module ZXLib::Gfx

A module with Z80 Macros for common ZX Spectrum graphics tasks¶ ↑

Example:

require 'zxlib/gfx'

class Program
  include Z80
  macro_import  ZXLib::Gfx

          # invert pixel at 100, 100
          ld  l, 100
          ld  a, 100
          xytoscr(a, l, ah:h, al:l, s:b, t:c)
          inc b
          ld  a, 1
  shift1  rrca
          djnz shift1
          xor  [hl]
          ld   [hl], a
          ret
end

The coordinate system.¶ ↑

All of the Gfx routines, including Bobs, Clip, Draw, and Sprite8, are using the following screen coordinates system:

• The coordinates (0,0) are indicating the top-left corner of the screen.

• The vertical axis (y) is inversed - y increases towards the bottom of the screen. Hence e.g. 191 is the last visible pixel line and 23 is the last visible attributes cell row at the bottom.

• The horizontal axis (x) is normal - x increases towards the right edge of the screen. Hence e.g. 255 is the last visible pixel column and 31 (or 63 in hi-res) is the last visible cell column on the far right.