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  Do I need the stencil buffer for this?  (Read 589 times)
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Offline conehead

Junior Newbie





« Posted 2013-08-23 16:32:00 »

Hey all!

First of all I'm really new to this scene. I know Java, but hardly know OpenGL / Game Development.
Today I spent a lot of time reading several tutorials about libgdx.

Now I wanted to create an effect that looks like this:

I got 2 players and a simple background image.
Now I want to use these players as alpha map for my background.
So the players could move, but the background does not move.
Like an "inverted" world.

Do I have to use the stencil buffer for this?
Or may be there better options?
Is it just a simple (combined) alpha map?

Hope you can help me!
Thanks!
Offline RobinB

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Medals: 44
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« Reply #1 - Posted 2013-08-23 17:46:22 »

Maybe an frame buffer.

- Bind buffer
- Draw characters
- Unbind Buffer

- Bind shader
- Draw Texture
- Unbind shader
Offline Zhon

Junior Member


Medals: 4



« Reply #2 - Posted 2013-08-23 18:00:50 »

Give this a try:
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*draw background*
GL14.glBlendFuncSeparate(GL_ZERO, GL_ONE, GL_SRC_COLOR, GL_ZERO);
*draw both these fighters*
GL11.glBlendFunc(GL_DST_ALPHA, GL_ONE_MINUS_DST_ALPHA);
*draw a white quad surrounding both these fighters*

Hope it works.
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Offline conehead

Junior Newbie





« Reply #3 - Posted 2013-08-24 13:39:40 »

Thanks RobinB, I will take a closer look at the FrameBuffer.

And as soon as I add this line:
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Gdx.gl20.glBlendFuncSeparate(GL20.GL_ZERO, GL20.GL_ONE, GL20.GL_SRC_COLOR, GL20.GL_ZERO);

I get a NullpointerException.

Any ideas? :/
Offline davedes
« Reply #4 - Posted 2013-08-24 15:41:01 »

You need to enable GL20 to use Gdx.gl20.

http://badlogicgames.com/forum/viewtopic.php?p=42087#p42087

Online Riven
« League of Dukes »

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Projects: 4
Exp: 16 years


Hand over your head.


« Reply #5 - Posted 2013-08-24 16:29:00 »

Just render white pixels if they are not fully translucent in the texture sample.

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