IAT 334 Java using Processing ______________________________________________________________________________________ SCHOOL OF INTERACTIVE ARTS + TECHNOLOGY [SIAT] |

Processing Processing is built on top of Java Supports script-like coding – Easy to get simple programs up fast – But allows transition to full Java programming Has built-in methods and classes to make drawing easy Easy to export program to applet May 21, 2010IAT 3342

Playing around To learn how to program it is necessary to play around with code!!! – Don’t just wait for me to show you things Processing makes this easy – Use the Reference in the Help menu – or – Play with the examples May 21, 2010IAT 3343

Saving your work You should install Processing on your own machine – Do this immediately Processing saves all projects in a directory you can select via preferences – You should always copy your code to your local disk – Don’t depend on your project remaining undisturbed on lab machines May 21, 2010IAT 3344

Drawing in Processing Automatic creation of display window Window has a coordinate system for drawing May 21, 2010IAT 3345 x y

Let’s draw a point: point() point(x,y) – draws a point at the location x, y Let’s try it: point(50, 50) Unexpected token: null – what ?? Compiler errors appear in the bottom pane All lines must be terminated with a semicolon ; May 21, 2010IAT 3346

Drawing several points point( 30, 20 ); point( 85, 20 ); point( 85, 75 ); point( 30, 75 ); May 21, 2010IAT 3347

Comments Comments are non-program text you put in the file to describe to others (and yourself) what you’re doing Important for being able to look back at your code and understand it Single-line comments begin with // Multi-line comments begin with /* and end with */ Commenting and uncommenting lines is useful for figuring out code May 21, 2010IAT 3348

Drawing shapes: some primitives line(x1, y1, x2, y2); triangle(x1, y1, x2, y2, x3, y3); rect(x, y, width, height); rectMode() – CORNER, CORNERS, CENTER ellipse(x, y, width, height); ellipseMode() – CENTER, CENTER_RADIUS, CORNER, CORNERS Don’t use these draw modes!!! rectMode(), ellipseMode() May 21, 2010IAT 3349

Controlling color and line Colors represented as Red Green Blue (RGB) values Each one ranges from 0 to 255 Can also use Hue Saturation Value (HSV) space, but we won’t worry about this for now background(R,G,B); – set the background color stroke(R,G,B); – set the colors of the outline (default black) noStroke(); – no outline drawing around shapes fill(R,G,B); – set the fill color for shapes (default white) noFill(); – don’t fill the shapes (background shows through) strokeWeight(w); – line width for outlines (default 1) May 21, 2010IAT 33410

Drawing primitives revisited What are the different syntax parts of a drawing primitive? line( 0, 0, 50, 50 ); May 21, 2010IAT method name parentheses contain arguments arguments, parameters

The drawing commands are methods Methods are reusable commands – Like a little machine that does work for you – Let’s you reuse code without typing it over and over The arguments tell the method precisely what to do We’ll see later that you can define your own methods! May 21, 2010IAT 33412

Introduction to variables A variable is a named box for storing a value You can put values in a variable by using the assignment operator (aka “=“ ) e.g. x = 1; To use the value stored in a variable, just use the variable’s name e.g. line(x, 0, 50, 50); May 21, 2010IAT 33413

Variables have a type You must tell Processing (Java) what kinds of values can go in the box You do this by giving a variable a type May 21, 2010IAT int x; // variable x can hold integers (int) int y; // variable y can hold integers (int) x = 20; // store 20 in x y = 30; // store 30 in y point(x, y); // use the values of x and y to draw a point

Effect of creating an int variable May 21, 2010IAT // Single int int anInt; // Put a value in the int anInt = 3; // Type error! anInt = “hello”; CodeEffect Name: anInt, Type: int 3 “hello” Can’t shove “hello” into an int

Assigned values must match the type May 21, 2010IAT int x; // variable x can hold integers (int) int y; // variable y can hold integers (int) x = 1.5; // store 1.5 in x causes an error!!! y = 30; // store 30 in y point(x, y); // use the values of x and y to draw a point

Why Types? Tells system (and you) what kind of values to expect System uses type to detect errors int pi = 3.14 ; //  error: 3.14 not an int May 21, 2010IAT 33417

The “primitive” types int – integers between 2,147,483,648 and 2,147,483,647 float – floating point numbers (e.g , -2.34) char – a single character (e.g. ‘c’) byte – integers between -128 and 127 boolean – holds the values true or false color – holds a color (red, green, blue, alpha) May 21, 2010IAT 33418

Can combine declaring and assigning Declaring a variable means telling Processing its type int x; Assigning a value to a variable means putting a value in the named box x = 1; You can declare and assign at the same time int x = 1; But only declare a variable once, otherwise you get an error May 21, 2010IAT 33419

Print and println When working with variables, it is often convenient to look at their values print() and println() print to the bottom processing pane – They do the same thing, except println starts a new line after printing May 21, 2010IAT 33420

Control flow By default Processing (Java) executes the lines of a method one after the other – Sequential control flow – Unconditional – doesn’t matter what happens in the world Often we want which steps are executed to depend on what else has happened That is, we want conditional control flow – This is necessary in order to make anything that is interactive May 21, 2010IAT 33421

If if statements introduce conditional branches if ( ) { // do this code } have one of two values: true or false May 21, 2010IAT 33422

