🚀 go-pugleaf

In article <1138972342.009774.60130@g44g2000cwa.googlegroups.com>,
KevinGPO <kevingpo@hotmail.com> wrote:
>I just programming Duke Nukem 3D source code and trying to understand
>the drawing graphics routines. In the (game folder) game.c: main()

Haven't looked at them carefully enough to answer you.

[...]
>Other queries:
>1. What is significant with show2dsector[i>>3]&(1<<(i&7)) ? I see this
>pattern all over the place to test/decide whether to show a map object
>or not. However I do not understand why bit-shift to the right 3
>places, and bitmask AND on 7, then bit-shift to left by 1 place?

I'm answering on the fly, so please excuse any misformatting.

He's using the lower 3 bits of "i" to select a bit in the rest of i.  

>
>2. What is significant with calling the sintable[(spr->ang)&2047] with
>2047 all the time?
>

It masks out unwanted bits that are too high, thus it prevents the table from being accessed with too-large indexes by accident.  


HTH.

Tom, the calm-eyed visionary