Question

I am currently using Bresenham’s algorithm to draw lines but they are (of course) one pixel in thickness. My question is what is the most efficient way to draw lines of arbitrary thickness?

The language I am using is C.

Answer 1

I think the best way is to draw a rectangle rather than a line since a line with width is a two dimensional object. Tring to draw a set of parallel lines to avoid overdraw (to reduce write bandwidth) and underdraw (missing pixels) would be quite complex. It’s not too hard to calculate the corner points of the rectangle from the start and end point and the width.

So, following a comment below, the process to do this would be:-

1. Create a rectangle the same length as the required line and width equal to the desired width, so (0,0) to (width,length)
2. Rotate and translate the rectangles corner coordinates to the desired position using a 2D transformation
3. Rasterise the rotated rectangle, either using a hardware accelerated renderer (an OpenGL quad for example*) or use a software rasteriser. It can be rendered using a quad rasteriser or as a pair of triangles (top left and bottom right for example).

Note *: If you’re using OpenGL you can also do Step 2 at the same time. Of course, using OpenGL does mean understanding OpenGL (big and complex) and this application may make that a tricky thing to implement at such a late stage in development.