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Index › Programming Questions & Help › OpenGL and 3D Libraries › Efficient way to draw large gradient
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Efficient way to draw large gradient? (Read 3032 times)
nigel_spleen
Efficient way to draw large gradient?
Mar 21st, 2007, 2:00pm  
Hello,

I'd like to use a gradient background for my sketch using Processing/OpenGL. The sketch can be large, 1000x1000 or so.  The gradient is 1-dimensional; i.e. the color changes along the vertical axis but not along the horizontal axis.  I'm very familiar with Java2D programming but not with Processing or OpenGL.

One possible solution is to render a 1-pixel-wide image and use that as a texture.  The image would need to be re-rendered when the sketch is resized so that the gradient is the correct height.

Specifically, I'm wondering:

- Is there a more efficient way to do this?

- If the dynamically-rendered texture image is the way to go, exactly how do I do this in Processing (i.e. how to render into a PImage)?

Thanks in advance for any tips!
Chris
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scloopy
Re: Efficient way to draw large gradient?
Reply #1 - Mar 21st, 2007, 6:44pm  
In GL, the solution would be to draw a QUAD and color the vertices. Here's some example code.

Code:
beginShape(QUADS);
fill(255,255,0);
vertex(0,0);
vertex(width,0);
fill(0,0,255);
vertex(width,height);
vertex(0,height);
endShape();

That will create a vertical gradient from yellow to blue. Just adjust the verts to suit your needs.

ryan
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« Last Edit: Mar 26th, 2007, 9:58am by scloopy »  
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nigel_spleen
Re: Efficient way to draw large gradient?
Reply #2 - Mar 21st, 2007, 8:48pm  
Thanks, that works great.  I knew about filling in vertices in this way, but for some reason I had assumed that it wouldn't work efficiently.  Go, hardware acceleration.

A minor correction, just in case anyone else reads this: The second and third lines should be "fill(255,255,0); vertex(0,0);".

Thanks again,
Chris
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scloopy
Re: Efficient way to draw large gradient?
Reply #3 - Mar 26th, 2007, 9:58am  
haha oops Tongue i fixed it
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movax
Re: Efficient way to draw large gradient?
Reply #4 - Apr 3rd, 2007, 12:31am  
But the quad will be just like any other 3D object, so you have to clear the depth buffer or far-away objects will be obscured by your background..
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« Last Edit: Apr 5th, 2007, 9:59pm by movax »  
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Simon G
Re: Efficient way to draw large gradient?
Reply #5 - Apr 23rd, 2007, 1:24am  
you can use a sphere to do more complex gradients too.
just put a big sphere and "spot-light" it with the color you want.
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