The following sketch draws a series of points. When I change the alpha value for stroke() to anything less than 255 [line 11], the points draw on only the left ~1/3 of the sketch. I do not understand how changing the alpha could cause this to happen. I have tested this in 1.2.1 and 1.5.1 with the same results.

1. float a = -0.966918;
2. float b = 2.879879;
3. float c = 0.765145;
4. float d = 0.744728;
5. float x = 0.1;
6. float y = 0.1;
7. 
   
8. void setup() {
9.   size(400, 400);
10.   background(255);
11.   stroke(0,255); // this is the line in question
12. }
13. 
    
14. void draw() {
15.   translate(200, 200);
16.   float xNew = sin(y*b) + c * (sin(x*b));
17.   float yNew = sin(x*a) + d * (sin(y*a));
18.   x = xNew; y = yNew;
19.   point(x*100, y*100);
20. }