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Topic: rotating a polygon (Read 559 times) |
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kevinP
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rotating a polygon
« on: Jan 20th, 2004, 1:03pm » |
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Hi,
I tried the first homework assignment in the course notes posted here by baffo. I came up with this:
Code:
float angle = TWO_PI/3; // angle (120 deg.) in radians
// tangent of an angle: ratio of the sine and cosine
float tangent = tan(angle);
int x = radius/2;
// intersects vertex
line(center, center, center+x, center+x*tangent);
// tangent to face
stroke(200,200, 50);
line(center, center, center, center+x*tangent);
stroke(0, 0, 255);
line(center + x, center + x*tangent, center + 2*x, center);
line(center + 2*x, center, center + x, center - x*tangent);
line(center + x, center - x*tangent, center - x, center - x*tangent);
line(center - x, center - x*tangent, center - 2*x, center);
line(center - 2*x, center, center - x, center + x*tangent);
line(center - x, center + x*tangent, center + x, center + x*tangent);
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How would I rotate this, say 15 degrees? So that I could specify the centerpoint, the radius of the circle that inscribes it, and an angle of rotation? Complete answer not needed, but a helpful hint is welcome.
Meanwhile I saw that I can simply this...
Code:
beginShape(POLYGON);
vertex(center+x, center+x*tangent);
vertex(center+2*x, center);
vertex(center+x, center-x*tangent);
vertex(center-x, center-x*tangent);
vertex(center-2*x, center);
vertex(center-x, center+x*tangent);
endShape();
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-K
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| « Last Edit: Jan 20th, 2004, 1:12pm by kevinP » |
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Kevin Pfeiffer
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kevinP
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Re: rotating a polygon
« Reply #2 on: Jan 27th, 2004, 10:40pm » |
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From the reference page for rotate():
"Positive numbers rotate objects in a counterclockwise direction."
But it seems to me that in my case this is working just the opposite...
Code:
translate(width/2, width/2);
rotate(2 * PI * 0.25); //
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I expected that this would give me a 90 degree counterclockwise rotation, but it looks to me more like 90 degrees clockwise... ?
-K
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Kevin Pfeiffer
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benelek
 
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Re: rotating a polygon
« Reply #3 on: Jan 27th, 2004, 11:51pm » |
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umm, the number 2*PI*0.25 gives half-PI radians, or (positive) 90 degrees. so the rotation occurs 90 degrees in the positive direction, which is clockwise in Processing. If you want to rotate the same amount counter-clockwise, use rotate( -0.5*PI ).
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kevinP
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Re: rotating a polygon
« Reply #4 on: Jan 29th, 2004, 11:59pm » |
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Hi benelek,
on Jan 27th, 2004, 11:51pm, benelek wrote:| umm, the number 2*PI*0.25 gives half-PI radians, or (positive) 90 degrees. so the rotation occurs 90 degrees in the positive direction, which is clockwise in Processing. If you want to rotate the same amount counter-clockwise, use rotate( -0.5*PI ). |
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So is the Processing reference wrong, or did (do) I misunderstand it
-K
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Kevin Pfeiffer
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REAS
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Re: rotating a polygon
« Reply #5 on: Jan 30th, 2004, 1:55am » |
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well...
the reference is incorrect. imagine that.
i'll fix it up.
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K Pfeiffer
Guest
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Re: rotating a polygon
« Reply #6 on: Jan 30th, 2004, 9:44am » |
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You've got a tough audience here. 
(But seriously, I just wanted to make sure that there wasn't some subtle point I had not caught).
-K
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REAS
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Re: rotating a polygon
« Reply #7 on: Jan 30th, 2004, 11:49am » |
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it's amazing, actually. that reference has been up for over a year and this is the first i've heard the problem. anyway, it's fixed now...
+ casey
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