pngscreenshot 1.0

pngscreenshot 1.0

Overview

Today was another one of those lazy days where I couldn't bring myself to get anything constructive done on the game. So instead I added the ability to take a screenshot from inside my game, and write it out to disk. DirectX 8 makes this easy; you just GetFrontBuffer() and D3DXSaveSurfaceToFile().

Unfortunately, D3DXSaveSurfaceToFile() only supports BMP and DDS files, and won't write compressed files. And since GetFrontBuffer() only supports D3DFMT_A8R8G8B8, a BMP screenshot of a 1600x1200 screen is over 7.6MB! Eek!

Since I was already using Zlib, I realized that all I had to do was add libpng to my project and hack out a file writer from their example code. An hour later and it was up and running, generating simple but correct PNG files. Now those same 1600x1200 screenshots are only about 600k. Ahh, much better!

But I still wasn't done procrastinating for the day. I decided to turn the code into a cheap and sleazy library for Flipcode, and post it here. To share with the whole world. Hooray!

The pngscreenshot web page is here:

http://www.midwinter.com/~larry/programming/pngscreenshot/

And you can download a fresh copy of the source code here:

http://www.midwinter.com/~larry/programming/pngscreenshot/pngscreenshot.zip

Notes on pngscreenshot

In order for pngscreenshot to work, you'll need to link to Zlib and libpng in your project. libpng is the reference implementation for PNG; Zlib is the compression library used by libpng. Both are released under a very liberal license; it's "MIT-style", where you may use the source code for any purpose you like as long as you don't sue 'em and you leave their copyright notices alone. (Much the same as the license for pngscreenshot!)
In my game, Zlib and libpng each add about 22k, and pngscreenshot adds about 1k. So the total size added is about 45k. And isn't that worth it, for cool PNG screenshots?
This code was written using DirectX 8, and won't compile out-of-the-box for older versions (and maybe not even newer versions, I dunno). Send in your diffs for other versions!

What are PNG files?

The authors of PNG do a much better job describing it than I can. But, in a nutshell, a PNG file is a lossless compressed image file format. Unlike JPG files, PNG files are lossless—a PNG file will reproduce the original file exactly. Unlike GIF files, PNG files are unencumbered by patents, and support truecolor images (GIF is limited to 256 colors).

How To Use pngscreenshot

First, download, build, and link to both Zlib and libpng. libpng is the reference implementation for PNG; Zlib is the compression library used by libpng. Both are released under a very liberal license; it's "MIT-style", where you may use the source code for any purpose you like as long as you don't sue 'em and you leave their copyright notices alone.
Include pngscreenshot.cpp in your project.

Add the following prototype to your header file somewhere:

extern void screenshot(LPDIRECT3DDEVICE8 display, int width, int height, char *filename=NULL);

Any time you want to generate a screenshot, call screenshot(). If you pass in NULL for the filename, it'll write a file named screenshot.#.png to the current directory, where # is an ever-increasing number.

And you're ready to rock!

Licensing

Here's the license:

/*
** [BEGIN NOTICE]
**
** Copyright (C) 2003 Larry Hastings
**
** This software is provided 'as-is', without any express or implied warranty.
** In no event will the authors be held liable for any damages arising from
** the use of this software.
**
** Permission is granted to anyone to use this software for any purpose,
** including commercial applications, and to alter it and redistribute
** it freely, subject to the following restrictions:
**
** 1. The origin of this software must not be misrepresented; you must not
**    claim that you wrote the original software. If you use this software
**    in a product, an acknowledgment in the product documentation would be
**    appreciated but is not required.
** 2. Altered source versions must be plainly marked as such, and must not be
**    misrepresented as being the original software.
** 3. This notice may not be removed or altered from any source distribution.
**
** The pngscreenshot homepage is here:
**		http://www.midwinter.com/~larry/programming/pngscreenshot/
**
** [END NOTICE]
*/

In non-legalese, my goal was to allow you to do anything you like with the software, except claim that you wrote the original version. If my license prevents you from doing something you'd like to do, contact me (my email address is in the source) and we can discuss it.

Version History

1.0: Thursday, August 14^th, 2003
Initial public release.

Happy screenshooting!

larry