Check to see if a bitmap is a solid color

Check to see if a bitmap is a solid color

Ceagon Xylas

Member #5,495

February 2005

Like the topic title indicates, I'm asking what is the fastest way to check if a bitmap's a solid color?
I'm trying to check and see if a 32x32 bitmap is solid magic pink.

miran

Member #2,407

June 2002

EDIT: nm, I misunderstood the question.

The real answer: two for loops.

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Ceagon Xylas

Member #5,495

February 2005

And getpixel I assume? I guess it's not too slow for only loading bitmap routines.

miran

Member #2,407

June 2002

You can also use direct access. Or one of the colour depth specific access functions that don't do bounds checking.

_getpixel32()

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Ceagon Xylas

Member #5,495

February 2005

Okee doke. Thanks

GullRaDriel

Member #3,861

September 2003

Perhaps this from exfire.c, with some little change you can adjust it to fit your need:

 /* It is even faster if we transfer the data in 32 bit chunks, rather
  * than only one pixel at a time. This method may not work on really
  * unusual machine architectures, but should be ok on just about
  * anything that you are practically likely to come across.
  */
 while (!keypressed()) {
    acquire_screen();
    draw_bottom_line_of_fire();
9 
    bmp_select(screen);
11 
    for (y=64; y<SCREEN_H-1; y++) {
 /* get an address for reading line y+1 */
 address = bmp_read_line(screen, y+1);
15 
 /* read line in 32 bit chunks */
 for (x=0; x<SCREEN_W; x += sizeof(uint32_t))
    *((uint32_t *)&temp[x]) = bmp_read32(address+x);
19 
 /* adjust it */
 for (x=0; x<SCREEN_W; x++)
    if (temp[x] > 0)
       temp[x]--;
24 
 /* get an address for writing line y */
 address = bmp_write_line(screen, y);
27 
 /* write line in 32 bit chunks */
 for (x=0; x<SCREEN_W; x += sizeof(uint32_t))
    bmp_write32(address+x, *((uint32_t *)&temp[x]));
    }
32 
    bmp_unwrite_line(screen);
    release_screen();
 }
36 
 free(temp);
38 
 return 0;
40}

This article from Gamedev about digital processing can help too for implementing gaussian blur.
_

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

Onewing

Member #6,152

August 2005

//Untested 
bool is_solid_color(BITMAP *src, int col)
{
  int x = 0, y = 0;
  int check_col = -1;
  while(y < src->h && (check_col = getpixel(src,x++,y)) == col)
    if(x == src->w) {  x = 0; y++;   }

  if(check_col != col)
    return false;
  return true;
}

Funny thing about this is the worst case scenario is when the bitmap IS the given solid color.

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Rampage

Member #3,035

December 2002

Onewing Phipps:

bool is_solid_color(BITMAP *src, int col)
{
  int x = 0, y = 0;
  int check_col = -1;
  while(y < src->h && (check_col = getpixel(src,x++,y)) == col)
    if(x == src->w) {  x = 0; y++;   }

  // just a minor improvement
  return check_col == col;
}

-R

Ceagon Xylas

Member #5,495

February 2005