SDL, using PNG files with alpha transparency...

Hi,

I'm going to program a simple 2D platform independent game using SDL.
My development environment is Win32 (XP) with MS VC++ .NET.

All sprites uses 32bit depth and will be stored in a format which supports alpha channels.
Instead of color keying I want to use real transparency, using the alpha channel of the sprite.

Does anybody know how to use PNG/PSD files with SDL ?



TIA,

Frank
--
ats uxThemePatcher XP .NET

© 2003 by animalTactics
http://kickme.to/ats

Don't know about the SDL but the standard (pretty standard) format for
sprites with alpha channels is BMP


"Frank Hoffmann" <atomicStrike@gmx.de> wrote in message
news:bhg4c1$c1ds$1@ID-77060.news.uni-berlin.de...
Hi,

I'm going to program a simple 2D platform independent game using SDL.
My development environment is Win32 (XP) with MS VC++ .NET.

All sprites uses 32bit depth and will be stored in a format which supports
alpha channels.
Instead of color keying I want to use real transparency, using the alpha
channel of the sprite.

Does anybody know how to use PNG/PSD files with SDL ?



TIA,

Frank
--
ats uxThemePatcher XP .NET

© 2003 by animalTactics
http://kickme.to/ats

You'll be very impressed with SDL .PNG alpha support, if you can get you're
paint software to do what you want.

First of all, I use PSP (7 or 8) and these instructions will apply to this
package only (and to SDL).

In PSP, choose File->Export->PNG Optimizer, then click the tranparency tab.
Set it to "Alpha channel transparency".
Click OK, then name the file.

Now, if you're art has a proper transparent background (in PSP transparency
looks like a checkerboard, I think in photoshop it looks like a crosshatch
pattern?), all you need to do is load the png via the normal sdl_img
functions. SDL is smart enough to set the color key for a new surface if the
..PNG you're loading from has the color key field (in it's header) set, and
the above instructions guarantee that PSP saved the file with this info.

Here's the best part!

SDL will also, automatically use whatever alpha channel is available in the
source image when blitting! This was a real pleasant surprise when I found
it out on my last game... I was building some lazy clouds that floated above
the player... I was fooling with transparency and I accidently export'ed the
png with about 50% alpha transparency. This built in support for alpha
blending let me implement the coolest effects in my game...

Tony


"Frank Hoffmann" <atomicStrike@gmx.de> wrote in message
news:bhg4c1$c1ds$1@ID-77060.news.uni-berlin.de...
Hi,

I'm going to program a simple 2D platform independent game using SDL.
My development environment is Win32 (XP) with MS VC++ .NET.

All sprites uses 32bit depth and will be stored in a format which supports
alpha channels.
Instead of color keying I want to use real transparency, using the alpha
channel of the sprite.

Does anybody know how to use PNG/PSD files with SDL ?



TIA,

Frank
--
ats uxThemePatcher XP .NET

© 2003 by animalTactics
http://kickme.to/ats

Hi,

thanks for all answers.
I want to recommend this library for SDL:

http://www.libsdl.org/projects/SDL_image/

As Tony mentioned, using .png with alpha channels allows you to implement
fantastic effects in your game. Maybe I will use this for a particle generator,
or lightning effects...

Frank