Photoshop Pattern Fill - Your Friend in Hatching
Drawing your own hatching would be incredibly tedious, even with all of Photoshop's tricks and perks that it has to offer. However, Photoshop does include a fair amount of hatch and crosshatch patterns that can easily fill large spaces with help from the paint bucket tool. Here's how you'd go about doing that.
Start with an area you'd like to fill in with your particular hatch pattern. Here I'll just use a majority of the canvas behind these few blank circles.
Select your paint bucket tool by pressing G. At the top of your screen you should now see a bar that looks like this:
Pull down on the tab that says "Foreground" and select "Pattern" instead. This simple action turns your paintbucket tool into the pattern fill tool. It should look like this now:
Now open your pattern menu by clicking on the pattern. Here you'll see a few default patterns. Nothing too special, and definitely nothing related to hatch patterns. However, if you click on the little triangle to the side, you'll see a flyout menu that allows you to select from different pattern packs that are included with Photoshop.
I went ahead and explored some of the packs, and I found a nice crosshatch pattern in "Artist's Surface" titled "Gause." Here's what it looks like when filled in behind the spheres: