Bitmaps and Turtles

Bitmaps are a fundamental part of Logo. A bitmap represents a moveable image on the graphics canvas. Bitmaps can be rotated, stretched, and moved around. A turtle is just a special bitmap that can draw.

These commands handle the number of turtles, how they are created, and how to talk to them.

ARC

Draws an arc; expects between two inputs and three inputs, but parentheses are needed if not called with two inputs.

Syntax

ARC degrees radius
(ARC degrees radius TRUE)

Description

ARC draws an arc, which is part of a circle. The center is the position of the turtle. The arc is drawn with the given radius. It starts at the current heading of the turtle and continues clockwise for the given number of degrees if degrees is positive, or counterclockwise if degrees is negative. The turtle does not move.

If you use TRUE as the third input to ARC, Logo closes the arc by drawing a line from endpoint to endpoint.

Examples

REPEAT 12 [ARC 15 60 RT 30]

BACK

Also: BK

Moves a turtle backwards; one input.

Syntax

BACK number

Description

BACK moves the turtle in the opposite direction of its HEADING by the distance specified by its input. See also FORWARD.

The BACK command works slightly differently for a Blue-Bot robot controlled by Logo via Bluetooth. Blue-Bot moves in fixed-size units. A value of 1 does not mean a single pixel as the screen turtle, but one Blue-Bot movement unit, which is about 6 inches (15 cm). If you, for example, use the command BACK 2, Blue-Bot will move backward one unit, stop briefly, and then move backward a second unit.

For screen widgets, BACK multiplies its input with the turtle’s WIDGET/STEPSIZE property. Setting the WIDGET/STEPSIZE property to, for example 15 (for a Blue-Bot turtle on screen), a turtle would move 15 pixels for each BACK unit.

Examples

BACK 50 BK 50

CTURTLES

Arranges turtles in a circle; one input.

Syntax

CTURTLES number

Description

CTURTLES activates and makes visible the number of turtles specified by its input and arranges them in a circle in the center of the Graphics window.

CTURTLES creates a new set of turtles using the SETTURTLES command.

Examples

DRAW CTURTLES 10 FD 40

DISTANCE

Reports the distance between the turtle and a location; expects between one input and two inputs, but parentheses are needed if not called with one input.

Syntax

DISTANCE [x y]
(DISTANCE x y)

Description

DISTANCE reports a number which is the distance in turtle steps from the first active turtle to the specified point. DISTANCE can be used to test how close a turtle is to another turtle, the mouse, or a target.

Examples

ASK 1 [SETPOS [50 50] SHOWTURTLE] ASK 2 [SETPOS [0 50] SHOWTURTLE] DISTANCE ASK 1 [POS] Result: 70.71 DISTANCE ASK 2 [POS] Result: 50

DOT

Draws a dot; expects between zero inputs and two inputs, but parentheses are needed if not called with one input.

Syntax

DOT [xcoordinate ycoordinate]
(DOT xcoordinate ycoordinate)
(DOT)

Description

DOT draws a dot at the specified location. When DOT has no input and is enclosed in parentheses, it draws a pixel at the location of the turtle. When Logo draws a single pixel, it ignores the PENERASE and PENREVERSE modes of the pen; it simply draws the pixel.

DOT draws a dot for each active turtle. If coordinates are given, the coordinates are relative to the origin and scale of each active turtle. The dot is as wide as the pen width set with SETWIDTH.

Examples

TO RANDOM.DOTS :COUNT :AREA REPEAT :COUNT [DOT SENTENCE RANDOM :AREA RANDOM :AREA] END RANDOM.DOTS defined SETPC “RED RANDOM.DOTS 300 50

DOT?

Also: DOTP

Tests whether a pixel is present at the given location; expects between zero inputs and two inputs, but parentheses are needed if not called with any inputs.

Syntax

DOT?
(DOT? [xcoordinate ycoordinate])
(DOT? xcoordinate ycoordinate)

Description

DOT? reports TRUE if the pixel identified by its argument has a color that is not fully transparent. The coordinates are the coordinates of the first active turtle. If DOT? is called with a coordinate pair as input (enclosed in parentheses), it uses the given coordinates relative to the origin and scale of the first active turtle.

Note that the background color or image is not part of a drawing, and its color at the given coordinates cannot be examined. If nothing has been drawn at the given location, the color that DOTCOLOR reports would be [0 0 0 0], which is invisible black.

Examples

DOT [50 50] (DOT? [50 50]) Result: TRUE

DOTCOLOR

Reports the color of a pixel; expects between zero inputs and two inputs, but parentheses are needed if not called with one input.

Syntax

DOTCOLOR [xcoordinate ycoordinate]
(DOTCOLOR xcoordinate ycoordinate)
(DOTCOLOR)

Description

DOTCOLOR reports the color of the pixel identified by its argument. The color is reported as a list of Red, Green, Blue and Alpha values. When DOTCOLOR has no input and is enclosed in parentheses, it reports the color of the pixel under the first active turtle. If coordinates are used as input, the coordinates are screen coordinates, with [0 0] at the center.

If the alpha value of the color is 0, the dot is invisible, and the background is visible at that position. Note that the background color or image is not part of a drawing, and its color at the given coordinates cannot be examined. Hence, DOTCOLOR reports the color of a location that has not been drawn onto as [0 0 0 0], which is a fully transparent (invisible) black.

Note that if you draw with a small line width, you may receive a different color than expected, because the drawing algorithm tries to smooth the line by adding or using pixels that do not have the exact same color or alpha value that you used to draw.

EDSHAPE

Launches the shape editor; no inputs.

