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Index › Programming Questions & Help › OpenGL and 3D Libraries › PGraphicsOpenGL save() transparent background
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PGraphicsOpenGL save() transparent background? (Read 2002 times)
num3ric
PGraphicsOpenGL save() transparent background?
Oct 10th, 2009, 7:23pm  
Is it possible using PGraphicsOpenGL to save .png images with a transparent background?

I know it can be done using the normal PGraphics, but when it comes to OpenGL...

Thanks,
Eric
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ben_hem
Re: PGraphicsOpenGL save() transparent background?
Reply #1 - Oct 10th, 2009, 7:39pm  
http://processing.org/discourse/yabb2/num_1194820706.html#5

gabba gabba hey -- Ben
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num3ric
Re: PGraphicsOpenGL save() transparent background?
Reply #2 - Oct 10th, 2009, 7:58pm  
The example you're showing me uses the conventional PGraphics.

frameToSave.save("Output.png"); where frameToSave is a PGraphics.

I would like to know if the same code works for PGraphicsOpenGL.

For example, my code starts with:
Code:
import processing.opengl.*;
import javax.media.opengl.*;
import com.sun.opengl.util.texture.*;
import damkjer.ocd.*;


PGraphicsOpenGL pgl;
GL gl; 
Texture partTex;
Texture flashTex;


Can I make a transparent image with:
Code:
pgl.save("Output.png");
?

If not, is there a way to work around it?
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ben_hem
Re: PGraphicsOpenGL save() transparent background?
Reply #3 - Oct 10th, 2009, 8:11pm  
well, my workaround was to generate the graphics in an opengl window, and to copy the pixel[] array into a separate PGraphics object for saving.  If that doesn't work for you, maybe some more particulars would help?
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num3ric
Re: PGraphicsOpenGL save() transparent background?
Reply #4 - Oct 19th, 2009, 9:02pm  
Alright, I'm just going to answer to myself in order to close this thread.

After trying a few things, including your trick BenHem from which I obtained non-transparent renders in tones of blue, I concluded that it's not realistically possible. OPENGL and transparent backgrounds don't get along very well, just google it.

Plus, there was always a blue line in the middle of the images. The blue is probably related to this : "Strictly speaking the "blue" value from the source image is used as the alpha color." (Found in the dev section about PGraphicsOpenGL).

In conclusion, since I only wanted to add an animation layer on a video sequence, it was MUCH simpler to use a black background and apply additive mode in Final Cut.
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polymonkey
Re: PGraphicsOpenGL save() transparent background?
Reply #5 - Oct 19th, 2009, 10:45pm  
This might not be helpful but I got around this by rendering the scene again on a black background with all fill turned to white. This dumped out an alpha frame for each RGB frame. Any RGBA textures were rendered as just the alpha channel.

Worked like a charm in the end. But it does take twice as long to output.
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MattD(polymonkey)
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