Gimp Draw Line Between Two Points

Done using GIMP 2.8 on Kubuntu Linux 18.04 LTS

Returning to the Tools on the left sidebar, another group of important tools is the Paint tools:

In a standard install, these are on the bottom of the sidebar, beginning with the Paint can icon, and they can also be found by going to the Tools menu. Note that if you move your cursor over an icon the tool tip will pop-up and give you the name. And all but one of them has a keyboard shortcut if you are into that sort of thing. They are:

Bucket Fill (Shift+B)
Blend (L)
Pencil (N)
Paintbrush (P)
Eraser (Shift+E)
Airbrush (A)
Ink (K)
Clone (C)
Heal (H)
Perspective Clone
Blur/Sharpen (Shift+U)
Smudge (S)
Dodge/Burn (Shift+D)

Basically, all of them work by dragging the cursor around like a paintbrush, which is why they are called Paint tools. And as we saw with the Selection tools, every tool has a specific properties selector on the bottom that appears when the tool is selected.

Now to be clear, drawing with a mouse cursor is not going to work well in a lot of cases. If you would be doing a lot of that kind of work you would be better off investing in a tablet and stylus, which give you much better control over your drawing. But if you only need to do occasional quick-and-dirty stuff a mouse can work if you are careful. And there are some aids. For example, trying to a draw a straight line with just the mouse cursor will never look very good. But if you hold down the Shift key, you can click on the beginning point of the line, then on the end point of the line, GIMP will draw a straight line between the two points. Keep holding down the Shift key and clicking and you will get a connected series of straight lines. This is handy. And if you hold down Control and Shift, you will get what is called a Constrained Straight Line, which will constrain the line to then nearest multiple of 15 degrees. This is great for getting perfectly vertical, horizontal, or diagonal lines.

Another concept to keep in mind here are Foreground and Background colors. Just below the Tools you will see two overlapping rectangles, with the top one covering part of the bottom one. The top one shows the foreground color (generally black if you haven't changed it), and the bottom one shows the Background color (generally White if you haven't changed it). If you click on one of the rectangles you can change the color. This matters because the Paint tools usually use the Foreground color for drawing.

Brief look at the tools

Here is a brief look at each of the tools. But please keep in mind that each tool has many optional property settings that fine tune what they do. I won't go into details here, but if you check the GIMP documentation (https://docs.gimp.org/2.8/en/) you can get all of the details.

Bucket Fill (Shift+B)

This fills an area with the current Foreground color, but if you hold down the Control key while clicking it fills with the Background color.

Blend (L)

This fills a selected area with a gradient blend of the Foreground and Background colors. You have two main areas of selection here, Gradient and Shape, which are set in the bottom Properties section when the tool is selected.

Pencil (N)

This tool and the Paintbrush tool are similar, differing mostly in that the pencil lines have hard edges and the Paintbrush tool has fuzzy edges. Hard edges are good when you need a high degree of precision. To get a straight line, click the beginning of the line, then hold down the Shift key, and click the end point of the line. By default, the line will be in the Foreground color. You can use the Background color though by holding down the Control key. Or if you like you can switch the colors around by click the double arrow head on the upper right of the Foreground/Background icon.

Paintbrush (P)

Very similar to the Pencil except that the line is a bit fuzzier on the edges. But this is a good opportunity to point out that you can select different brushes to use for both this tool and the Pencil tool by going to the Brushes section on the bottom of the Right sidebar.

Eraser (Shift+E)

As you might expect, this tool erases or removes color from an area. The result will be either the Background color coming through, or if there is an Alpha channel transparency will come through. This can be useful, for instance, when working with a masking layer (and we'll get to layers soon.)

Airbrush (A)

This tool emulates an airbrush for painting soft areas of color. It works by making the painting lighter. For example, if the Foreground is Red, the Airbrush will paint something closer to Pink.

Ink (K)

This tool imitates a pen, and can be used to create Calligraphy effects. You would have to experiment a little to see how this works, but as with a pen you can control things like the size of the nib and the angle at which it is applied.

Clone (C)

This tool lets you copy from an existing image or pattern. It is used a lot in repairing photos, for instance, where you can "paint over" an artifact in the image with nearby unaffected pixels. But it can also copy patterns. Note that is you are trying to copy from an image that has multiple layers, you need to select the layer first by holding down Control and clicking on that layer.

Heal (H)

This is related to the Clone tool, but is perhaps more powerful for small changes. It not only copies pixels over but also takes into account, through a clever algorithm, of the area surrounding the target. This can help, for example, in removing wrinkles from photographs.

Perspective Clone

Perspective is based on the idea of vanishing lines, one of the great breakthroughs of Renaissance painting, which is to draw the lines showing how things further away from you seem to get smaller and closer to each other because of the distance. You use this tool by drawing the vanishing lines, and then clone an image which will get smaller as it goes in the distance, and if you keep adding clones they also get closer together in the distance.

Blur/Sharpen (Shift+U)

This tool can either blur part of an image, or sharpen part of an image. Each pass of the cursor adds a little more effect. This can be useful for adding something to a small portion of an image, but if you want to affect the entire image there are filters better suited to that task. You can switch between Blur and Sharpen by holding the Control key.

Smudge (S)

This tool does what it says. If you were to write something in ink, or paint something, and then rubbed your thumb across it while the ink or paint was still wet, you would get a smudge. This tool emulates that by picking up color and mixing it in as you drag the cursor across an image.

Dodge/Burn (Shift+D)

This tool is used to lighten or darken pixels in an image. You can switch between lighten and darken with the Control key. There is also a Range selector in the Properties area that will restrict the tool to affecting only Darkest areas (Shadows), Mid-tones, or Lightest areas (Highlights). You can see how this might be useful for photo retouching.

Summary

This was a very brief introduction to the various painting tools in GIMP. As with the Selection tools, I would advise a little play and practice to see how each of these works. Create a White canvas, and start drawing on it. Create free-form lines, straight lines, and constrained lines, and see how brush selections affect things.

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Gimp Draw Line Between Two Points

Source: https://www.ahuka.com/gimp/paint-tools/