Syntax

EDSHAPE

Description

Launches the shape editor. For a detailed description, please see the Logo Manual.

FILL

Fills an area; expects between zero inputs and one input, but parentheses are needed if not called with any inputs.

Syntax

FILL
(FILL tolerance)

Description

FILL fills an area of the Graphics panel with the current turtle color; it does not use the current pattern set with the SETPATTERN command. FILL picks up the color at the current turtle position and stops at a closed border of any other color. If the turtle’s pen state is not PENDOWN, FILL does nothing.

Logo supports transparent colors. To make Logo fill transparent colors, FILL accepts a second, optional input. This is a tolerance value between 0 and 1 that affects the way Logo fills transparent colors. A value of 0 makes FILL stop at any color regardless of its transparency, while a value of 1 fills any color, resulting in a complete fill of the entire area. As a default value, Logo uses the value 0.5, which fills all colors that are more than half-transparent.

A clean Graphics panel does not contain any color at all (it is actually pre-filled with a totally transparent black color). When drawing, Logo uses anti-aliasing, which results in smoother lines. Logo does this by adding semi-transparent pixels to the line to create the impression of a smooth line. By using a tolerance value of 0.5, FILL fills these semi-transparent values up to the “real” line. Try, for example, to fill a circle with a tolerance value of 0 to see slight remains of white-looking pixels that Logo refused to fill.

Also, if you fill a colored area with another color, Logo will happily fill the entire screen because it does not stop at the boundary where the initial no-color area begins because of the too-high default tolerance value of 0.5. In this case, (FILL 0) (fill with zero tolerance) also works just fine. Consider this example:

DRAW

; create a filled rectangle

(STAMPRECT 100 100 TRUE)

; move the turtle to the center of the rectangle and fill

PU SETXY [50 50] PD SETPC "RED FILL

This will fill the entire screen, because the starting point is the center of the rectangle (at 50 50). FILL will fill the rectangle, but it won’t stop when it finds a no-color pixel due to the tolerance value. As a result, the entire screen turns red.

If you use (FILL 0), FILL will only fill black pixels, stopping correctly at the no-color pixels.

FONTS Result: [TIMES HELVETICA COURIER SERIF SANS_SERIF MONOSPACE LUMINARI BRADLEY MONACO VERDANA TAHOMA IMPACT]

FORWARD

Also: FD

Moves a turtle forward; one input.

Syntax

FORWARD number

Description

FORWARD moves the turtle in the direction of its HEADING by the distance specified by its input. See also BACK.

The FORWARD command works slightly differently for a Blue-Bot robot. Blue-Bot moves in fixed-size units. A value of 1 does not mean a single pixel as the screen turtle, but one Blue-Bot movement unit, which is about 6 inches (15 cm). If you, for example, use the command FORWARD 2, Blue-Bot will move forward one unit, stop briefly, and then moves forward a second unit.

For screen widgets, FORWARD multiplies its input with the turtle’s WIDGET/STEPSIZE property. Setting the WIDGET/STEPSIZE property to, for example 15 (for a Blue-Bot turtle on screen), a turtle would move 15 pixels for each FORWARD unit.

Examples

FORWARD 50 FD 50

HEADING

Reports the heading of the first active turtle; no inputs.

Syntax

HEADING

Description

HEADING reports the turtle’s heading, a number between 0 and 360, representing the turtle’s angle from the straight up position. Straight up is 0, to the right is 90, down is 180, and to the left is 270.

Use SETHEADING to set the turtle’s heading.

Examples

TO NAUTILUS RT 10 FORWARD HEADING BACK HEADING IF HEADING < 90 THEN NAUTILUS END NAUTILUS defined NAUTILUS

HIDETURTLE

Also: HT

Hides all active turtles; no inputs.

Syntax

HIDETURTLE

Description

HIDETURTLE makes the turtle shape invisible. To make the turtle visible, use SHOWTURTLE. See also SHOWN?.

HOME

Moves the turtle back to [0 0]; no inputs.

Syntax

HOME

Description

HOME moves the turtle to the center of the screen and points the turtle straight up without clearing the graphics screen or altering the pen state. Typing HOME is equivalent to entering SETXY [0 0] SETHEADING 0.

Examples

DRAW TO HEART REPEAT 10 [FD 5 RT 18] REPEAT 22 [FD 3 RT 3] PU HOME PD REPEAT 10 [FD 5 LT 18] REPEAT 22 [FD 3 LT 3] HT END Result: HEART defined HEART

LEFT

Also: LT

Turns a turtle left; one input.

Syntax

LEFT number

Description

LEFT rotates the turtle left (counterclockwise) the number of degrees specified in its input.

Note that a Blue-Bot robot turns in increments of 45 degrees, and an InO-Bot robot turns in increments of 5 degrees. Therefore, the input to LEFT must be a multiple of 45 for Blue-Bot and 5 for InO-Bot. InO-Bot only accepts input values between -180 and 180.

Examples

LEFT 45

LOADSHAPE

Loads a turtle shape from a file and sets the shape of all active turtles; expects between zero inputs and one input, but parentheses are needed if not called with one input.

Syntax

LOADSHAPE filename
LOADSHAPE [extensions-list]
(LOADSHAPE)

Description

LOADSHAPE loads the specified image and sets the shape of all active turtles to that image. If you use LOADSHAPE without inputs, LOADSHAPE opens a dialog box that lets you select a shape to load.

If you use LOADSHAPE without inputs, Logo displays a dialog that lets you select a file name.

