Processing 1.0 - Processing Discourse - weird rotate() problems

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Index › Programming Questions & Help › Syntax Questions › weird rotate() problems - snippet inside

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weird rotate() problems - snippet inside (Read 1192 times)

zpousman

weird rotate() problems - snippet inside
Sep 25^th, 2005, 1:17am

I'm having some trouble rotating shapes (rects).

I can't seem to find the origin of rotation. When I rotate a shape a few different times (putting the rotation back each time), like 0, 15, 30, 45 -- the rectangles "slide" to the left (i.e, negative x) and the bottom (i.e., positive y).

Do I need to reposition my object at (0,0), rotate it there, and reposition it?

Or is there something else I should try?

<blockquote>
void bigRect(int x, int y, int lineSize, color col, float rot) {
// x, y, of center. lineSize is 1, 2, 3. col is color. rot is rotation - degrees.
int sizer = lineSize*lineSize*25;
fill(col);
if (rot == 0) //rotation is 0
{
rect(x, y, 300, 5);
}
else {
rotate(radians(rot));
fill(black);
rect(x, y, 300, 2);
rotate(-radians(rot)); //reverse the rotation so that we can go back to 0,0 for remaining shapes
fill(dkblue);
rect(x, y, 300, 3);
</blockquote>

seltar

Re: weird rotate() problems - snippet inside
Reply #1 - Sep 25^th, 2005, 2:32am

guess you're looking for something like this:

Code:


  void bigRect(int x, int y, int lineSize, color col, float rot) {
  // x, y, of center. lineSize is 1, 2, 3. col is color. rot is rotation - degrees.
  int sizer = lineSize*lineSize*25;
  fill(col);
  if (rot == 0) //rotation is 0
  {
    rect(x, y, 300, 5);
  }
  else {
    pushMatrix();
    translate(x,y);
    rotate(radians(rot));
    translate(-x,-y);
    fill(black);
    rect(x, y, 300, 2);
    rotate(-radians(rot)); //reverse the rotation so that we can go back to 0,0 for remaining shapes
    fill(dkblue);
    rect(x, y, 300, 3); 
    popMatrix();
  }
}

-seltar

I'm bored, therefore I program
http://seltar.org > seltar's special place
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zpousman YaBB Newbies Offline Posts: 7 GA	Re: weird rotate() problems - Solved! Thanks. Reply #2 - Sep 25^th, 2005, 6:31pm Seltar's solution works like a charm. I knew there was somthing that I wasn't doing, but I couldn't figure out how to use pushMatrix( ) and popMatrix( ). Thanks.

error

Re: weird rotate() problems - snippet inside
Reply #3 - Jul 1^st, 2007, 12:05am

Hi,

I guess I'm having a similar problem with the rotate() function. I have this:

void setup()
{
frameRate(30);
size(1024, 400,OPENGL);
smooth();
}
void draw()
{
int num = 4;
background(0);

for(int i = 0; i < num; i++)
{
noStroke();

//171 and 163 are just random numbers
curve(171, 163 ,0, width/2, height/2, 0, random(0,width/4), random(0,height/4), 0, 171, 163,0);

}
}

I want to be able to rotate this, taking the centre point (width/2,height/2) as the origin. I read somewhere that I need to mark the first point of the curve to 0,0 (rather then (width/2,height/2) and then translate the whole thing to the centre point because the default origin for rotation in processing is 0,0. But i couldn't make it work and I can not understand what pushMatrix() and popMatrix() are meant to do.

any help would be great,

thanks,

e.

Re: weird rotate() problems - snippet inside
Reply #4 - Jul 4^th, 2007, 6:33pm

pushMatrix() saves the current matrix to the stack
popMatrix() restores last stack entry

why use it? so we dont have accumulative transformations when we dont need them.. (they are also useful, yes)

//currently we are at the origin (0,0,0)
pushMatrix();
translate( 10, 10, 0 );
drawObject1(); // object is rendered at (10,10,0)
translate( 10, 0, 0 );
drawObject2(); // object is rendered at (20,10,0)
popMatrix();

drawObject3(); // object is rendered at (0,0,0)

in case you didnt saved the matrix before the translations and restored it later you would be rendering object 3 at position of object 2, (20,10,0)

i hope this helps you out.

Victor Martins | www.pixelnerve.com/v

TM Full Member Offline Posts: 133	Re: weird rotate() problems - snippet inside Reply #5 - Jul 24^th, 2007, 11:47am Hell yeah!! Thanks for that short but clear explanation!!!! Cheers
	))<>(( www.f u c k-dance-lets-art.com

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