Why is only a part of the window used, if stroke's opacity is between 0 and 255?

Programming Questions

yip4711

Why is only a part of the window used, if stroke's opacity is between 0 and 255?

in Programming Questions • 2 years ago

Hi,

I've just started playing around with Processing and I can't even get the simplest script to work! Please, take a look at the screenshot below.

If I change the opacity value to 255, then I get a fully orange window. If I change the opacity value to 0, then I get a fully white window. However, if I use any opacity value in between, then most of the window stays white and the rectangles on the left are shades of orange. The orange shapes never change even if a close and restart Processing.

What could be happening here?

Replies(2)

amnon.owed

Re: Why is only a part of the window used, if stroke's opacity is between 0 and 255?

2 years ago

There are some rounding (?) issues with points and lines in Processing (the same kind of issue has been reported for repeating lines). A workaround in your example is to use strokeWeight(1.1); to make sure each point is visible.

Also, you might wanna take a look at using the pixel array instead for these type of manipulations. It's faster, more accurate and more flexible.

PhiLho

Re: Why is only a part of the window used, if stroke's opacity is between 0 and 255?

2 years ago

You know, it is hard to run screenshots... You should give code that can be copied/pasted.

Now, that's interesting and surprising... I can reproduce that in 1.5 and 1.2.1.
If we add smooth() to the mix, it behaves correctly.
I supposed there was a strange interaction of anti-aliasing, but even if I space out the pixels, we get the same rendering.
Very strange...

I think it is a Java2D issue, as in P2D mode, the problem disappears.

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