# Retrograph-0.5

**URL:** <https://www.ruby-forum.com/t/retrograph-0-5/172670>\
**Category:** Ruby\
**Created:** [July 25, 2009, 1:39am UTC](https://www.ruby-forum.com/t/retrograph-0-5/172670 "2009-07-25T01:39:10Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![mental](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/c77e96/32.png) [@mental](https://www.ruby-forum.com/u/mental)\
**Post date:** [July 25, 2009, 1:39am UTC](https://www.ruby-forum.com/t/retrograph-0-5/172670/1 "2009-07-25T01:39:10Z")

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== What is Retrograph? ==

Retrograph is a Ruby library which emulates the video  
display unit from a hypothetical late-80s 8-bit game  
console. It is similar in capability to the Sega Master  
System’s VDP, with some additional features and direct  
support for text modes.

Retrograph doesn’t do its own screen output but rather  
works with other libraries. Currently, it supports  
Ruby/SDL, but other output targets are planned for the  
future.

== Where can I get it? ==

Retrograph is available via RubyGems, or via Rubyforge  
downloads:

[http://rubyforge.org/frs/?group\_id=8410](http://rubyforge.org/frs/?group_id=8410)

Cursory documentation is available on the  
corresponding github wiki:

[http://wiki.github.com/mental/retrograph](http://wiki.github.com/mental/retrograph)

== Feature Overview ==

- 256x244 pixel display
- 16k VRAM
- 64 colors total
- max 31 simultaneous colors (16 background, 15 sprite)
- 40x25 and 32x28 text modes
- 32x32 tile background, 8x8 pixel tiles
- 64 8x8 sprites, max 8 per scanline

== Usage ==

Retrograph’s simulated Video Display Unit (or VDU) is  
represented by an instance of the Retrograph::VDU class.  
You can interact with the VDU by writing byte strings  
into its memory using Retrograph::VDU#write, which takes  
a start address (in the VDU’s 16-bit address space) and  
a string to write. The method Retrograph::VDU#write\_byte  
is also provided for writing individual bytes.

(See the wiki for a map of memory locations.)

To render a frame of video with SDL, use  
Retrograph::VDU#render\_frame\_sdl, which returns an  
SDL::Surface containing the VDU output. The returned  
surface remains valid until the next call to  
Retrograph::VDU#render\_frame\_sdl on the same VDU instance.

Scanline-based effects are possible if you provide a block  
to Retrograph::VDU#render\_frame\_sdl. Ordinarily, rendering  
will not begin until the block completes, but within the  
block you can call Retrograph::VDU#wait\_scanlines to render  
a given number of scanlines before continuing. This allows  
you to make changes to the VDU state part-way through  
rendering a frame.

For example, if we wanted palette entry 0 to be blue within  
the top half of the display and red within the bottom half  
of the display, we could write:

require ‘retrograph/sdl’

vdu.write\_byte(0x7f00, 0x03)  
output = vdu.render\_frame\_sdl do  
vdu.wait\_scanlines(Retrograph::DISPLAY\_HEIGHT/2)  
vdu.write\_byte(0x7f00, 0x30)  
end

(For display, is still necessary at this point to copy the  
output surface to the screen.)

Love,  
-mental