Functions. Functions. nofill(); point(20, 30); float angle = map(i, 0, 10, -2, 2); parameters return values

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1 Functions parameters return values 06 Functions 1 Functions Code that is packaged so it can be run by name Often has parameters to change how the function works (but not always) Often performs some computation and returns a value (but not always) We use functions all the time in Processing nofill(); point(20, 30); float angle = map(i, 0, 10, -2, 2); We can also define our own custom functions 06 Functions 2

2 Why Custom Functions? Custom functions make code modular Modular code is: - easier - easier to reuse to test Credit: Credit: 06 Functions 3 Anatomy of a Function without Parameters void means it returns nothing function name empty brackets means no parameters void tree() { nostroke(); // trunk fill(#5a3709); // brown quad(45, 40, 55, 40, 60, 90, 40, 90); // leaves fill(#5cbf17); // green ellipse(50, 30, 55, 55); 06 Functions 4

3 landscape1 void draw() { coding tree(); function comments // draw tree // with bottom of trunk at 50, 90 void tree() { nostroke(); // trunk fill(#5a3709); quad(45, 40, 55, 40, 60, 90, 40, 90); // leaves fill(#5cbf17); // green ellipse(50, 30, 55, 55); 06 Functions 5 Calling Functions You must call your custom functions or they won t execute Processing calls setup and draw for you - setup and draw are built-in functions that you customize Defining Functions Define your functions outside setup and draw - the same place global variables are defined 06 Functions 6

4 function is called function returns 06 Functions 7 (demos) declaration order doesn't matter void printb() { print("b "); printa(); print("setup "); printb(); void printa() { print("a "); 06 Functions 8

5 What does this Output? print("apple "); saybanana(); sayorange(); void sayorange() { print("orange "); void saybanana() { print("banana "); A. apple B. orange C. banana orange D. apple orange banana E. apple banana orange 06 Functions 9 Anatomy of a Function with Parameters void means it returns nothing function name function parameters void tree(float x, float y) { nostroke(); // trunk fill(#5a3709); // brown quad(x - 5, y - 50, x + 5, y - 50, x + 10, y, x - 10, y); // leaves fill(#5cbf17); // green ellipse(x, y - 60, 55, 55); 06 Functions 10

6 Function Arguments function name arguments tree(40, 150); 06 Functions 11 landscape2... coding // use the tree function to // create a forest tree(40, 90); tree(100, 90); tree(160, 90); function comments // draw tree // x, y position (centre bottom of trunk) void tree(float x, float y) { nostroke(); // trunk fill(#5a3709); // brown quad(x - 5, y - 50, x + 5, y - 50, x + 10, y, x - 10, y); // leaves fill(#5cbf17); // green ellipse(x, y - 60, 55, 55); 06 Functions 12

7 06 Functions 13 What does this Output? fruit(-1); print("apple "); void fruit(int a) { if (a > 0) { print("orange "); else { print("banana "); A. apple B. fruit apple C. banana apple D. orange apple E. orange banana apple 06 Functions 14

8 Calling Functions You must call your custom functions or they won t execute Processing calls setup and draw for you - setup and draw are built-in functions that you customize Defining Functions Define your functions outside setup and draw - the same place global variables are defined You cannot define more than one custom function with the same name and same parameter types 06 Functions 15 Defining Multiple Functions with Same Name void tree() {... void tree(float x, float y) {... void tree(float x) {... void tree(float treex, float treey) { Functions 16

9 float vs. int parameters These are different functions void tree(float x, float y) {... void tree(int x, int y) { Functions 17 Function Signature the signature of a function is: - the function name - the parameter types (in order) These are all different function signatures: void tree() void tree(float x) void tree(float x, float y) void tree(int x, int y) void tree(boolean b, int a) void tree(int a, boolean b) the order of parameter types is different, so different signatures 06 Functions 18

10 vehicle // draw a vehicle // x, y is position of centre bottom // hue hue to fill the car body // (0 to 360 degrees) void vehicle(int x, int y, float hue) { // top part stroke(0); fill(hue, 100, 100); // orange rect(x - 20, y - 40, 40, 30); fill(150); // gray // front wheel ellipse(x - 20, y - 10, 20, 20); // back wheel ellipse(x + 20, y - 10, 20, 20); 06 Functions Functions 20