If you use a file name instead of a path name and the file was not found, Logo tries to load that file from the “Shapes” toolbox folder. The command LOADSHAPE “~5 would, for example, first try to load the file “~5.png” from the current folder, and then try to load the file from “~HOME/TOOLBOX/SHAPES/~5.PNG”. This is a convenience function that saves you from having to enter a full path when you want to load a file from the “Shapes” folder.

LOADSNAP

Loads a bitmap; expects between zero inputs and one input, but parentheses are needed if not called with one input.

Syntax

LOADSNAP filename
LOADSNAP [extensions-list]
(LOADSNAP)

Description

LOADSNAP loads the specified file into a newly created BITMAP widget. LOADSNAP can load various bitmap formats. If no extension is given to the filename, the picture format that is attempted to be loaded is the format specified in the göobal variable :PICTURE.FORMAT. If the file has a different extension, then the extension must be specified in the LOADSNAP command. LOADSNAP reports the name of the created widget. This result can be used as the input to SNAP or STAMP, or added to the TELL list.

If you use the command without inputs, Logo displays a dialog that lets you select a file name.

Examples

LOADSNAP “~HOME/TOOLBOX/ANIMALS/BEE Result: BITMAP.1

LTURTLES

Arranges turtles in a row; expects between one input and two inputs, but parentheses are needed if not called with one input.

Syntax

LTURTLES number
(LTURTLES number distance)

Description

LTURTLES activates and makes visible the number of turtles specified by its input and arranges them in a horizontal line along the center of the Graphics window. An optional second input specifies the distance in pixels between each turtle, which must be zero or greater. The default distance is 14 pixels.

LTURTLES creates a new set of turtles using the SETTURTLES command.

Examples

DRAW LTURTLES 15 FD 100

OPACITY

Reports the opacity of the first active turtle; no inputs.

Syntax

OPACITY

PENDOWN

Also: PD

Puts the pen down; no inputs.

Syntax

PENDOWN

Description

PENDOWN puts the turtle’s pen down and causes the turtle to draw a line when it moves. Used in conjunction with PENUP. DRAW puts the pen down. See also PENDOWN?, SETPEN, PENUP, PENERASE, and PENREVERSE.

PENDOWN?

Also: PENDOWNP

Checks whether the pen is down; no inputs.

Syntax

PENDOWN?

Description

PENDOWN? reports TRUE if the pen of the current turtle is in a drawing mode. Thus, it reports TRUE if the pen is set to PENDOWN, PENERASE, or PENREVERSE mode, where the turtle may affect the graphics when it moves. When the pen is set to PENUP mode, PENDOWN? reports FALSE.

Examples

PENDOWN PENDOWN? Result: TRUE PENUP PENDOWN? Result: FALSE PENERASE PENDOWN? Result: FALSE

PENERASE

Also: PE

The pen draws with the background color; no inputs.

Syntax

PENERASE

Description

PENERASE turns the turtle’s pen into an eraser. When the turtle moves, it appears to erase by drawing in the current background color.

Note that PENERASE may leave some residue behind due to an effect called anti-aliasing.

See also PENDOWN, PENUP, PENREVERSE, or SETPEN.

PENREVERSE

Also: PX

The pen inverts all colors; no inputs.

Syntax

PENREVERSE

Description

PENREVERSE inverts the drawing. It erases anything drawn, and draws if there is no drawing.

Note that PENREVERSE may leave some residue behind due to an effect called anti-aliasing.

See also SETPEN, PENDOWN, PENUP, and PENERASE.

PENUP

Also: PU

The pen moves up; no inputs.

Syntax

PENUP

Description

PENUP puts the turtle’s pen up. When the turtle moves, it does not draw a line. Used in conjunction with PENDOWN. See also PENDOWN?, PENERASE, and PENREVERSE.

PHEADING

Reports the turtle’s polar heading; no inputs.

Syntax

PHEADING

Description

PHEADING reports the polar heading of the turtle. A heading of 0 degrees is equivalent to a Cartesian heading of 90 degrees. Set the polar heading with PSETHEADING.

Examples

SETP 35 60 PSETH 180 PHEADING Result: 180

POS

Also: GETXY

Reports the coordinates of a turtle; no inputs.

Syntax

GETXY

Description

GETXY reports a list consisting of the x and y coordinates of the turtle. GETXY is equivalent to POS. See also GETX, GETY, SETX, SETY, and SETXY.

Examples

GETXY Result: [0 0]

PPOS

Reports the turtle’s polar position; no inputs.

Syntax

PPOS

Description

PPOS reports the turtle’s polar position, a list of two numbers: the distance from home and the polar angle. Set the polar position using SETP. Polar coordinates describe positions on a plane in terms of the distance from the turtle’s home in the center of the Graphics panel and the angle from 0 degrees. Polar coordinates measure degrees counterclockwise from a 0 degree heading equivalent to 3 o’clock. See also PHEADING, PANGLE, and PDIST.

PSETHEADING

Also: PSETH

Sets the polar heading of a turtle; one input.

Syntax

PSETHEADING number
PSETH number

Description

Polar coordinates describe positions on the plane in terms of the distance from the turtle’s home and the angle from 0 degrees. Polar coordinates measure degrees counterclockwise from a 0 degree heading that is equivalent to 3 o’clock. PSETHEADING sets the polar heading of the turtle. A polar heading of 0 degrees is equivalent to 90 degrees in the turtle’s normal (Cartesian) coordinate system. PHEADING reports the polar heading. See also SETP, PPOS, PANGLE, and PDIST.

Examples

SETP 35 60 PSETH 180 PHEADING Result: 180

RIGHT

Also: RT

Turns a turtle right; one input.

