ALLEGRO_LOCKED_REGION - Allegro 5 API

       Users  who  wish  to  manually  edit  or  read  from  a  bitmap  are  required  to  lock  it  first.  The
       ALLEGRO_LOCKED_REGION structure represents the locked region of the bitmap.  This call will work with any
       bitmap, including memory bitmaps.

              typedef struct ALLEGRO_LOCKED_REGION {
                 void *data;
                 int format;
                 int pitch;
                 int pixel_size;
              } ALLEGRO_LOCKED_REGION;

       • data points to the leftmost pixel of the first row (row 0) of the locked region.  For blocked  formats,
         this points to the leftmost block of the first row of blocks.

       • format indicates the pixel format of the data.

       • pitch  gives  the  size  in bytes of a single row (also known as the stride).  The pitch may be greater
         than width * pixel_size due to padding; this is not uncommon.  It is also not uncommon for the pitch to
         be negative (the bitmap may be upside down).  For blocked formats, `row' refers to the row  of  blocks,
         not of pixels.

       • pixel_size  is  the  number of bytes used to represent a single block of pixels for the pixel format of
         this locked region.  For most formats (and historically, this used to be true for all formats), this is
         just the size of a single pixel, but for blocked pixel formats this value is different.

       ALLEGRO_LOCKED_REGION - Allegro 5 API

al_lock_bitmap(3alleg5),            al_lock_bitmap_region(3alleg5),            al_unlock_bitmap(3alleg5),
       ALLEGRO_PIXEL_FORMAT(3alleg5)

Allegro reference manual                                                          ALLEGRO_LOCKED_REGION(3alleg5)

              #include <allegro5/allegro.h>

              typedef struct ALLEGRO_LOCKED_REGION ALLEGRO_LOCKED_REGION;