Hi.
I'm trying to draw a rotating square with shaded colors (red one side with a gradient to yellow on the other side).
There are some artifacts in P2D as you can see in this snippet (I'm using Processing 1.5.1):

1. void setup() {
2.   size(400,400,P2D);
3.   smooth();
4.   frameRate(30);
5. }
6. void draw() {
7.   background(0);
8.  
9.   translate(200,200);
10.   rotate(radians(frameCount));
11.  
12.   beginShape();
13.   fill(#ff0000, 50);
14.   vertex(-100,-100);
15.   vertex(+100,-100);
16.   fill(#ffff00, 50);
17.   vertex(+100,+100);
18.   vertex(-100,+100);
19.   endShape(CLOSE);
20. }

Artifacts are visible only when the red side is positioned right/bottom.They disappear when not smoothed.
Any hint to remove them?
Here is an example of what I mean:

There is a number of (mostly) white points where single shaded rectangles are oriented left/north. Artifacts are always on side right/bottom and if the background is pitch dark they are more visible.

I also saw that this shading is not available in JAVA2D (it is rendered as a single color). Is this true or am I missing something?

OPENGL would work (instead of P2D) but here I found another issue I cannot solve.
I create a background OPENGL image (PGraphics) where I draw. This image is far bigger than the screen and I prefere to copy it to the smaller screen only when elaboration is complete.
Doing so I use

1.  copy(img, 0,0,img.width,img.height, 0,0,width,height);

and I get an error message:

Exception in thread "Animation Thread" java.lang.IllegalArgumentException: Illegally formatted version identifier: "null"

Any idea?

Thank you in advance for any help in solving the issue.
Alessandro