Syntax

RIGHT number

Description

RIGHT rotates the turtle right (clockwise) the number of degrees specified in its input.

Note that a Blue-Bot robot turns in increments of 45 degrees, and an InO-Bot robot turns in increments of 5 degrees. Therefore, the input to RIGHT must be a multiple of 45 for Blue-Bot and 5 for InO-Bot. InO-Bot only accepts input values between -180 and 180.

Examples

RIGHT 45

SAVESHAPE

Saves the shape of the first active turtle; expects between zero inputs and one input, but parentheses are needed if not called with one input.

Syntax

SAVESHAPE filename
SAVESHAPE [extensions-list]
(SAVESHAPE)

Description

SAVESHAPE saves the shape of the first active turtle or bitmap to a data space. The shape is not saved in a rotated or scaled state.

If you use the command without inputs, Logo displays a dialog that lets you select a file name.

SAVESNAP

Saves a turtle shape; expects between zero inputs and two inputs, but parentheses are needed if not called with two inputs.

Syntax

SAVESNAP turtle filename
(SAVESNAP turtle)

Description

SAVESNAP saves a turtle shape as a bitmap file to a file. The shape is not saved in a rotated or scaled state. These images can be loaded with LOADSNAP, LOADSHAPE or LOADPIC.

SAVESNAP is used to save a bitmap shape that a previous SNAP command has created. It is very similar to the SAVESHAPE command, which saves the shape of the first active turtle.

If you omit the second input, Logo displays a dialog that lets you select a file name.

SETFONT

Sets the turtle drawing font; expects between zero inputs and three inputs, but parentheses are needed if not called with three inputs.

Syntax

SETFONT name size attributes
(SETFONT name size)
(SETFONT name)
(SETFONT)
(SETFONT [name size attributes])
(SETFONT [name size])
(SETFONT [name])
(SETFONT [])

Description

SETFONT defines the turtle font. The first input is the font name. This font should be present in the system. If the font is not present, the operating system selects a similar font for you. The second input is the font size, given in points, while the third is one of the following values:

Value	Effect	Value	Effect
0	regular	2	italics
1	bold	3	bold italics

SETFONT can also be called with fewer than three inputs; in that case, the parts of the font that are not supplied are left unchanged. Calling SETFONT with no inputs causes the font to be reset to the default turtle font. Also, calling SETFONT with a list of zero to three elements makes it possible to match the output of FONT with the input to SETFONT. See also FONT, FONTS and TURTLETEXT.

Examples

SETFONT “TIMES 24 1 TT “HELLO

SETHEADING

Also: SETH

Sets the heading of a turtle; one input.

Syntax

SETHEADING number

Description

SETHEADING turns the turtle to the degree position specified by its input. Positive numbers turn the turtle clockwise.

SETHEADING turns the turtle relative to zero degrees and not the current heading of the turtle. SETHEADING 0 always points the turtle straight up, regardless of the direction in which it is pointing.

To output the turtle’s heading, use HEADING.

Please note that changing the heading makes the bounding box increase and decrease according to the angle.

Examples

TO NAUTILUS RT 10 FORWARD HEADING BACK HEADING IF HEADING < 90 THEN NAUTILUS END Result: NAUTILUS defined NAUTILUS

SETOPACITY

Sets the opacity of all active turtles; one input.

Syntax

SETOPACITY value

Description

The SETOPACITY command sets the opacity value of all active turtles. This is a value between 0 (totally transparent, so they are invisible) and 1 (totally opaque). Setting a value lower than 1 makes the drawing, other widgets beneath the turtles, or the background shine through. See also OPACITY.

Examples

TELL 0 SETOPACITY 0.5 SETTS 2 TELL 1 ST SETTS 2 PU RT 90 FD 60 LT 90 PD SETOPACITY 0.8

SETORIGIN

Sets the coordinate system origin of the active turtles; expects between zero inputs and one input, but parentheses are needed if not called with one input.

Syntax

SETORIGIN [x y]
(SETORIGIN x y)
(SETORIGIN)

Description

The SETORIGIN command allows the coordinate system origin point to be set for active turtles. Normally, the coordinate system origin (location [0 0]) is at the center of the canvas. This origin may be changed for all turtles or individually for any turtle.

The input for SETORIGIN is a list of two integers, an X value and a Y value. The coordinates are always relative to the standard turtle coordinate system, where [0 0] is the center of the canvas. If you supply a single number, it sets both the X and Y coordinates. (SETORIGIN) resets the origin to the center of the canvas.

Each turtle can have its own origin on the screen.

Examples

ASK 1 [SETXY [25 0] SETORIGIN POS] TELL [0 1] ST HOME PD FD 50 RT 135 FD 36 HOME

SETP

Sets the turtle’s polar position; two inputs.

Syntax

SETP distance angle

Description

SETP sets the turtle’s polar position. It takes two inputs: a distance and a polar angle. It aims the turtle at the specified polar heading and moves it forward the specified distance. Polar coordinates describe positions on a plane in terms of the distance from the turtle’s home in the center of the Graphics panel and the angle from 0 degrees. Polar coordinates measure degrees counterclockwise from a 0 degree heading equivalent to 3 o’clock. See also PHEADING, PANGLE, and PDIST.

Examples

SETP 100 30 Result: **Turtle moves 100 units away from the center with a heading of 60 (= 90 - 30) degrees**

SETPEN

Sets the pen characteristics; one input.

