Alpha Blending problems
thehuggableone

Ok, I'm working on a platform shooter, and the edges of my graphics are a little pixelated, so, as I did in a backgammon game I wrote not too long ago, I'm using a function that creates an "anti-aliased" sprite by merging the real sprite with a separate alpha channel (same shape, but black and white with blurred edges). Below is almost exactly the same function I used for my backgammon game, however this one keeps giving me my sprite rendered as a black box.

I don't know what's going on. Masked draw is simply a call to masked blit. Is there something I'm missing? I've scoured my backgammon code and can't figure out what's going on. It would help if I actually understood what's going on with the transparency stuff, but it's not a necessity I don't guess.

I tried making a call to set_alpha_blender() before printing and even calling draw_trans_sprite() but that didn't work either. Any help would be wonderful, either in fixing my problem or suggesting a better way to do what I'm trying to do. I AM fairly new to game programming and could use all the help I can get.

Thanks

--Wes

1 
2void main()
3{
4 /*MAIN STUFF*/
5 daggy[0] = makeMasked("data/images/daggy_sprite.bmp","data/images/daggy_alpha.bmp", 128);
6 daggy[1] = makeMasked("data/images/daggy_sprite2.bmp","data/images/daggy_alpha2.bmp", 128);
7 
8 CSprite playerCharacter(daggy,1,0,0,0,0,0,100,100,0);
9 FixPlatformCollision(playerCharacter,background);
10 playerCharacter.update();
11 FixBoundsCollisions(playerCharacter);
12
13 playerCharacter.masked_draw(buffer);
14 
15 blit(buffer,screen,0,0,0,0,SCREENW,SCREENH);
16 while(!key[KEY_ESC}){}
17 /*MAIN STUFF*/
18}
19END_OF_MAIN();
20 
21BITMAP* makeMasked(char* image_file, char* alpha_file, int alpha)
22{
23 BITMAP *tempPiece;
24 BITMAP *sprite;
25 int c, a;
26
27 tempPiece = load_bitmap(image_file,NULL);
28 sprite = load_bitmap(alpha_file,NULL);
29
30 drawing_mode(DRAW_MODE_TRANS, NULL, 0, 0);
31 set_write_alpha_blender();
32
33 for (int y=0; y<sprite->h; y++) {
34 for (int x=0; x<sprite->w; x++) {
35 c = getpixel(sprite, x, y);
36 a = getr(c) + getg(c) + getb(c);
37 a = MID(0, a/2-alpha, 255);
38 putpixel(tempPiece, x, y, a);
39 }
40 }
41
42 drawing_mode(DRAW_MODE_SOLID, NULL, 0, 0);
43
44 destroy_bitmap(sprite);
45 return tempPiece;
46}

Arthur Kalliokoski

I'm just taking a wild guess here, but stick in a couple lines in the program to save the masked bitmaps to .tga files, then make a little allegro utility to display these and call getpixel() on mouse clicks to display the rgba values.

Thread #587021. Printed from Allegro.cc