Wondering...

[swestrup]

So, what would be the best way to write a DDA (Digital Differential Analyzer) for drawing lines on a Hex Grid? Note that I may want to play with various aspect ratios for the hexes, and/or allow a scene to be viewed from different angles (and not just from the obvious 6).

1. Divide the circle into 6 hexants, and have a routine thats a standard DDA using the two of the six 'axis' directions that lie on either side of the line. This will generate hex coordinates, to later be converted to (x,y) when drawing on the hex grid.
2. Do everything in (X,Y) coordinates, using a modified DDA that precomputes the differences due to the current orientation and aspect ratios.
3. a DDA is not the right tool for this job.

I'm thinking of using this as part of a computer RPG where you might have, for example a 'range 6' attack, and as you move the mouse, it shows the path your shot might take as you target various squares. So, I want it snappy and responsive. Oh, and this may get written in Flash Actionscript, so just saying 'do it any old way, the computer is fast enough' may not really be true.

Comments

[(Anonymous)]

(1) seems the simplest.

But what is DDA? Just the old algorithm to draw lines on a plotter that will only move its pen in eight directions? Or four? Or, in this case, six?

[swestrup]

Oops. My reply to you is below, and I'm guessing from your IP address that you're hendrikboom

[swestrup]

a DDA is a routine for drawing lines (and circles, and general conics) by means of finite differences. The best known example is Bresenham's DDA, although better formulations are known today.

One of these DDAs is the heart of any process today that draws lines on a screen, although its now often implemented in hardware.

[sps.livejournal.com]

(1). Of course the hexants in question are ±30° ones, not 0-60° ones. (Actually, it might be more reliable to use dodecants, just in case you ever find yourself dividing.)

[swestrup]

Yeah, I wondered about maybe using dodecants instead. The thing is, with (1), much of the math I'm saving by using a DDA is lost by then doing the conversion to Cartesian coordinates. With (2), I've got much greater complexity in code, but probably a faster run time. Then again, I may be over-optimizing.

[sps.livejournal.com]

Ah, I had understood that the task was to compute game mechanical lines, and maybe render them afterwards. If the task is to draw UI lines and maybe give them game mechanical interpretations afterwards, that's rather different!