Syntax

SETPEN [penstate pencolor]

Description

SETPEN changes the state of the turtle’s pen and the pen color as specified by its input list. The first element of the list can be PENUP, PENDOWN, PENERASE, or PENREVERSE. The second element is a number from 0 to 138 (the index of a color name that the COLORS procedure returns, a color word or a list of up tp four RGBA values, which specifies the pen color. Use PEN to output the current turtle’s pen state and PENCOLOR to output the current turtle’s pen color. See also SETPC.

Examples

SETPEN [PENDOWN RED] FD 50

SETSHADOW

Sets the drop shadow for all active turtles; one input.

Syntax

SETSHADOW value

Description

The SETSHADOW command sets the drop shadow for all active turtles. This is a value between 0 and 99, and describes the offset in pixels of the drop shadow. The drop shadow simulates a light source towards the upper left corner of the display. A value of 3, for example, creates a neat little shadow underneath the turtle. See also SHADOW.

Examples

(LTURTLES 8 25) EACH [SETSHADOW WHO]

SETSHAPE

Sets the shape of all active turtles; expects between zero inputs and one input, but parentheses are needed if not called with one input.

Syntax

SETSHAPE name-of-shape
(SETSHAPE)

Description

SETSHAPE redefines the shape of the active turtle(s). Its input is the name of a bitmap or turtle holding the shape to assign to the active turtle(s). If SETSHAPE is used with no arguments and enclosed in parentheses, the original turtle shape is restored for all active turtle(s).

If the name of the shape does not refer to another bitmap or turtle, SETSHAPE attempts to load a shape from a file just like LOADSHAPE.

Examples

SETSHAPE “TRAIN

SETSPEED

Sets the speed at which turtle commands are executed; one input.

Syntax

SETSPEED number

Description

SETSPEED determines the speed at which the turtles move on the screen when being issued a movement command. SETSPEED accepts a number from 0.1 to 1 as an input. A speed of 1 is the fastest speed and 0.1 is the slowest. When Logo starts, the turtle speed is 1. SETSPEED slows down the execution speed of any movement command. To retrieve the current speed, use SPEED.

SETSPEED sets the value of the turtle’s WIDGET/CRAWL property.

Examples

SETSPEED 0.5 FD 100 SETSPEED 1

SETSTEPSIZE

Sets the step size of all active turtles and bitmaps; one input.

Syntax

SETSTEPSIZE pixels

Description

SETSTEPSIZE sets the distance, in pixels, that Logo turtles and widgets move with each FORWARD or BACK command. SETSTEPSIZE sets this value for all currently active Logo turtles and widgets. By default, each Logo turtle and widget moves in steps of one pixel.

To obtain the step size for a turtle or widget, use STEPSIZE.

Examples

FD 10 SETSTEPSIZE 10 FD 10 SETSTEPSIZE 1 BK 110

SETTURTLENAME

Also: SETTNAME

Sets the name of a turtle; two inputs.

Syntax

SETTURTLENAME turtle name

Description

SETTURTLENAME sets the alias name of the widget whose object name is supplied as its first input. It also sets the widget’s WIDGET/TOOLTIP property. Note that the new name is an alias to the original name; you can use both the original and the alias name to address the widget.

To get the widget alias name, see TURTLENAME.

Examples

SETTNAME 0 “JOE TNAME Result: JOE

SETVELOCITY

Controls the speed of an independently moving widget; one input.

Syntax

SETVELOCITY number

Description

The SETVELOCITY command controls the speed at which a widget moves on the screen independently. A widget is a bitmap, a turtle, or a control. The input is a number between 0 and 500. Any number other than 0 causes the widget(s) to start moving at the given speed, which is approximately the number of pixels (dots) per second. A value of 0 (which is the default) causes the widget to stop moving.

VELOCITY reports the number of pixels per second that a widget moves independently per second.

SETVELOCITY alters the WIDGET/VELOCITY property of all widgets on the TELL list.

Examples

SETVELOCITY 50

SETWIDTH

Also: SETW

Sets the pen width; one input.

Syntax

SETWIDTH number

Description

SETWIDTH defines the width of the line drawn by all active turtles. SETWIDTH takes a number between 1 and 999 as input. WIDTH reports the current line width. See also PENDOWN, PENREVERSE, and PENERASE.

Examples

SETWIDTH 10 FD 50 SETWIDTH 5 FD 50 SETWIDTH 1 FD 50

SETX

Sets the X coordinate of a turtle; one input.

Syntax

SETX x-coordinate

Description

SETX moves the turtle horizontally to the point specified by the input number. SETX does not affect the turtle’s heading or its Y coordinate. See also SETY, SETXY, GETX, GETY, and GETXY.

Examples

HOME SETX 45

SETXY

Also: SETPOS

Sets the coordinates of a turtle; expects between one input and two inputs, but parentheses are needed if not called with one input.

Syntax

SETXY [x-coordinate y-coordinate]
(SETXY x-coordinate y-coordinate)

Description

SETXY moves the turtle to the point specified by its inputs. SETXY does not affect the turtle’s heading. To obtain the X and Y coordinates of the turtle, use GETXY or the equivalent command, POS. SETXY accepts a two-element list of coordinates or two numeric inputs.

See also SETX, SETY, GETX, GETY, and GETXY.

Examples

HOME SETXY [50 50]

SETY

Sets the Y coordinate of a turtle; one input.

Syntax

SETY y-coordinate

Description

SETY moves the turtle vertically to the point specified by the input number. SETY does not affect the turtle’s heading or its X coordinate. See also SETX, SETXY, GETX, GETY, and GETXY.

Examples

HOME SETY 45

SHADOW

Reports the drop shadow for the first active turtle; no inputs.

