turtle.md

Using Sketcher with turtle style graphics.

#TODO: ( code modified you now pass sketcher to a new Turtle instance ) but theory below is very similar.

demo project: https://github.com/nanjizal/cornerContourWebGLTurtle

Sometimes it can be easier to draw using simple turtle graphics. Turtle style graphics allows you to define drawing as if your controlling a turtle, with rotation and movement commands, these commands can be chained together as a sequence:

public function turtleTest(){
       var s = new Sketcher( pen2D, Fine, both );
        s.setPosition( 100, 100 )
            .penSize( 7 )
            .forward( 30 )
            .right( 45 )
            .forward( 30 )
            .arc( 50, 120 );
 }

Specific turtle related commands provided from Sketcher class, these are designed to be easily chained. There is a simple repeat that allows non nested multiple repeat of commands.

Turtle allow draw and move commands.

• penUp() or penup() or up()
• penDown() or pendown() or down()
• movePen( x, y );

s.penUp();
s.penDow();
s.movePen(100,100);

Change angle of pen, internally it works in radians for commands degrees are used for simplicity

• left( degrees ) or lt( degrees )
• right( degrees ) or turn( degrees ) or rt( degrees )
• north()
• south()
• east()
• west()
• setAngle( degrees )

s.left( 45 );
s.right( 45 );
s.north();
s.south();
s.east();
s.west();
s.setAngle( 90 )

Distance movement

• forward( distance ) or fd( distance )
• backward( distance ) or bk( distance )
• setPosition( x, y ) or goto( x, y ) or setposition( x, y ) does not draw.

s.forward( 100 );
s.backward( 100 );
s.setPosition( 300, 300 );

Basic shapes

• circle( radius ) normally draws 24 sides, but you can specify different number in second argument
• arc( radius, degrees ) normally draws 24 sides, but you can specify different number in second argument

s.circle( 100 );
var square = 4; // untested
s.circle( 100, square );
s.arc( 100, 45 );// quarter pie

Basic repeat

• repeatBegin( repeatCount ) or loop( repeatCount ) or repeat( repeatCount )
• endRepeat() or loopEnd() or repeatEnd()

// pentagram or star?
s.repeatBegin( 7 ).forward( 300 ).right( 144 ).endRepeat();

Forward additions for use in loops

• forwardChange( deltaDistance ) ie +=
• forwardFactor( factor ) ie *=

// can experiment with forward commands changing size in loop iteration
s.forward(300).right(144).repeatBegin( 6 ).forwardChange( -10 ).right( 144 ).endRepeat();

Curved Distance, similar to forward, but uses 'distance2' and 'radius' to define a third point relative to the current vector.

• archBezier( distance, distance2, radius ) ends up same place as forward but arches using quad bezier
• triangleArch( distance, distance2, radius ) ends up same place as forward but triangles from the line

Pen thickness and color

• penSize( width ) or pensize( width )
• penColor( r, g, b ) or pencolor( r, g, b )
• penColorChange( r, g, b )

s.penSize( 50 ); //very thick line
s.penColor( 1, 0, 0 ); // red pen
s.circle( 100 );

Default colors are defined similar to other turtle implementations

• black()
• blue()
• green()
• cyan()
• red()
• magenta()
• yellow()
• white()
• brown()
• lightBrown()
• darkGreen()
• darkishBlue()
• tan()
• plum()
• grey()

s.plum(); // plum colored circle
s.circle();

For thickness gradients when using SketcherGrad, untested, second color defaults to 'colorB'

• penColorB( r, g, b )
• penColorC( r, g, b )
• penColorChangeB( r, g, b )
• penColorChangeC( r, g, b )

Limited support for fill, mostly useful for filling circle, but limited use with curve / triangle related commands

• fillOn() or fillon()
• fillOff() or filloff()

s.fillOn();
s.circle( 100 ); // dot
s.fillOff();

Non chainable commands just for information

• toRadians( degrees ) converts degrees to radians
• position() provides current position
• heading() provides current angle

History, the commands are stored internally as abstract enum ie Array and as properties Array

• onTurtleHistory = true
• drawHistory( start, end ) // so you can setPosition and setAngle and draw again somewhere else or perhaps save to disc in future.