Nothing breaks it being pixel art, as long as you are in full control of the outcome.
My favorite method is copy + paste.

More important than the question 'how to dither?' is 'why to dither?'.

Sounds like you are not using a program that has features to help you dither.
GrafX2 and ProMotion both support this. In Grafx2, you can access the feature via FX->Sieve.

Here's something I threw together in a few minutes using Contour Fill, Sieve, and a few different brush sizes.



I wouldn't have any problem considering that pixel art, however rushed it is.

This type of method is commonly used by pixel artists who choose to do a lot of dithering. It's really quite easy, and you still have the opportunity to adjust things exactly as you want them.

The only reason why you might avoid this type of method is if your dithering is irregular/ 'stylistic' (like this, for example). But you're talking about perfect patterns, so that shouldn't be relevant for now.

EDIT:
You can use various other related methods (for example, in Photoshop or GIMP, you can clone from a pattern or layer), but be aware that this is more cumbersome -- you have to update the source pattern any time you want to change dithering color, as opposed to simply changing the pen color (in Grafx2 or ProMotion). Programs that -explicitly- support pixel dithering are the most comfortable to work with.

Copy+Paste is basically the desperation method.. I would not use it unless forced to, as it's quite repetitive and cumbersome. At smaller sizes it's often more troublesome than simply plotting the individual pixels.



In response to the question of 'why to dither': You can think of the more 'generic' perfect patterns as a type of airbrush tool, which should inform you that you are best off using this in lower-detail areas, where smoothness is more important than crispness. Less generic patterns can also add texture / stylistic elements.


Edited by neota - 21 May 2014 at 8:35pm

Okay, different meaning for 'stylistic' dithering than I meant. You can definitely do any dither pattern you want using Photoshop or GIMP, but the type of stylistic dithering I mentioned cannot be done by a simple pattern, because it needs to adapt to its surroundings.

Here is a quick example I whipped up:



A more involved example is ilkke's "Clockwork whistler", which has both small-scale conventional dithering, and larger-scale stylistic dithering.

There's not an absolute consensus, but mostly people are willing to agree that if you have control of every pixel, then it's pixel art. Since pattern fills and etc are fine, that boils down to 'stray/meaningless pixels are suspicious, don't leave stray pixels.'

Contour fill is a mode of the normal freehand drawing tool. Instead of plotting the brush continuously as you move the mouse, it tracks the shape you draw, and when you release the mouse button, fills it.
You can access it by rightclicking on the draw tool icon until it looks like a filled polygon.


Edited by neota - 23 May 2014 at 5:44am