StdDraw & Computer Animation

San Skulrattanakulchai

StdDraw was created by Robert Sedgewick to make drawing graphics easy. This library creates an illusion of standard drawing, a concept similar to the standard input, standard output and standard error output that already exist.
The user has a canvas and a pen, and can issue commands to draw geometric shapes on the canvas.
She can ask the canvas to display images from a file, or save an image on the canvas to a file, as long as the file is in JPEG, PNG, or GIF format.
The library also includes facilities for text, color, and animation, along with user interaction via the keyboard and mouse.

The points on the canvas is addessable using a pair of Double numbers (x, y) just like in the Cartesian coordinates system.
Both the x-axis and y-axis range from 0 to 1 by default but can be changed to anything.
The radius of the pen is 0.005 by default but can be changed.
The default pen color is black but can be changed.

To use StdDraw, you need to have the source code StdDraw.java, or class file StdDraw.class, or jar file stdlib.jar in your possession.
You have to tell kotlinc and kotlin about it too. One way is to provide the -classpath or -cp flag when you invoke the commands, like this
```
$ kotlinc -cp .:stdlib.jar sourceFile.kt
$ kotlin -cp .:stdlib.jar SourceFileKt
```
In the above example, you are telling kotlinc and kotlin that the path to search for class files include . (the current directory) and inside the jar file stdlib.jar.

line(x0: Double, y0: Double, x1: Double, y1: Double)—draw line segment joining point (x0,y0) to point (x1,y1)
point(x: Double, y: Double)—draw the point (x,y)
text(x: Double, y: Double, s: String)—draw the String s centered at point (x,y)
circle(x: Double, y: Double, r: Double)—draw circle centered at point (x,y), with radius r
filledCircle(x: Double, y: Double, r: Double)—draw filled circle centered at point (x,y), with radius r
ellipse(x: Double, y: Double, semiMajorAxis: Double, semiMinorAxis: Double)—draws an ellipse with the specified semimajor and semiminor axes, centered at point (x, y)
filledEllipse(x: Double, y: Double, semiMajorAxis: Double, semiMinorAxis: Double)—draws a filled ellipse with the specified semimajor and semiminor axes, centered at point (x, y)

arc(x: Double, y: Double, radius: Double, angle1: Double, angle2: Double)—draws a circular arc of the specified radius, centered at point (x, y), from angle1 to angle2 (in degrees)
rectangle(x: Double, y: Double, halfWidth: Double, halfHeight: Double)—draws a rectangle of the specified size, centered at point (x, y)
filledRectangle(x: Double, y: Double, halfWidth: Double, halfHeight: Double)—draws a filled rectangle of the specified size, centered at point (x, y).
square(x: Double, y: Double, r: Double)—draw r x r square centered at point (x,y)
fillededSquare(x: Double, y: Double, r: Double)—draw r x r filled square centered at point (x,y)
polygon(x: DoubleArray, y: DoubleArray)—draw polygon
fillededPolygon(x: DoubleArray, y: DoubleArray)—draw filled polygon
picture(x: Double, y: Double, filename: String)—draw specified image centered at point (x,y)
save(filename: String)—save image to specified filename

Signature	Purpose
`setScale()`	sets x-scale and y-scale to default (between 0.0 and 1.0)
`setScale(min: Double, max: Double)`	reset both x-range and y-range to (`min`, `max`)
`setXscale(xmin: Double, xmax: Double)`	reset x-range to (`xmin`, `xmax`)
`setYscale(ymin: Double, ymax: Double)`	reset y-range to (`ymin`, `ymax`)
`clear()`	clears the screen to default color (white)
`clear(color: java.awt.Color)`	clears the screen to specified color
`enableDoubleBuffering()`	enable double buffering
`disableDoubleBuffering()`	disable double buffering

Signature	Purpose
`setPenColor()`	sets pen color to default color (black)
`setPenColor(color: java.awt.Color)`	sets pen color to specified `color`
`setPenRadius()`	sets pen radius to default size (0.002)
`setPenRadius(radius: Double)`	sets pen radius to spedified `radius`
`pause(t: Int)`	pause for `t` milliseconds
`show()`	copies offscreen buffer to onscreen buffer

Motion picture is an illusion that is created by showing a sequence of still images (called “frames”) whose successive images differ by small amount.
As long as the number of frames shown per second is large enough the brain will see a smooth motion.
Double buffering is a technique of using two canvases. It makes the animation feel smooth.
One canvas is shown on the computer screen, while the drawing commands can be issued to the offscreen canvas.
When the offscreen drawing is finished, the canvases are switched.