Initial data commit

Task/Bitmap-Bresenhams-line-algorithm/Forth/bitmap-bresenhams-line-algorithm.fth

@@ -0,0 +1,48 @@
+defer steep         \ noop or swap
+defer ystep         \ 1+ or 1-
+
+: line ( x0 y0 x1 y1 color bmp -- )
+  { color bmp }
+  rot swap
+  ( x0 x1 y0 y1 )
+  2dup  - abs >r
+  2over - abs r> <
+  if         ['] swap \ swap use of x and y
+  else 2swap ['] noop
+  then       is steep
+  ( y0 y1 x0 x1 )
+  2dup >
+  if swap 2swap swap  \ ensure x1 > x0
+  else    2swap
+  then
+  ( x0 x1 y0 y1 )
+  2dup >
+  if   ['] 1-
+  else ['] 1+
+  then is ystep
+  over - abs    { y deltay }
+  swap 2dup - dup { deltax }
+  2/ rot 1+ rot
+  ( error x1+1 x0 )
+  do  color i y steep bmp b!
+      deltay -
+      dup 0<
+      if   y ystep to y
+           deltax +
+      then
+  loop
+  drop ;
+
+5 5 bitmap value test
+0 test bfill
+1 0 4 1 red test line
+4 1 3 4 red test line
+3 4 0 3 red test line
+0 3 1 0 red test line
+test bshow cr
+ **
+ * **
+*   *
+** *
+  **
+ok