Links
Download: http://www.whiteflute.org/wfrgss/?mode=view&realmId=1&pageId=24 ("「 Bitmap-EX ビットマップスクリプト(XP/VX/VXAce)」をダウンロードする" )
Docs: http://www.whiteflute.org/wfrgss/?mode=view&realmId=1&pageId=25
They have a dll to handle the image processing so it should be faster than trying to draw stuff in pure ruby.
Examples
reversing (that's the method name)

Whirlblur:

Usage
To set it up
1: copy the wfbitmap.dll into your game folder
2: replace your Main script with the one provided
3: copy the base and bitmap-ex scripts into your project
The library provides many useful functions for image-related things, such as drawing lines, polygons, and other things.
It also provides a png exporter, as well as support for GIF files (so you can actually have a GIF file playing on your screen). It works, but I'm not sure if it supports every possible GIF format out there. At least, it didn't load the ones I've tested properly (file was loaded, and was playing, but the pixels were off...)
For usage...most of it is just
Code:
Some of them are static methods thoughyour_bitmap.methodCode:
Just look at the Bitmap class.Bitmap.static_methodYou can draw pac-man

And textured polygons

See the method signatures in the docs.
It supports Ace, VX, and XP.