11 Function attributes are passed-by-value passed-by-value means the function parameter is a copy of an attribute variable changing the value of a parameter will not change the attribute variable int a = 10; println(a); // 10 f(a); println(a); // 10 int a = 10; println(a); // 10 f(a); println(a); // 10 void f(int b) { b = b + 1; void f(int a) { a = a + 1; 06 Functions 21 Functions and Scope Custom functions can access global variables, (just like setup and draw) Custom functions can have local variables, (just like setup and draw) 06 Functions 22

12 landscape3 // draw trees behind with a for loop for (float x = 50; x < width; x += 100) { tree(x, 90);... // draw the car vehicle(vehiclex, 92, vehiclehue); // draw trees in front with a while loop float x = 100; while (x < width) { tree(x, 95); x = x + 100; 06 Functions 23 What will you see? void draw() { a(); ellipse(25, 50, 50, 50); b(); ellipse(75, 50, 50, 50); void a() { strokeweight(10); fill(128); // grey void b() { strokeweight(2); fill(255); // white A C B D nothing, it s an error 06 Functions 24

13 What will you see? void draw() { a(); ellipse(25, 50, 50, 50); b(); ellipse(75, 50, 50, 50); void a() { strokeweight(10); fill(128); // grey b(); void b() { strokeweight(2); fill(255); // white A C B D nothing, it s an error 06 Functions 25 returns nothing void myfunc(float a, floa returns something int myfunc(float a, floa 06 Functions 26

14 Functions that Return Values We use functions that return values all the time: float x = random(1, 100); float a = map(x, 1, 200, 20, 30); fill(random(255)); arc(0, 0, 10, 10, 0, radians(45)); 06 Functions 27 A Function with a Return Value float is the return type function name function parameters float sum (float a, float b, float c) {... return ; this is where the value is returned 06 Functions 28

15 Example return type is int int sum(int a, int b, int c) { int total = a + b + c; return total; required return statement 06 Functions 29 Function Calling Tracethrough int answer = sum(1, 2, 3); int sum(int a, int b, int c) { int total = a + b + c; return total; 06 Functions 30

16 Trace int answer = sum(1, 2, 3); int sum(int a, int b, int c) { int total = a + b + c; return total; 06 Functions 31 Trace int answer = sum(1, 2, 3); int sum(int a, int b, int c) { int total = a + b + c; return total; 06 Functions 32

17 Trace int answer = sum(1, 2, 3); a = 1 b = 2 c = 3 int sum(int a, int b, int c) { int total = a + b + c; return total; 06 Functions 33 Trace int answer = sum(1, 2, 3); int sum(int a, int b, int c) { int total = a + b + c; return total; 06 Functions 34

18 Trace int answer = sum(1, 2, 3); total = 6 int sum(int a, int b, int c) { int total = a + b + c; return total; 06 Functions 35 Trace int answer = sum(1, 2, 3); int sum(int a, int b, int c) { int total = a + b + c; return total; 06 Functions 36

19 Trace int answer = sum(1, 2, 3); int sum(int a, int b, int c) { int total = a + b + c; return total; 06 Functions 37 Trace int answer = sum(1, 2, 3); sum(1, 2, 3) = 6 int sum(int a, int b, int c) { int total = a + b + c; return total; 06 Functions 38

20 Trace int answer = sum(1, 2, 3); answer = 6 int sum(int a, int b, int c) { int total = a + b + c; return total; 06 Functions 39 Analogy setup() sum( ) 06 Functions 40

21 Analogy a = 1 b = 2 c = 3 setup() sum( ) 06 Functions 41 Analogy a + b + c setup() sum( ) 06 Functions 42

22 Analogy 6 setup() sum( ) 06 Functions 43 Analogy setup() sum( ) 06 Functions 44

23 sumfunction int x = sum(2, 4, 6);... int sum(int a, int b, int c) { int total = a + b + c; return total; 06 Functions 45 sumfunction int x = sum(2, 4, 6); int y = sum(23, 45, 71) / 2; int z = sum(x, y, 10); line(0, 0, width, sum(x, y, z)); int sum(int a, int b, int c) { int total = a + b + c; return total; 06 Functions 46

