Accesing to one bit from an array, and Edit it
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Hello there!
SO, I'm making an sprite editor program, and I want help on the most criticalk code: Accessing bits.

Our PSrite system (on casio FXes), sprites are coded directly by bits:

Example with a sprite of 8*8

11111111
11111111
11111111
11111111
11111111
11111111
11111111
11111111 //the 1 is to say "bit used"

and sprite of 9*9
1111111110000000// 0 are unused and must be
1111111110000000
1111111110000000
1111111110000000
1111111110000000
1111111110000000
1111111110000000
1111111110000000
1111111110000000// see the bits lost
// Here, I I want to get for example the 10th bit, I must get the first 1 of the second line

And I must be able to access to any bit of size of sprite, If you understand.

I have already found some parts of code, but nothing that important


Code:
int w,h; //size
int x,y; //position

w/8+1; //would give me the number of bytes used by line, I
(x*y)/w; // would give me the line to edit
suppose


I don't know how to end my topic, but I'll thank any help from you!
See ya!
Firstly,
Code:
typedef struct
{
  union
  {
    uint8_t data;
    struct
    {
      uint8_t b7 : 1;
      uint8_t b6 : 1;
      uint8_t b5 : 1;
      uint8_t b4 : 1;
      uint8_t b3 : 1;
      uint8_t b2 : 1;
      uint8_t b2 : 1;
      uint8_t b0 : 1;
    };
  };
} bitfield8_t;


Bits are from right to left in a byte, starting from 0. To use it, have
Code:
bitfield8_t bf;
bf.data = (byte); // your overflow


You can access bits directly by using bf.b(0 through 7).
[nikky] the free market will decide who gets to be on the channel and who isn't
Array(16).join("wat" - 1) + " Batman!"
CC20: Air
A macro like this would work:


Code:
#define get_bit(input, bit) ((input & (1<<bit))>>bit)
R O F L M A O
O
F
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A
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Code:

unsigned char drawmap(unsigned char* spr, unsigned char w, unsigned char h)
{
   int x, y;
   unsigned char byt, pix;
   for(y = 0; y < h; y++)
   {
      for(x = 0; x < w; x++)
      {
         byt = spr[  (w*y + x)/w + x/8];
         pix = get_bit(byt, (x%8));
         if(pix)
         ML_rectangle(2*x, 2*y, 2*x+1, 2*y+1, 0, BLACK, BLACK);
      }
   }
}


With some tests, I think I almost got it...

EDIT :Test oncalc
  
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