Can anyone help me out with alpha channel issue? I have created an image using PS5.5 and made an alpha channel for my selection. As a next step, I have saved this image as a Targa (TGA) format including alpha channel.

My question is how do I load this image back to my Allegro project? I want to display it over other backgrounds so it would create transparency in the areas where it should. I have seen some DirectX demos a while ago where a particle system would be using some alpha channels (it looked really nice.)

I would really appreciate if someone had a link or an example of how to accomplish alpha channel within the Allegro.

Best regards,
Marius

bmp = load_bmp("blah.tga", NULL);
set_alpha_channel();
blit(bmp, buffer, 0, 0, 0, 0, bmp->w, bmp->h);

I mean it's not hard

To load the image you must be sure that it's loaded in a 32bpp bitmap. For that, you have to disable color conversion:

set_color_conversion(COLORCONV_NONE);
image_with_alpha = load_bitmap("file.tga", NULL);
set_color_conversion(COLORCONV_TOTAL);

To blit you just have to enable alpha blending:

drawing_mode(DRAW_MODE_TRANS, NULL, 0, 0);
set_alpha_blender();
// blit the alpha image
solid_mode();

[edit]

Steve, you just made that up, didn't you?

>_< I had alpha channel in my mind when I wrote that... it's a typo yes

Thank you guys so much! This is one of the best places to get some answers :-)

You better believe it

Worked like a charm

WE rule, and GameDev drools

Hahaha. Sorry to interrupt the scheduled victory dance, but what's the point of draw_trans_sprite() if a regular blit does the same thing?

Steve Terry said:

    bmp = load_bmp("blah.tga", NULL);
    set_alpha_channel();
    blit(bmp, buffer, 0, 0, 0, 0, bmp->w, bmp->h);

I wouldn't look much to Steve's code

:'(
I wrote it in a hurry and wasn't thinking
/me goes back to RTFM :P

Actually, the docs are a bit vague about this:

but if you go to the blitting and sprites section, only draw_trans_sprite (and draw_lit_sprite) mentions it's affected by the current drawing mode.

IIRC blit is not affected by draw_mode, but the docs say the opposite (but it wouldn't have sense to have two functions, draw_sprite and draw_trans_sprite).

Eh? Maybe I'm missing something, but the snippet you posted says "not the text output, blitting, or sprite drawing functions".

Well, I had to replace blit with draw_trans_sprite function. Thanks to the fast response from Steve and Oscar. Thank you guys :-)

It was very late when I read that.

Hahaha! I only laugh because I've been there...