setAlpha() and push()/pop()

Phospheros

Should setAlpha() work as expected within a push/pop block? So far I've not had any success with this.

Modifying the example from the reference:

function setup() {
  ellipse(0, 50, 33, 33); // Left circle
  var c = color(204, 153, 0);

  push(); // Start a new drawing state
  strokeWeight(10);
  c.setAlpha(100);
  fill(c);
  translate(50, 0);
  ellipse(0, 50, 33, 33); // Middle circle
  pop(); // Restore original state

  fill(c);
  ellipse(100, 50, 33, 33); // Right circle
}

The right circle fill(c) is also alpha adjusted, even though outside push/pop. Is this by design?

KevinWorkman

This depends on what you mean by "as expected". How do you expect this to work?

I would not expect colors to be affected by push() or pop(). Those functions only affect transformations like translate() and rotate().

Phospheros

from the reference:

push() stores information related to the current transformation state and style settings controlled by the following functions: fill(), stroke(), tint(), strokeWeight(), strokeCap(), strokeJoin(), imageMode(), rectMode(), ellipseMode(), colorMode(), textAlign(), textFont(), textMode(), textSize(), textLeading().

KevinWorkman

Hmm interesting, guess I learned something new today!

But notice that the color.setAlpha() function is not listed in those functions.

jeremydouglass

In Processing(Java), pushMatrix() and pushStyle() are discrete -- in p5.js it looks like they are combined.

When you push and pop, the states of the global variables controlled by fill(), stroke(), tint() etc. are pushed / popped.

But in your case, you created a variable -- var c. That isn't a built-in Processing setting, it is your variable, and it isn't handled by push/pop.

Instead: set the fill state, push, change the fill state, then use pop to access the previous fill state.

Something like this...?

function setup() {
  var c = color(204, 153, 0);
  var c2 = color(204, 153, 0, 100);

  fill(c);
  ellipse(0, 50, 33, 33); // Left circle

  push(); // Start a new drawing state
  fill(c2);
  strokeWeight(10);
  translate(50, 0);
  ellipse(0, 50, 33, 33); // Middle circle
  pop(); // Restore original state

  ellipse(100, 50, 33, 33); // Right circle
}

Not that if you aren't drawing anything at all before you push then there is little point in using push.

Phospheros

I think I understand. Reassigning a variable changes its memory content regardless of setAlpha() or any other method, and push/pop has no bearing on that.

Thank you both for your time and your thoughts!