Syntax

SHADOW

Description

The SHADOW command reports the drop shadow for the first active turtle. This is a value between 0 and 99, and describes the offset in pixels of the drop shadow. The drop shadow simulates a light source towards the upper left corner of the display. A value of 3, for example, creates a neat little shadow underneath the turtle. The initial value is 0, which means no shadow at all. See also SETSHADOW.

Examples

SHADOW Result: 0

SHAPE

Outputs the name of the first active turtle’s shape; no inputs.

Syntax

SHAPE

Description

SHAPE reports the name of the shape of the current turtle. The name of the turtle’s default shape is the empty name. Use SETSHAPE or LOADSHAPE to alter the shape of a turtle.

Examples

SHAPE Result:

SHOWN?

Also: SHOWNP

Reports whether a turtle is visible; no inputs.

Syntax

SHOWN?

Description

SHOWN? reports TRUE if the first active turtle is currently displayed on the graphics screen; otherwise, it reports FALSE. See also HIDETURTLE and SHOWTURTLE.

SHOWTURTLE

Also: ST

Makes a turtle visible; no inputs.

Syntax

SHOWTURTLE

Description

SHOWTURTLE makes all active turtles visible. To make the turtles invisible, use HIDETURTLE. See also SHOWN?.

SLOWTURTLE

Slows down the turtle to half speed; no inputs.

Syntax

SLOWTURTLE

Description

SLOWTURTLE slows down the execution speed of any movement commend. It is equivalent to the command SETSPEED 0.5. Use SETSPEED 1 to restore the turtle speed.

To retrieve the current speed, use SPEED.

Examples

SLOWTURTLE SPEED Result: 0.5 SETSPEED 1

SPEED

Reports the speed at which turtle commands are executed; no inputs.

Syntax

SPEED

Description

SPEED reports the current speed at which the turtle(s) moves on the screen. When Logo starts, the turtle speed is 1. Values range from 0.1 to 1; the lower the value is, the slower the turtle moves. Use SETSPEED to change the speed.

Examples

SPEED Result: 1

STAMPOVAL

Draws an oval; expects between two inputs and four inputs, but parentheses are needed if not called with two inputs.

Syntax

STAMPOVAL xradius yradius
(STAMPOVAL xradius yradius "TRUE)
(STAMPOVAL xradius yradius "TRUE angle)

Description

STAMPOVAL draws an oval around the current turtle(s). It takes two numbers as inputs. The first input is the oval’s radius in the horizontal direction; the second input is its radius in the vertical direction. STAMPOVAL draws a circle if the two inputs are equal. If STAMPOVAL, its inputs, and the value TRUE are all enclosed in parentheses, the oval drawn is filled with the current pattern in the current pen color. If the turtle’s pen state is PENDOWN, STAMPOVAL colors the area with the current pen color. If the pen state is PENERASE, STAMPOVAL colors the area with the current background color, thus erasing the form. If the pen state is PENREVERSE, STAMPOVAL colors the area with the complement of the current area color; for example, white turns to black, and green to red. If the turtle’s pen state is PENUP, STAMPOVAL has no effect.

The fourth optional input is the angle to use when stamping. If not otherwise specified, a value of 0 is used, which causes the oval to be stamped with the xradius in horizontal and the yradius in vertical direction. If an angle is given, the oval is rotated to the given number of degrees.

To stamp an oval of 50x100 pixels in the heading of the current turtle, for example, use (STAMPOVAL 50 100 FALSE HEADING)

Examples

STAMPOVAL 100 100 (STAMPOVAL 50 50 TRUE)

STAMPRECT

Draws a rectangle; expects between two inputs and four inputs, but parentheses are needed if not called with two inputs.

Syntax

STAMPRECT width height
(STAMPRECT width height "TRUE)
(STAMPRECT width height fill angle)

Description

STAMPRECT draws a rectangle with a width in turtle steps defined by its first input and a height defined by its second input. The rectangle is drawn with the current turtle position in the lower left corner. STAMPRECT draws a square if the two inputs are equal. If STAMPRECT, its inputs, and the value TRUE are all enclosed in parentheses, the rectangle drawn is filled with the current pattern in the current pen color,

If the turtle’s pen state is PENDOWN, STAMPRECT colors the area with the current pen color. If the pen state is PENERASE, STAMPRECT colors the area with the current background color, thus erasing the form. If the pen state is PENREVERSE, STAMPRECT colors the area with the complement of the current area color; for example, white turns to black, and green to red. If the turtle’s pen state is PENUP, STAMPRECT has no effect.

The fourth optional input is the angle to use when stamping. If not otherwise specified, a value of 0 is used, which causes the rectangle to be stamped with the width in the horizontal direction and the height in the vertical direction. If an angle is given, the rectangle is rotated to the given number of degrees.

To draw a rectangle centered around the turtle’s position and with the same angle as the turtle’s heading, use STAMPRECTC.

Examples

SETPC “RED (STAMPRECT 40 60 “TRUE) PU SETX 75 PD SETPC “SILVER (STAMPRECT 40 60 “TRUE) SETPC “BLACK STAMPRECT 40 60

STAMPRECTC

Draws a rectangle centered around the turtle position; expects between two inputs and four inputs, but parentheses are needed if not called with two inputs.

Syntax

STAMPRECTC width height
(STAMPRECTC width height "TRUE)
(STAMPRECTC width height fill angle)

Description

STAMPRECTC draws a rectangle with a width in turtle steps defined by its first input and a height defined by its second input. The rectangle is drawn with the current turtle position centered around the turtle. STAMPRECT draws a square if the two inputs are equal. If STAMPRECTC, its inputs, and the value TRUE are all enclosed in parentheses, the rectangle drawn is filled with the current pattern in the current pen color.

