Authors: Christian Seely, John Clark

Plumbing Graphics Code Written by Lance Williams.

Example running program: runghc lobo_interp lissajous

Description:

Interpret and render Lobo code (modled after turtle graphics, see: https://en.wikipedia.org/wiki/Turtle_graphics) on the screen.

High Level:

Lobo Code --> S-Expression --> Instruction Stream/ Jump Table --> Graphics Instruction Stream --> Rendered on Screen using Plumbing Graphics.

Lobo Code --> S-Expression

The lobo code defined in a string is read in and converted to an S-Expression data type.

S-Expression --> Instruction Stream/ Jump Table

Next the S-Expression is parsed to produce a jump table and a custom instruction stream. The instructions in the instruction stream are defined in our custom data type, Instruction.

Instruction Stream/ Jump Table --> Graphics Instruction Stream

Next using the instruction stream and jump table constructed in the previous step, a stream of basic graphics instructions is produced. There are only four different graphics instructions produced during this phase of compilation:

Straight GLfloat (Line of GLfloat in length)
Invisible GLfloat (Invisible line of GLfloat in length)
Bend GLfloat (Change the angle pen is facing)
Paint Colour Graphic (Change the color of pen)

All variable resolution is done at this stage in addition to function, arithmetic, and conditional evaluations.

Graphics Instruction Stream --> Rendered on Screen using Plumbing Graphics

Finally the graphics instruction stream is converted into a single recursive instance of the graphics data structure using foldr1. After that the graphics instruction is send to Lance Williams rendering code and rendered to the screen.

Examples:

(define lissajous'
((to lissajous (a b c t)
  (penup)
  (setxy (* (cos c) 75) 100)
  (pendown)
  (repeat 364 
    (color t)
    (setxy (* (cos (+ (* t a) c)) 75) (+ (* (sin (* t b)) 75) 100))
    (make t (+ t 1))))
(lissajous 0.1396 -0.12215 0.2094 0)))"

(define hilbert'
((to hilbert (size level parity)
(if (> level 0)
  ((left (* parity 90))
  (hilbert size (- level 1) (- parity))
  (forward size)
  (right (* parity 90))
  (hilbert size (- level 1) parity)
  (forward size)
  (hilbert size (- level 1) parity)
  (right (* parity 90))
  (forward size)
  (hilbert size (- level 1) (- parity))
  (left (* parity 90)))))
(hilbert 10 4 1)))"

(define tree'
((to tree (depth count)
  (forward (* depth 20))
  (right 90)
  (if (> depth 1)
    (repeat 5 
      (push)
      (left (* count 30))
      (color (* 60 count)) 
  (tree (- depth 1) 1)
  (pop)
  (make count (+ count 1)))))
(tree 4 1)))"

** The following license ONLY applies for code from the stages: S-Expression --> Instruction Stream/ Jump Table --> Graphics Instruction Stream**

**Copyright (C) {2017}  {Christian Seely and John Clark} <[email protected]>**

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.