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Ond?ej Byrtus

OpenGL How to clearly highlight GUI object regardless of its color

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I am working on GUI for my game, but I think this question could apply to any object in general - How to clearly highlight object regardless of its color? Currently I am blending its result color with other semi-transparent color(light blue), but obviously - this does not work for blue objects.

 

What are my options if I would like an object highlighted? I am looking for OpenGL shader solutions, best in customizable ones (e.g. more variants/ intensities).

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There is a trick in, I think, one of the Graphics Gems books: drawing an high-contrast overlay on any background by flipping the most significant bit of each colour component of the current frame buffer colour. (Yes, it could be done in OpenGL.1.0/2.0 without shaders.) Increasing or decreasing each colour component by half the maximum value provides more than enough contrast with adjacent unaltered pixels.

 

This technique might look bad with unpleasant frontiers between high and low values (slightly noisy backgrounds with components around half amplitude explode into spotted patterns) or simply because the overlay echoes the same texture as the background.

 

If you can afford to prepare graphics more carefully you might simply draw something normally, fully opaque, with a double outline: one dark and one light. The contrasting outlines can't both be confused with the background, and they form a high-contrast edge between them. A double outline can often be simplified to a dark outline with a light fill or vice versa, particularly in the case of text in solid colours.

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An interesting way - I would not thought of that. smile.png

 

However, I probably misled you in my original post. I am dont technically need to be in contrast with background(game) - the button's color/texture I will choose manually. My thoughts were, if I once go through all the GUI implementing, I will probably use it in my next game too. But that also mean, the button can be of other color/texture in the next game and I would like to have some nice MouseOver effect on it - regardless of its color.

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Do you really need an automatic approach? I would think that having different "themes" for each UI would be the best approach. In my UI library, I have implemented the possibility of parsing UI themes from a XAML-like file. This way you can specify all the UI appearance without needing to recompile everything. You can have a look at this post in my journal.

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Well, technically I dont. And the more I think about it, the more I realize I probably dont need it. I just wanted to have some default GUI style for quick prototyping that would work OK anywhere.

It is interesting - this is exactly what I am trying to achieve with OpenGL. Reinventing the wheel and creating cross-platform XAML based GUI for my games. Actually I think there is no good free GUI for OpenGL games (Yes, I know there is CEGUI, but I tried it and I did not like it - I dont think I really need 1500+ classes for GUI) at all.

Edited by Ond?ej Byrtus

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I assume you are using C++ otherwise I'd be open to the idea of making it cross-platform. But at the moment I only have the time to continue its SharpDX/D2D development. Feel free to have a look anyway, the code is freely available on github.

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If we're talking about buttons and such, one possibility would be to use greyscale for disabled, desaturated for normal, and fully saturated colour for highlighted. This will always work irrespective of the current background.

Edited by mark ds

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The grayscale for disabled is great, but I would like to stick with "normal" for normal. Is there some kind of vivid manipulation?
@wodinoneeye can you link some example of result? It is quite hard to imagine how it looks like.

 

The most obvious solution would be some kind of light "blur behind" similar to Windows Aero title bars. Link

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I would outline the object with another color. If you've ever seen a movie with closed captions or subtitles, you would likely find it difficult to read the words if the background color is similar to the font color. The remedy for this was to outline the text with another color (doesn't matter what). That way, the words are clearly visible regardless of the background.

 

In terms of selection highlights, you can do that in several ways (to draw attention to the selected button). You could do a button pressed graphic (literally, makes the button look pressed in), you could make the button slide out when the mouse is over it (for instance, 32 pixels to the right if the interface is along the left side of the screen), you could change the alpha (make it transparent, or more transparent if it's already transparent), you could make a shuriken fly into the button that's selected, etc.

 

Are you making an engine? A lot of people are concerned about reusing their code in several projects. I understand not wanting to reinvent the wheel, but you also don't want to be too repetitive with your design, even if you're developing a series of similar titles. Take the Naruto: Ultimate Ninja series for instance. The design is slightly different each time (I was unable to find a screenshot of the third PS2 title). These games also utilize outlines for selection, and also animation once pressed.

 

529520-shonen-jump-naruto-ultimate-ninja480303-shonen-jump-naruto-ultimate-ninja

 

Please forgive me if I misunderstood your question. I hope I could help somewhat!

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You could do a button pressed graphic (literally, makes the button look pressed in

That effect sounds cool, any ideas how is it done?

 

 

Here is an easy way to make buttons::

 

Button_Tutorial.png

 

You can do this at any size you like, and also experiment with border sizes and blurring. Just choose a fill color or texture. For specialized buttons, I would recommend drawing them manually (Gimp is great, and a free alternative to Photoshop). But this can be used as a starting point if you don't currently have another method. Sorry for my late response!

Edited by Mia.

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