Fading

Fading

Neil Black

Member #7,867

October 2006

How can I do a fade in or fade out when I'm not using a palette? Also, how can I do a day/night cycle where the screen slowly darkens to night when I'm not using a palette?

gnolam

Member #2,030

March 2002

The easiest way is to draw a transparent black rectangle over the screen (buffer).

int alpha = 128; //arbitrary value for demonstration purposes

drawing_mode(DRAW_MODE_TRANS);
set_trans_blender(0, 0, 0, alpha);

rectfill(buffer, 0, 0, buffer->w, buffer->h, makecol(0, 0, 0));

blit(buffer, screen, 0, 0, 0, 0, SCREEN_W, SCREEN_H);

Quote:

Also, how can I do a day/night cycle where the screen slowly darkens to night when I'm not using a palette?

Depends on what kind of effect you're after. For a simple "everything turns darker" effect, see the code snippet above.

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Neil Black

Member #7,867

October 2006

Okay, in 16 bit mode I thought there wasn't an alpha value. I should have mentioned that I'm using a 16 bit color depth. Will that still work?

And the day/night cycle needs to fade to night, where the colors are darker and seem more bluish, and then back to day. I could have separate tiles for day and night, but there would be problems during the transition. Whatever I do has to be fast enough to run during game play.

Kauhiz

Member #4,798

July 2004

Quote:

Okay, in 16 bit mode I thought there wasn't an alpha value.

There isn't, that's why you have to supply it separately. In 32bpp you could have the alpha values stored in the bitmap.

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ImLeftFooted

Member #3,935

October 2003

const int cycles = 60 * 3;
for(int i = 0; i <= cycles; i++) {
 conf.beginScene();
 drawGame();
 Bitmap::rect(0, 0, 640, 480, Tint(1, 1, 1, float(i) / cycles);
 conf.flip();
}

How is my posting?

Neil Black

Member #7,867

October 2006

okay, dustin dettmer, you have several things I've never seen before in that code snippet, like Tint(...). is that an allegro function or just something you wrote that does what gnolam said? I also don't know what conf.beginScene() or
conf.flip() do. But I do understand the general idea... I think. I'd better do some experimenting.

GullRaDriel

Member #3,861

September 2003

It looks like openlayer thing.

"Code is like shit - it only smells if it is not yours"
Allegro Wiki, full of examples and articles !!

Neil Black

Member #7,867

October 2006

Openlayer? oh crap, more things-I-don't-understand-but-need-to! I thought I was through with that after I learned to tie my own shoes when I was 17

ImLeftFooted

Member #3,935

October 2003

Its actually from the Thing library. Which will soon be merged with OL (aka once I get some free time).

How is my posting?

Steve Terry

Member #1,989

March 2002

In 16-bit you can basically do a fast fade by packing two bytes into a 32-bit register. Here is the code I used:

1void Fade16(BITMAP *src, BITMAP *dest, int frame, int x, int y){
    unsigned long* read;
    unsigned long write;
    register unsigned long c1, c2;
    BITMAP *tmp = create_bitmap_ex(16, src->w, src->h);
    int i, j;
    int wid = src->w;
    acquire_bitmap(tmp);
    for(j = 0; j < src->h; ++j){
          read = (unsigned long*)src->line[j];
          write = bmp_write_line(tmp, j + y);
          for (i = wid; i; i-=2){
                // get two pixels;
                c1 = *read++;
                c2 = c1 & 0x7E0F81F;
                c1 &= 0xF81F07E0;
                // c1 / 32 * frame... then mask out the color components... 
                c1 = (((c1 >> 5) * frame) & 0xF81F07E0);
                // c2 * frame / 32... then mask out the color components... 
                c2 = (((c2 * frame) >> 5) & 0x07E0F81F);
                bmp_write32(write + x, ( c1 | c2 ));
                write+=4;
          }
    }
    bmp_unwrite_line(tmp);
    release_bitmap(tmp);
    blit(tmp, dest, 0, 0, x, y, tmp->w, tmp->h);
    destroy_bitmap(tmp);
29}

Well maybe not... I think I had a better function that didn't require a temporary bitmap... but meh?

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Neil Walker

Member #210

April 2000

fblend
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Neil Black

Member #7,867

October 2006

Gnolam's method seems to be the easiest, so I tried it first. Works perfectly! Thanks guys