SRCCOLORKEY code

SDL Development
1

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Here it is (please note, it is included in c++ classes but i have cut&pasted
it here)

  1. setvideomode:
    surface = SDL_SetVideoMode( x_res, y_res, 32, SDL_SWSURFACE ); // nothing
    changes if i use SDL_HWSURFACE.

  2. next to this, i have a “SpriteData” class which does the following:

    sprite[x] = SDL_CreateRGBSurface( SDL_SWSURFACE, width, height,
    SDL_GetVideoSurface()->format->Rmask,
    SDL_GetVideoSurface()->format->Gmask,
    SDL_GetVideoSurface()->format->Bmask,
    SDL_GetVideoSurface()->format->Amask );

    SDL_SetColorKey( sprite[x], SDL_SCRCOLORKEY, SDL_MapRGB(sprite[x]->format,
    0,0,0) );

    (i also tried to call SDL_DisplayFormat, but no luck)

  3. I copy pixel data on the surface:

for ( y = 0; y < height; y++ )
{
tmp = &sprite[x]->pixels[ ywidth ];
memcpy( tmp, row_bytes[y], width4);
}

(please note: the data is loaded from a png using libpng)

  1. then i create 4 intermediate surface:

    buffer[y] = SDL_CreateRGBSurface(SDL_SWSURFACE, x_res/4, y_res/4,
    SDL_GetVideoSurface()->format->Rmask,
    SDL_GetVideoSurface()->format->Gmask,
    SDL_GetVideoSurface()->format->Bmask,
    SDL_GetVideoSurface()->format->Amask );

    (i dont set any colorkey here)

  2. next, during gameplay, i copy the sprites on the intermediate surfaces,
    there are also all the calculations needed to copy a surface into adjacent
    intermediate surfaces if the sprite overlap two or more of them, but i omit
    it here:

    rectd.x = x_pos;
    rectd.y = y_pos;
    rects.x = start_x;
    rects.y = start_y;
    rects.w = end_x-start_x;
    rects.h = end_y-start_y;
    SDL_BlitSurface( buffer[y], &rectd, sprite->GetSurface(x), &rects);
    (here the color keyng is supposed to work if i am not wrong!)

  3. last, after all the sprites update is done, i update the video surface:

    SDL_BlitSurface( surface, &rectd,buffer[y], &rects);

END) i had not transparencing. I have also tested the following:
a) the color (0,0,0) is present in the sprite(s) and it is in the correct
position in the image (checked with gimp)
b) after loading the sprites, the row_bytes contains exactly the same values
as found in gimp (es: 0,0,0 for the first top left pixel)

Whats strange is the pixel format, it is 32bit but the masks are:
r: 0x00ff0000
g: 0x0000ff00
b: 0x000000ff
a: 0x00000000

seems no alpha avalaible. Why?
thank you…

!
Willy Gardiol - @Willy_Gardiol
goemon.polito.it/~gardiol
Use linux for your freedom.

"Ho visto quest’anno a Kabul bambini
dilaniati dalle mine: grumi di garza
e sangue su brande sudice in lazzaretti.

Bambini i cui occhi e i cui orecchi non 
hanno mai visto un disegno, ascoltato 
una musica."

Vauro, Appunti di guerra (2002)

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