The turtle draws the rectangle in the same angle as its heading if you do not supply an angle as its fourth input.

If the turtle’s pen state is PENDOWN, STAMPRECTC colors the area with the current pen color. If the pen state is PENERASE, STAMPRECTC colors the area with the current background color, thus erasing the form. If the pen state is PENREVERSE, STAMPRECTC colors the area with the complement of the current area color; for example, white turns to black, and green to red. If the turtle’s pen state is PENUP, STAMPRECTC has no effect.

Examples

SETPC “RED (STAMPRECTC 40 60 “TRUE) PU SETX 75 PD SETPC “SILVER (STAMPRECTC 40 60 “TRUE) SETPC “BLACK STAMPRECTC 40 60

STEPSIZE

Outputs the step size of the first active turtle or bitmap; no inputs.

Syntax

STEPSIZE

Description

STEPSIZE outputs the distance, in pixels, that Logo turtles and widgets move with each FORWARD or BACK command, for the first active turtle or widget. By default, each Logo turtle and widget moves in steps of one pixel.

To set the step size, see SETSTEPSIZE.

Examples

FD 10 SETSTEPSIZE 10 FD 10 STEPSIZE

TOWARDS

Reports the angle of a position compared to the turtle position; one input.

Syntax

TOWARDS [xcoordinate ycoordinate]

Description

TOWARDS reports a number that is the heading that will point the turtle to the position specified by its input list. SETHEADING TOWARDS [xcoordinate ycoordinate] heads the turtle in the direction of its input list.

Examples

ST SETH 0 SETH TOWARDS [100 100]

TURTLENAME

Also: TNAME

Gets the name of the first active turtle; no inputs.

Syntax

TURTLENAME

Description

TURTLENAME outputs the name of the first active turtle. This is also the value of its WIDGET/NAME property.

To set the turtle name, see SETTURTLENAME.

Examples

SETTNAME 0 “JOE TNAME Result: JOE

TURTLENAMES

Also: TNAMES

Outputs a list of all turtle names; no inputs.

Syntax

TURTLENAMES

Description

TURTLENAMES outputs a list of the names of all turtles. Note that this list does not output turtle numbers, but names if a turtle has been given an alias name. Use ALLTURTLES to obtain a list of turtle numbers.

Examples

TURTLENAMES Result: [0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 JOE JACK]

TURTLES

Reports the number of turtles; no inputs.

Syntax

TURTLES

Description

The TURTLES command reports the total number of available turtles. Set the number of turtles with SETTURTLES. See also TELLALL, ALLTURTLES, TELLEVEN, and TELLODD.

Examples

TURTLES Result: 16

TURTLESIZE

Also: TSIZE

Reports the scaling factor of a turtle; no inputs.

Syntax

TURTLESIZE

Description

TURTLESIZE reports a number, the scaling factor of the current turtle. A turtle’s scaling factor can be in the range of 0.1 to 99. If the turtle’s scaling factors are different for the width and height, TURTLESIZE reports a two-element list with the scaling factors for the turtle’s width and height.

To set the turtle’s size, use SETTURTLESIZE.

TURTLETEXT

Also: TT

Prints its input on the Graphics panel; expects between one input and two inputs, but parentheses are needed if not called with one input.

Syntax

TURTLETEXT whatToPrint
(TURTLETEXT whatToPrint mode)

Description

TURTLETEXT prints its input (word or list) on the Graphics panel at the position of the current turtle. TURTLETEXT prints in the pen color and font of the current turtle. TURTLETEXT has no effect if the turtle’s pen is up.

TURTLETEXT prints text into a box whose top left corner is at the turtle’s location. If you want to use multiple fonts in one line, this is bad because font sizes vary, and the text is not lined up neatly. Therefore, an optional second input defines where the text should be drawn. There are three possible values:

TOP: The turtle position is the top left of the text box. This is the default.
BOTTOM: The turtle position is the bottom left of the text box.
BASELINE: The turtle draws text with the turtle’s Y coordinate set to the baseline of the text, which is an imaginary line that you would use to write text on. This causes the text to be vertically aligned.

The example below demonstrates the three modes of drawing text.

See also FONT, SETFONT, TURTLETEXTSIZE and FONTS.

Examples

TO TTPRINT :LIST :BASE DRAW.LINE :BASE FOREACH :LIST [ (SETFONT FIRST ?) LMAKE “TEXT BF ? LMAKE “WIDTH FIRST TTSIZE :TEXT PD (TT :TEXT :BASE) PU RT 90 FD :WIDTH LT 90 ] END Result: TTPRINT defined TO DRAW.LINE :BASE LMAKE “Y YCOR SETFONT “ARIAL 14 0 PD SETPC “GREEN RT 90 FD 300 SETH 0 TT :BASE SETPC “BLACK PU SETXY LIST 0 :Y SETH 0 END Result: DRAW.LINE defined DRAW MAKE “LIST [ [[Arial 16] |It ain’t over |] [[TIMES 12] |until the |] [[TIMES 22 3] |Fat |] [[TIMES 22 0] |Lady |] [[TIMES 18] |sings.|] ] PU SETXY [0 100] TTPRINT :LIST “BASELINE PU SETXY [0 70] TTPRINT :LIST “TOP PU SETXY [0 0] TTPRINT :LIST “BOTTOM PU SETY -50

TURTLETEXTSIZE

Also: TTSIZE

Outputs the dimensions of a text drawn with the first listening turtle; one input.

