The V36 graphics.library supports the ECS Agnus Blitter enhancements,
which provide for contiguous blits of up to 32768 x 32768 pixels at a
time.  Under the original chip set 1024 x 1024 was the maximum:

   BLTSIZE   W   A    Old Blitter size and start (window width, height)

        Bit   15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
        Use   h9 h8 h7 h6 h5 h4 h3 h2 h1 h0 w5 w4 w3 w2 w1 w0

            h = Height (10 bit height = 1024 lines  max)
            w = Width  (6 bit width  = 1024 pixels max)


Two new registers have been added which make larger blits possible:

   BLTSIZV   W   A       ECS Blitter V size

         Bit   15 14  12  12  11  10  09 08 07 06 05 04 03 02 01 00
         Use    0 h14 h13 h12 h11 h10 h9 h8 h7 h6 h5 h4 h3 h2 h1 h0

            h = Height (15 bit height = 32768 lines  max)


   BLTSIZH   W   A       ECS Blitter Horizontal size & start

         Bit   15 14  13  12  11  10  09 08 07 06 05 04 03 02 01 00
         Use    0  0   0   0   0  w10 w9 w8 w7 w6 w5 w4 w3 w2 w1 w0

            w = Width  (11 bit width  = 32768 pixels max)


With these two registers, blits up to 32K by 32K are now possible - much
larger than the original chip set could accept. The original commands are
retained for compatibility.  BLTSIZV should be written first, followed by
BLTSIZH, which starts the blitter.

The existence of the enhanced Agnus Blitter is reflected in the state of
the GfxBase->ChipRevBits bit definition GFXB_BIG_BLITS and is initialized
by the graphics.library at powerup. Note that the <hardware/blits.h>
constant MAXBYTESPERROW has been redefined to reflect the larger range of
legal blitter operations.

   About RastPort Sizes.
   ---------------------
   If the ECS Blitter is accessible, the graphics.library supports its
   use for all graphics functions including areafill, gels, line and
   ellipse drawing functions.

   If the ECS Blitter is not installed, programmers should limit the
   absolute size of their RastPorts to values that the old BLTSIZE
   register can address.

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