Directions Programming
Geometry With Turtle Graphics
Directions
For directions and specific explanations, see the following: Turtle Applet Directons and Explanations
Link to Poseidon Software and Invention Home Page
Brief Command and Variable summary.
| Turtle Commands | Syntax | Function |
| CLS | One word command | Clears the screen of drawn graphics |
| RESET | One word command | Resets the modifiable variables (not a generic turtle command, but a good practice to put this at the start) |
| PENUP | One word command | Lifts the pen, so moving will not draw a line |
| PENDOWN | One word command | Readys pen to draw, so moving will draw a line |
| FORWARD | Optional number can follow. If no number follows, the value in LENGTH is used for distance of move. | Moves the turtle in the direction facing. |
| REPEAT | One word command | Repeats the whole script from the start. |
| COLOR | Specific color follows or RANDOM which selects a color | Sets color of pen |
| LEFT | Number follows indicating degress to turn left. | Turns turtle left specific number of degrees. |
| RIGHT | Number follows indicating degrees to turn right. | Turns turtle right specific number of degrees. |
| ERASE | One word command | Erases last entered command (not a generic turtle command. Use when entering commands one at a time and a mistake is made) |
| Variables | Syntax (all variables have same syntax) | Funtions |
| X | = sign followed by number or RANDOM | X coordinate of the turtle |
| Y | see above | Y coordinate of the turtle |
| ANGLE | see above | Positions the direction of the turtle |
| LENGTH | see above | Indicates length of the next move FORWARD if the FORWARD command does not specify a length |
| I | see above | Variable used to store a number |
| J | see above | Variable used to store a number |
| K | see above | Variable used to store a number |
| DELTALENGTH | see above | Indicates how much LENGTH variable will be changed after a move FORWARD |
| DELTAANGLE | see above | Indicates how much ANGLE variable will be changed after a move FORWARD |
| LOWRANDOM | see above | Used to determine low bounds of number that RANDOM generates |
| HIGHRANDOM | see above | Used to determine high bounds of number that RANDOM generatesr |
| XMIN | Read only variable (used only in conditionals) | Represents minimum x coordinate of applet |
| XMAX | Read only variable (used only in conditionals) | Represents maximum x coordinate of applet |
| YMIN | Read only variable (used only in conditionals) | Represents minimum y coordinate of applet |
| YMAX | Read only variable (used only in conditionals) | Represents maximum y coordinate of applet |
| Flow | Syntax | Function |
| DO | One word | Indicates beginning of a DO UNTIL loop. |
| UNTIL | Followed by condition that will end the DO loop. Variable (or number) then the Conditional followed by a variable (or number). Eg. UNTIL I >= 10. or UNTIL ANGLE < 360. Parentheses are optional, eg UNTIL ( I > 10 ) | Indicates the end of a DO UNTIL loop. When the UNTIL statement is reached, the condition is evaluated and if it passes evaluation, the next line is read, otherwise flow goes back to the DO statement preceeding the UNTIL. These loops may be nested. |
| BREAK | One word | Breaks out of a DO UNTIL loop. Instruction processing continues after the UNTIL statement of a DO UNTIL loop. |
| IF | Followed by condition that will to test. Variable (or number), then the Conditional followed by a variable (or number). Eg. IF X >= 200, or IF DELTALENGTH > 50. Parentheses are optional, eg IF ( Y < 20 ) | Indicates the beginning of an IF ENDIF block of instructions. If the condition passes evaluation, then the instructions between the IF and ENDIF statement are carried out. Otherwise nothing happens until the ENDIF statement is reached. |
| ENDIF | One word. | Indicates the end of the IF block of instructions |
| Conditionals | Syntax (occurs in IF or UNTIL statements) | Functon |
| Is equal to | == eg. IF X == 5 or UNTIL x == 5 | Evaluates variable before and after for equality |
| Is greater than | > eg. IF ANGLE > 360 or UNTIL ANGLE > 360 | Tests if variable before is greater than variable after |
| Is less than | < eg. IF DELTALENGTH < -50 or UNTIL DELTALENGTH < -50 | Tests if variable before is less than variable (or number) after |
| Is greater than or equal to | >= eg. IF 5 >= DELTAANGLE or UNTIL 5 >= DELTAANGLE | Tests if variable before is greater than or equal to variable (or number) after |
| Is less than or equal to | <= eg. IF J <= 10 or UNTIL J <= 10 | Tests if variable before is less than or equal to variable (or number) after |
| Operations | Syntax (operates on variables listed above) | Function |
| Sets a variable | = eg. X = 5 | Sets a variable to a number |
| Adds to a variable | += eg. ANGLE += 10 | Adds variable (or number) following to variable before |
| Multiplies a variable | *= eg. LENGTH *= 5 | Multiplies variable (or number) following to variable before |
| Divides a variable | /= eg. LENGTH -= 5 | Divides variable (or number) following from variable before |
| Subtracts from a variable | -= eg. LENGTH -= 5 | Subtracts variable (or number) following to variable before |
| Increments variable | ++ eg.. ANGLE++ | Adds 1 to preceeding variable |
| Decrements variable | -- eg. I-- | Subtracts 1 from preceeding variable |
| More Commands | Syntax | Function |
| DRAW | Followed by 2 arguments with parentheses with comma's or whitespace seperating arguments eg. DRAW(10,10) | Draws a line from the current position to the (X,Y) coordinate given. |
| SETXY | Followed by 2 arguments with parentheses with comma's or whitespace seperating arguments eg. SETXY(10,10) | Positions the turtle at the (X,U) coordinate given. |
| SETRANDOM | Followed by 2 arguments with parentheses with comma's or whitespace seperating arguments eg. SETRANDOM(1,10) | Sets the LOWRANDOM and HIGHRANDOM values to determine the range of a number when RANDOM is used |
| DOT | Followed by 2 arguments with parentheses with comma's or whitespace seperating arguments eg. DOT(10,10) | Draws a dot on the screen 1pixel in size at the given X,Y coordinates |
After the above commands have been investigated you can use JavaScript or VBScript to control the turtle. Also to program some of the recursive functions illustrated in 'Turtle Geometry' you will need a robust scripting language like JavaScript or VBScript. The following page has some examples of using JavaScript to control the Turtle Applet TurtleScript
Date last updated 10/11/98
Copyright 1998 Poseidon Software and Invention