Very basic question about pixels

Cap

How do you find the center pixel?

Say I have the width set at an even number of pixels, 8.

Pixels going across pizel 0, pixel 1... to pixel 7.

I would think initially that to get to the centre, you'd say (8-1)/2 but this would be 3.5, and there's no pixel 3.5, so how would processing resolve this? Round up to pixel 4? And settle for an off-centre pixel?

Or should I say 8/4, instead of minusing 1 for the zero that gets counted?

GoToLoop

• There's no exact center for an even quantity, only for odd. ^#(^
• Let's say width is 800, so you've got a 0-799 range.
• Centered pixel coordinate would be 800/2 = 400. But 399 would be valid too.
• That is, both 399th & 400th would both be the centered pixels for an even width.
• Now w/ width = 801, which is a 0-800 range, the 400th pixel coordinate is the exact center.
• Left range is 0-399, right range is 401-800, and center is 400th. :-B

Cap

Thanks so much for responding to what I was starting to think was just me being ocd pedantic.

So it's like the two center pixels become a double sized Center Pixel? If you coloured it with stroke(0), and then zoomed it to see the individual pixels with grid lines, there would be two coloured pixels?

GoToLoop

So it's like the two center pixels become a double sized Center Pixel?

• Not like that. It just means that for an even quantity of pixels, they're evenly split in half.
• For example, let's say you've got resolution 800x600: size(800, 600);
• So you've got width = 800 (0-799 range) & height = 600 (0-599 range).
• For width, its left side got 400 pixels (0-399). Right side got 400 pixels too (400-799).
• For height, its top side got 300 pixels (0-299). Bottom side got 300 pixels too (300-599).
• Therefore both the 399th & 400th pixels are in the middle width of the canvas.
• Same for height: both the 299th & 300th pixels. :-B

Cap

Follow up question in the same vein:

Working with that pixel coordinate x=400 as the centre pixel coordinate in an even split, pixel399 on the left and pixel400 on the right, how does it work if I want to use this point as centre if I do something like rectMode (CENTER) with a width of 3 pixels. Which side gets the extra pixel?

GoToLoop

Dunno the algorithm they use for rect() rendering when rectMode() is set to CENTER. :-??

Cap

Thanks. I thought I was missing something. Going through Learning Processing, but I wanted to figure this out before I moved on because I thought it might be important #:-S