Some boolean expressions May 21, 2010IAT anInteger == 1 true if variable anInteger is equal to 1 x > 20 true if variable x is greater than 20 1 == 2 true if 1 is equal to 2, it’s not so this is false ! is the not operator – reverses true and false so, ! (1 == 2) is true This is not a boolean expression: int anInteger = 1;

Example Try changing the values of drawRect and drawAnX May 21, 2010IAT strokeWeight(2); // draw with heavier line stroke(200, 0, 0); // draw with red line boolean drawRect = true; boolean drawAnX = true; if (drawRect) { fill(0, 200, 0); // fill with green rect(30, 30, 40, 40); } if (drawAnX) { line(0, 0, 100, 100); line(100, 0, 0, 100); }

Loops Sometimes you want to execute code multiple times – E.g. draw() is being called in a loop Java provides a number of looping mechanisms They all test some boolean expression (just like an if statement does) and continue to execute code while the expression is true May 21, 2010IAT 33425

while loops while( ) { } Repeatedly executes the code body while the boolean expression is true May 21, 2010IAT 33426

for loops for( ; ; ) { } First executes the initialization statement Then tests the boolean expression – if it's true, executes the code once Then repeats the following: – execute final statement, – test boolean expression  execute code if true May 21, 2010IAT 33427

Converting for to while Seeing how for loops can be converted to while loops helps you understand for for( ; ; ) { } // is the same as ; while( ) { ; } May 21, 2010IAT 33428

setup() setup() is a predefined Processing method that you define setup() is called once when a sketch first starts executing Place any startup code in setup(), eg. – Setting the size – Setting the background color – Initializing variables… May 21, 2010IAT 33429

draw() draw() is a predefined Processing method that you define draw() is called repeatedly by the Processing system Put code in draw() when you need to constantly update the display (for example, animating an object) May 21, 2010IAT 33430

Example of setup() and draw() int x; int y; void setup() { size(400, 400); background(0); x = 0; y = height/2; } void draw() { background(0); ellipse(x, y, 20, 20); x = x + 1; if (x > width) x = 0; } May 21, 2010IAT 33431

setup() and draw() are examples of callbacks A callback function is defined by the programmer – The callback gets called in response to some internal event – You usually don’t call callback functions directly with your own code. – setup() and draw() are predefined within Processing as to-be-called-if-defined May 21, 2010IAT 33432

Controlling draw() frameRate() can be used to set the number of times per second that draw() is called – frameRate(30) says to call draw() 30 times a second (if the computer is capable) delay() delays execution for a certain number of milliseconds – delay(250) delays for 250 milliseconds (1/4 of a sec.) – You can use delay() or frameRate() to determine how fast you want draw() to be called – frameRate() is probably easier noLoop() tells the system to stop calling draw() – If you want to, for example, turn off animation loop() tells the system to start calling draw() again – Use noLoop() and loop() together to turn repeated drawing on and off May 21, 2010IAT 33433

June 4, 2010IAT Now I’d like to specify rotation To rotate the figure, I’d need to figure out the new position of the vertices – Too hard! Instead of rotating the figure, rotate the paper – As long as I’m rotating the paper, I may as well slide it around as well To prepare for translating and rotating, first draw the figure centered around the origin (0,0)

June 4, 2010IAT Add translation and rotation void drawRocket(int x, int y, float rot) { final int halfHeight = 10; final int halfWidth = 10; translate(x, y); rotate(rot); triangle(0, -halfHeight, -halfWidth, halfHeight, halfWidth, halfHeight); rectMode(CORNERS); rect(-halfWidth + 5, halfHeight, -halfWidth + 8, halfHeight + 3); rect(halfWidth - 8, halfHeight, halfWidth - 5, halfHeight + 3); } Let’s try drawing several rockets

June 4, 2010IAT Works fine for one call… But when we call it twice, it doesn’t seem to work – Looks like first call messes up subsequent calls What happening is that, when you move the paper (translate, rotate) the paper stays moved Subsequent paper moves (additional translates and rotates) build on top of the previous ones What we want is to move the paper, draw, and move it back We need pushMatrix() and popMatrix() – pushMatrix() remembers the previous paper position (previous transformation matrix) – popMatrix() restores the paper to the remembered position (restores the transformation matrix)

June 4, 2010IAT Using pushMatrix() and popMatrix() void drawRocket(int x, int y, float rot) { final int halfHeight = 10; final int halfWidth = 10; pushMatrix(); translate(x, y); rotate(rot); triangle(0, -halfHeight, -halfWidth, halfHeight, halfWidth, halfHeight); rectMode(CORNERS); rect(-halfWidth + 5, halfHeight, -halfWidth + 8, halfHeight + 3); rect(halfWidth - 8, halfHeight, halfWidth - 5, halfHeight + 3); popMatrix(); }

Mouse variables mouseX and mouseY – variables that automatically contain the current mouse location – pmouseX and pmouseY hold the previous location mousePressed – boolean variable that is true if a mouse button is down – mouseButton – value is LEFT, RIGHT or CENTER depending on which button is held down May 21, 2010IAT 33438

Mouse callback methods There are several built-in methods you can fill in to process mouse events mousePressed() mouseReleased() mouseMoved() mouseDragged() Example: void mousePressed() { if( mouseButton == LEFT ){ println( “Left Mouse Button was pressed” ); loop(); // activate drawing again } May 21, 2010IAT 33439