From: bukinm AT inp DOT nsk DOT su (Michael Bukin)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Translucence in SVGA Using Allegro
Date: Fri, 23 May 1997 12:22:01 GMT
Organization: BINP SD RAS
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References: <01bc671f$baf9a020$47e22499 AT syntaxlogic DOT earthlink DOT net>
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On 23 May 1997 01:45:03 GMT, "Alex Kain" <syntaxlogic AT earthlink DOT net>
wrote:

> Is using the translucence/lighting procedure in Allegro possible and/or
> practical in 640x480x256 svga?  I'd like to know how fast such a task would
> take, if it is possible.

It is possible.  Here is a patch for ex24.c from allegro2.2 sources.
To apply this patch, go to the directory where you unpack allegro
(there should be `examples' directory with ex24.c in it) and do:
patch < ex24.dif

Changes are:
1. you can choose video mode
2. background bitmap is scaled to the size of screen

To make it faster/smoother use different techniques for redrawing,
say, dirty rectangles.

--- start of ex24.dif ---
*** examples/ex24.c	Sun Jan 19 17:50:14 1997
--- examples/ex24.c~	Mon May 12 19:37:56 1997
***************
*** 35,44 ****
--- 35,46 ----
  
  int main(int argc, char *argv[])
  {
+    int c, w, h;
     PALLETE pal;
     BITMAP *s;
     BITMAP *temp;
     BITMAP *spotlight;
+    BITMAP *old_background;
     BITMAP *background;
     int i, x, y;
     char buf[80];
***************
*** 47,52 ****
--- 49,55 ----
     allegro_init(); 
     install_keyboard(); 
     install_mouse(); 
+    install_timer ();
  
     /* load the main screen image */
     if (argc > 1)
***************
*** 57,64 ****
        filename = buf;
     }
  
!    background = load_bitmap(filename, pal);
!    if (!background) {
        printf("Error reading %s!\n", filename);
        return 1;
     }
--- 60,67 ----
        filename = buf;
     }
  
!    old_background = load_bitmap(filename, pal);
!    if (!old_background) {
        printf("Error reading %s!\n", filename);
        return 1;
     }
***************
*** 77,88 ****
     create_trans_table(&trans_table, pal, 128, 128, 128,
callback_func);
  
     set_gfx_mode(GFX_VGA, 320, 200, 0, 0);
     set_pallete(pal);
  
!    s = create_bitmap(320, 200);
     spotlight = create_bitmap(128, 128);
     temp = create_bitmap(128, 128);
  
     /* generate a spotlight image */
     clear(spotlight);
     for(i=0; i<256; i++)
--- 80,110 ----
     create_trans_table(&trans_table, pal, 128, 128, 128,
callback_func);
  
     set_gfx_mode(GFX_VGA, 320, 200, 0, 0);
+    set_palette (desktop_palette);
+    if (!gfx_mode_select (&c, &w, &h))
+      {
+        allegro_exit ();
+        exit (1);
+      }
+ 
+    if (set_gfx_mode (c, w, h, 0, 0) != 0)
+      {
+        allegro_exit ();
+        printf ("error: can not set mode\n");
+        exit (1);
+      }
+ 
     set_pallete(pal);
  
!    s = create_bitmap(w, h);
     spotlight = create_bitmap(128, 128);
     temp = create_bitmap(128, 128);
  
+    background = create_bitmap (w, h);
+    stretch_blit (old_background, background,
+                  0, 0, old_background->w, old_background->h,
+                  0, 0, w, h);
+ 
     /* generate a spotlight image */
     clear(spotlight);
     for(i=0; i<256; i++)
***************
*** 101,114 ****
        blit(background, s, x, y, x, y, 128, 128);
        draw_trans_sprite(s, spotlight, x, y);
  
!       blit(s, screen, 0, 0, 0, 0, 320, 200);
  
     } while (!keypressed());
  
     readkey();
  
     /* generate an overlay image (just shrink the main image) */
!    stretch_blit(background, spotlight, 0, 0, 320, 200, 0, 0, 128,
128);
  
     /* select the translucency table */
     color_map = &trans_table;
--- 123,138 ----
        blit(background, s, x, y, x, y, 128, 128);
        draw_trans_sprite(s, spotlight, x, y);
  
!       blit(s, screen, 0, 0, 0, 0, w, h);
  
     } while (!keypressed());
  
     readkey();
  
     /* generate an overlay image (just shrink the main image) */
!    stretch_blit(old_background, spotlight,
!                 0, 0, old_background->w, old_background->h,
!                 0, 0, 128, 128);
  
     /* select the translucency table */
     color_map = &trans_table;
***************
*** 118,127 ****
        x = mouse_x - 64;
        y = mouse_y - 64;
  
!       blit(background, s, 0, 0, 0, 0, 320, 200);
        draw_trans_sprite(s, spotlight, x, y);
  
!       blit(s, screen, 0, 0, 0, 0, 320, 200);
  
     } while (!keypressed());
  
--- 142,151 ----
        x = mouse_x - 64;
        y = mouse_y - 64;
  
!       blit(background, s, 0, 0, 0, 0, w, h);
        draw_trans_sprite(s, spotlight, x, y);
  
!       blit(s, screen, 0, 0, 0, 0, w, h);
  
     } while (!keypressed());
  
--- end of ex24.dif ---