24 Using Functions with Return Values Can use function that returns values anywhere you use the same type of value, e.g. // a = 12 int a = sum(2, 4, 6); // b = 12 * 100 b = sum(2, 4, 6) * 100; // c = ( ) c = sum(2, 4, sum(2, 4, 6)); // point(12, 10) point(sum(2, 4, 6), 10); // if (4 > 3) {... if (sum(2, 4, 6) > 3) { Functions 47 What does this Output? print(double(1)); int double(int a) { int r = a + a; return r; A. 1 B. 2 C. r D. double E. nothing, it s a syntax error 06 Functions 48

25 What does this Output? print(double(double(1))); int double(int a) { int r = a + a; return r; A. 1 B. 2 C. 3 D. 4 E. nothing, it s a syntax error 06 Functions 49 What does this Output? print(triple(1)); int triple(int a) { int r = a + a + a; A. 1 B. 2 C. 3 D. 4 E. It s a syntax error 06 Functions 50

26 Possible Logic Error Need to assign the return value to something - it may be a logic error if you don t sum(3, 6, 9); // nothing assigned random(1, 1000); // nothing assigned 06 Functions 51 Defining Multiple Functions with Same Name int sum(int a, int b, int c) {... int sum(int a, int b, int c, int d) {... float sum(int a, int b, int c) {... void sum(int a, int b, int c) {... can t have same name with same parameters but different return types 06 Functions 52

27 mymax1 // returns the largest number (a or b) float mymax(float a, float b) { float largest; if (a > b) { largest = a; else { largest = b; return largest; 06 Functions 53 mymax (unit tests) // unit tests println(mymax(5, 10)); // answer is 10 println(mymax(15, 10)); // answer is 15 println(mymax(-500, 10)); // answer is 10 println(mymax(0.5, 0.1)); // answer is 0.5 println(mymax(10, 10)); // answer is Functions 54

28 mymax2 (early return) // returns the largest number (a or b) float mymax(float a, float b) { if (a > b) { return a; else { return b; 06 Functions 55 Processing has built-in functions max and min can accept 2 or 3 arguments returns float or int depending what argument types closely related to constrain max(a, b) max(a, b, c) min(a, b) min(a, b, c) 06 Functions 56

29 Circle Hit Testing (Bounds Detection) Radius is the distance between circle centre to circle edge If distance from mouse to circle center is less than radius, then circle is hit (e.g. rollover, clicked on, etc.) 06 Functions 57 Distance Between Two Points strokeweight(10); point(77, 81); // P point(13, 45); // Q // calculate distance // between point P and Q float d = how to do this? 06 Functions 58

30 Pythagorean Theorem 06 Functions 59 mydist use built-in function sqrt() for square root // returns the distance between // point P at (px, py) and point Q at (qx, qy) float mydist(float px, float py, float qx, float qy) { float a = px - qx; float b = py - qy; float d = sqrt((a * a) + (b * b)); return d; 06 Functions 60

31 circlehittest // returns true if px, py is inside a circle // that is centred at cx, cy with radius r boolean circlehittest(float px, float py, float cx, float cy, float r) { float d = mydist(px, py, cx, cy); if (d < r) { return true; else { return false; 06 Functions 61 Processing has a built-in function for distance returns float dist(x1, y1, x2, y2) Use this built-in dist function to calculate the distance between two points in your labs and assignments! 06 Functions 62

32 Extra: Mouse Speed The distance between the current mouse position and the previous mouse position is the speed of the mouse - pmousex and pmousey are built-in global variables for the previous mouse position float speed = dist(mousex, mousey, pmousex, pmousey); since we calculate it each time draw is called, the speed will be in pixels per frame - since framerate is 60 frames per second, multiply by 60 to get pixels per second 06 Functions 63 maxspeed float maxspeed = 0; void draw() { background(245); // almost white float speed = dist(mousex, mousey, pmousex, pmousey); // update the max speed so far if (speed > maxspeed) { maxspeed = speed; // display the max speed and current speed fill(0); // black text(round(maxspeed), width / 2, height / 2-40); text(round(speed), width / 2, height / ); 06 Functions 64

33 mousespeed size(300, 300); nostroke(); background(245); // almost white void draw() { float speed = dist(mousex, mousey, pmousex, pmousey); // draw an ellipse with size representing speed fill(0, 50); // semi transparent black ellipse(mousex, mousey, speed, speed); 06 Functions 65