Help! Why does this simple math return 0.0?

Android Processing

kodereakt..

Help! Why does this simple math return 0.0?

in Android Processing • 1 month ago

So I've struck upon a problem I can't fathom. I'm writing a sketch that draws to an off-screen OPENGL buffer and then resizes that buffer to display at the correct resolution.

Excerpt:

void setup() {

//doing stuff

appFrameBuffer = createGraphics(1280, 800, OPENGL);
dispWidth = appFrameBuffer.width * (height / appFrameBuffer.height);
}

void drawFrame() {

//drawing to buffer

imageMode(CENTER);
image(appFrameBuffer, width/2, height/2, dispWidth, height);
}

The variable dispWidth always gets filled with 0.0 even if I use real ints instead of vars.

Can anyone offer a suggestion?

Replies(7)

tfguy44

Re: Help! Why does this simple math return 0.0?

1 month ago

The value of "height" is undefined (and thus probably 0) until after your sketch's call to size().

Your sketch doesn't have a call to size().

Thus, the equation for your dispWidth variable is:

dispWidth = 1280 * (0 / 800); // This is 0.

Also, realize that 1/5=0, but 1/5.0=.2, and float(1/5)=.2 and 1/5f=.2

The difference there ius that the first is integer division, which results in an integer, and the rest aren't.

kodereakt..

Re: Help! Why does this simple math return 0.0?

1 month ago

Thanks tfguy! I do have a size call but I omitted it because I thought it was an obvious inclusion. (Maybe I'd be surprised?)

I.. think I understand what you said. :) I had a feeling maybe it was something like that. Numbers don't work good in my head. :)
If I understand, are you saying that I need to make everything either an int or a float?

kodereakt..

Re: Help! Why does this simple math return 0.0?

1 month ago

Indeed that was the answer.

dispWidth = float(appFrameBuffer.width) * (float(height) / float(appFrameBuffer.height));
image(appFrameBuffer, width/2, height/2, int(dispWidth), height);

Works like expected. You're a champ! Thank you so much!

GoToLoop

Re: Help! Why does this simple math return 0.0?

1 month ago

To get a minimum fuss, only 1 of the operands needs to be a float (or a double)
for the whole division operation result in a fractional value.
No need to convert both.

Also, for probable performance reasons, it's a safer bet to use
a Java's native cast operator rather than a conversion function.
So, instead of float( height), use -> ( float) height.

And all Processing's graphics functions use a float data-type as their coordinate parameters.
There's no need to convert any of them to int before passing them as arguments. Or vice-versa.

PhiLho

Re: Help! Why does this simple math return 0.0?

1 month ago

Don't forget to look at the Processing wiki, a good source of information, particularly:

In the last link, your trouble is described in item 7...

GoToLoop

Re: Help! Why does this simple math return 0.0?

1 month ago

To dispel any remaining doubts about the values of width & height in any circumstances, here's an example:
Take notice that stetchPath and dataPath() are invalid before setup() too.

{
  println("Width before setup() -> " + width);
}

void setup() {
  println("Width after setup() but before size() -> " + width);

  size(300, 200);

  println("Width after size() -> " + width);

  exit();
}

kodereakt..

Re: Help! Why does this simple math return 0.0?

1 month ago

Thanks for the extra information. :)

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