Syntax

TURTLETEXTSIZE "text

Description

The TURTLETEXTSIZE command is convenient if you want to erase the background before drawing a text, or if you want to advance the turtle behind or below the text after drawing a text.

Examples

TTSIZE “HELLO Result: [21 14]

VELOCITY

Reports the speed of an independently moving widget; no inputs.

Syntax

VELOCITY

Description

VELOCITY reports the number of pixels per second that a widget (a bitmap, a turtle, or a control) moves independently per second. Use the SETVELOCITY command to control this speed.

VELOCITY reports the name ot the first active widget’s WIDGET/VELOCITY property.

Examples

VELOCITY Result: 0

WIDTH

Reports the pen width; no inputs.

Syntax

WIDTH

Description

WIDTH reports the pen width of the first active turtle. The pen width can be a number between 1 and 99. The pen width is set using the command SETWIDTH. If more than one turtle is active, the pen width of these turtles may be interrogated with WIDTH and the ASK or EACH command.

Examples

DRAW WIDTH Result: 1 TELL [0 1 2 3 4] SETWIDTH 5 EACH [PRINT WIDTH] Result: 5 5 5 5 5

GETX

Also: XCOR

Reports the X coordinate of a turtle; no inputs.

Syntax

GETX

Description

GETX outputs the X coordinate of the turtle’s position in the Graphics panel. See also GETY, GETXY, SETX, SETY, and SETXY.

Examples

GETX Result: 0

GETY

Also: YCOR

Reports the Y coordinate of a turtle; no inputs.

Syntax

GETY

Description

GETY outputs the Y coordinate of the turtle’s position in the Graphics panel. See also GETY, GETXY, SETX, SETY, and SETXY.

Examples

GETY Result: 0

SETTURTLES

Also: SETT

Creates a range of turtles; one input.

Syntax

SETTURTLES number

Description

SETTURTLES defines the total number of turtles available. Their numbers range from 0 to the input of SETTURTLES minus 1. For example, SETTURTLES 16 will create the turtles [0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15]. By default, Logo starts with 16 turtles defined and turtle 0 activated.

SETTURTLES creates turtles with the following characteristics:

Property	Value
Turtle number	0
Turtle name	TURTLE
Turtle color	0 (black)
Turtle size	1
Heading	0
Line width	1
Visible	FALSE
Pattern	0
Pen state	PENUP
Font	Default system font, 9 points

Please note that turtle #0’s pen is down (PENDOWN), and it is visible. Turtle 0 is the only one that is activated (see TELL).

SETTURTLES accepts a number between 1 and 1000 as input. The actual maximum of turtles depends on the speed of the computer. The more turtles you set, the slower turtle movements become.

TURTLES reports the number of turtles that have been defined with SETTURTLES. Use the TELL, ASK, EACH, and WHO commands to access multiple turtles.

Examples

SETTURTLES 4 TURTLES Result: 4

LOCKSHAPE

Prevents a bitmap from turning; no inputs.

Syntax

LOCKSHAPE

Description

LOCKSHAPE prevents the shapes for all active turtles and bitmaps from rotating when the widget turns. This can be convenient when you want the shape to appear in its current orientation and size, regardless of how you turn the turtle or bitmap.

The command HEADING always reports the true heading of the widget. Use UNLOCKSHAPE to restore the shape’s visual orientation to match its heading.

Examples

DRAW SETSPEED .8 SETH 45 FD 100 LOCKSHAPE RT 90 WAIT 500 UNLOCKSHAPE

SETTURTLESIZE

Also: SETTSIZE, SETTS

Sets the scaling factor of a bitmap; expects between one input and two inputs, but parentheses are needed if not called with one input.

Syntax

SETTURTLESIZE number
SETTURTLESIZE [x-scale y-scale]
(SETTURTLESIZE x-scale y-scale)

Description

SETTURTLESIZE sets the scaling factor of the bitmap. The input number(s) must be in the range of -99 to 99, where 0.01 indicates an almost invisibly small bitmap, and 99 the largest possible bitmap. As the size of the turtle increases, its shape becomes more jagged. If SETTURTLESIZE is used with two inputs, or with a two-element list, the first input is the horizontal scaling factor, and the second input is the vertical scaling factor.

If a value is negative, it causes the shape to flip either horizontally, vertically, or both. Examples:

(SETTURTLESIZE -1 1) flips horizontally at a size of 1.

(SETTURTLESIZE 1 -1) flips vertically at a size of 1.

(SETTURTLESIZE -0.5 0.5) makes the turtle half the size and flips it horizontally.

(SETTURTLESIZE 1 5) Creates a long turtle that has 5 times the height as usual.

SETTURTLESIZE 2 is the same as (SETTURTLESIZE 2 2) or SETTURTLESIZE [2 2].

The command TURTLESIZE reports the size of the first bitmap of the TELL list.

Please note that changing the scaling factor does not change the bitmap’s real size. It only scales the bitmap.

Note that turtles also are bitmaps.

Examples

TELL [0 1 2] ST EACH [PU SETX 100 * WHO SETTURTLESIZE WHO + 1]

UNLOCKSHAPE

Lets a bitmap rotate according to the turtle’s heading; no inputs.

Syntax

UNLOCKSHAPE

Description

UNLOCKSHAPE restores the normal rotation of the bitmap, cancelling the effects of LOCKSHAPE. The bitmap immediately returns to the orientation that most accurately represents its true heading.

Examples

DRAW SETSPEED .8 SETH 45 FD 100 LOCKSHAPE RT 90 WAIT 500 UNLOCKSHAPE