• https://github.com/chandl34/public/tree/master/personal/c%2B%2B/Font

This one is simple but written for ES1, so I need to port the code to ES2.

EDIT 3 : ES1 and ES2 are different : ES2 works with shaders.

Answer 1

Since you are targeting ES2 and shaders are supported it might be a bit hard to create a tool that does this for you. But if you find such a tool it might be conflicted with your flow in many ways such as binding its own shaders and buffers, using settings on blending, depth buffer... Then if it would do that you are having trouble as you may not have a good control over how and where the text is drawn (on a 3D rotating box for instance).

But from your question (it's snippet) it seems more like all you want to do is add some 2D overlay with text which would look exactly like using an UILabel . If this is the case then I suggest you to actually use UILabel to draw these texts. You can add all of these views easily on your view that shows openGL content.

In the other case where you still need to draw text on a 3D object and want to do it very easily I suggest you to still use UILabel but create its screenshot and push it to a new (or atlas) texture. Then you can draw it as any other object. UILabel will then handle all fonts, alignments, colors, multiline and text wrapping, font size adjustments... So if you already have a system to draw a texture in the scene you should not be too far from creating yourself a tool that draws some text on the screen since you use a texture to transfer the data.

Answer 2

Nothing has changed since OpenGL ES1. Usually text is displayed in planar projection and created quads that are textured using font texture. There are many tutorials on this topic. One example how to do it. However, this is quite a lot of work when you started from scratch.

There might be better way, but depending on what you plan to do might not be suitable. You may mix UIKit with OpenGL view, having text drawn with UIKit as overlay. (UILabel, UIButton..etc.)