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Index › Programming Questions & Help › Syntax Questions › rotate and translate / understanding push pop
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rotate and translate / understanding push pop ? (Read 458 times)
vj_jess
rotate and translate / understanding push pop ?
Apr 13th, 2008, 10:56pm  
Hello !

I'm trying to get my head round the push pop method for placing stuff on screen. And it seems great for certain type of functions but I've run into a simple problem that you guys can help me with. I'm sure it will enable me to better understand this technique.

here's what I'm getting to :
http://farm3.static.flickr.com/2411/2410704467_9cbe7be48f_o.png

and this is the code :

size(300, 300);
randomSeed(4);
smooth();
background(255);
PFont tiza = loadFont("Tiza-90.vlw");
textAlign(CENTER);
translate(height/2, width/2);
textFont(tiza, 45);

float[] angle = {0, -PI/2, -PI/4};

for (int i = 0; i< 100; i++){
 fill(0);
 stroke(0);
 pushMatrix();

 rotate(angle[round(random(2))]);
 translate(random(-width, width), random(-width, width));
 scale(random(0.2, 1));
 text("black",0,0);
 popMatrix();
}
//save("test.png");



My problem is that I translate after the rotation. So its not simple to get words inside the canvas after a rotation.
My simple solution is this example is to increase the random translate out of the canvas size to be sure that all the canvas is filled with words. Is there a more elegant way to insure that after a  rotation a random translate stays in the canvas ?

Thx
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koogy
Re: rotate and translate / understanding push pop
Reply #1 - Apr 14th, 2008, 4:46pm  
a picture or description detailing what you're aiming for might be useful. 8)

that said, you have a screen of size width and translate by width / 2 so your coords go from -width / 2 to +width / 2

BUT you're choosing your random position from -width to +width which is twice the size of the screen...
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vj_jess
Re: rotate and translate / understanding push pop
Reply #2 - Apr 14th, 2008, 5:03pm  
The idea is simply to place text at a random position / scale / rotation on the screen. There's a link to the image in my first post.

And my question is how to translate and stay in the screen if you've already rotated ?
I use a random between -width and width to insure that I fill the screen with the text (even after a rotation !!) Its a cheap solution.
So how can I do this ?
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koogy
Re: rotate and translate / understanding push pop
Reply #3 - Apr 14th, 2008, 5:13pm  
> I use a random between -width and width to insure that I fill the screen with the text (even after a rotation !!)

but that means you're picking points outside the screen a lot of the time.

try

 translate(random(-width / 2, width / 2), random(-width / 2, width / 2));

and see the difference
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vj_jess
Re: rotate and translate / understanding push pop
Reply #4 - Apr 14th, 2008, 5:36pm  
Thx koogs that solves half the problem Smiley

It was actually another error in my code !

But this won't work as soon as I use a rectangular screen size (instead of a square). Once a text will have been rotated 90 degrees its X translate will end up representing a a translation on the Y axis of the screen.

So is there a simple math trick to link the right translation after a rotation ? Or a different way to do it ?

I'm used to code where you simply move the object!
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koogy
Re: rotate and translate / understanding push pop
Reply #5 - Apr 14th, 2008, 6:41pm  
> But this won't work as soon as I use a rectangular screen size (instead of a square).

well, you'll need to use height and width instead of width and width in the translation but it should be ok.

> My problem is that I translate after the rotation

not a problem

when you rotate, you are rotating the text around its centre* BEFORE doing the translate (try commenting out the translate like i mentioned last time and you'll see. try using different colours for each bit of text as well, stop you getting a black blob in the middle). then you are translating the rotated text to its new position, which is a case of choosing from -width/2 to width/2 and from -height/2 to height/2

try it, it'll take 5 seconds.

(* actually, you aren't, you are rotating around the middle of the baseline of the text. change the textAlign to (CENTER, CENTER) and that'll improve things)
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