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Keyboard and Events

Keyboard and Events. Fall 2009. Simply displaying text. // Step 1: Create the font using the Tool menu option // Step 2: Declare PFont variable PFont f; void setup() { size(200,200); // Step 3: Load Font f = loadFont( "Albany-48.vlw" ); } void draw() { background(255);

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Keyboard and Events

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  1. Keyboard and Events Fall 2009

  2. Simply displaying text // Step 1: Create the font using the Tool menu option // Step 2: Declare PFont variable PFont f; void setup() { size(200,200); // Step 3: Load Font f = loadFont( "Albany-48.vlw" ); } void draw() { background(255); textFont(f,16); // Step 4: Specify font to be used fill(0); // Step 5: Specify font color // Step 6: Display Text text ( "Mmmmm ... Strings ..." ,10,100); }

  3. What are Strings? • String is a data type (like int or char) • It stores collections of characters (i.e., chars) that are delineated by quotes. char letter =‘b’; String word = “this is more than one word”; • Any character on the keyboard (including numbers) can be part of a String

  4. You try it! // Step 1: Create the font using the Tool menu option // Step 2: Declare PFont variable PFont f; void setup() { size(200,200); // Step 3: Load Font f = loadFont( “you fill this in" ); } void draw() { background(255); textFont(f, you fill this in); // Step 4: Specify font fill(0); // Step 5: Specify font color // Step 6: Display Text String message = “you fill this in" ; text (message,10,100); }

  5. What about the keyboard? // Draw a line when any key // is pressed void setup() { size(100, 100); smooth(); strokeWeight(4); } void draw() { background(204); if (keyPressed == true) { line(20, 20, 80, 80); } } • Keyboard inputs can be used in many ways---not just for text • The boolean variable keyPressed is true if a key is pressed and false if not. • keyPressed is true as long as a key is held down

  6. Another example with keyPressed // Move a line while any key is pressed int x = 20; void setup() { size(100, 100); smooth(); strokeWeight(4); } void draw() { background(204); if (keyPressed == true) { // If the key is pressed x++; // add 1 to x } line(x, 20, x-60, 80); }

  7. You can also display text • The key variable is of type char and stores the most recently pressed key PFont font; void setup() { size(100, 100); font = loadFont("Tahoma-Bold-18.vlw"); textFont(font); } void draw() { background(0); text(key, 28, 75); }

  8. But characters are really numbers • Each character has a numerical value defined by the ASCII code int x = 0; void setup() { size(100, 100); } void draw() { if (keyPressed == true) { x = key - 32; rect(x, -1, 20, 101); } }

  9. Coded Keys color y = 35; void setup() { size(100, 100); } void draw() { background(204); line(10, 50, 90, 50); if (key == CODED) { if (keyCode == UP) { y = 20; } else if (keyCode == DOWN) { y = 50; } } else { y = 35; } rect(25, y, 50, 30); } • Processing can also read the value from other keys such as the arrow keys, Alt, Shift, Backspace, Tab and others (see page 227) • Check that the key is coded first: key==CODED

  10. In-class exercise • Use the arrow keys to change the position of a shape within the canvas.

  11. Flow of Control • Programs can broadly be classified as being • Procedural • Programs are executed once in the order specified by the code varied only by loops and function calls. • Event Driven • Programs run continuously responding to input events such as key strokes or mouse clicks.

  12. Refresher… • Today we review events for event driven programs. • First event driven program void draw() { frameRate(4); //fps = 4 println(frameCount); }

  13. What Happened? • About 4 times per second, a number (the frame count) was printed to the console window. • Why? • There’s no for loop or while loop? • The draw() function is processed continuously by the event handler until another event is triggered or you press the STOP button.

  14. More on Why • Specifically the draw() function is called 4 times per second since we set the frameRate to 4. • Remove the frameRate() line and see what happens. • What’s the default frame rate?

  15. Next Program float gray = 0; void setup() { size(100, 100); } void draw() { background(gray); } void mousePressed() { gray += 20; }

  16. Change It • Change the mousePressed() to mouseReleased(). • What happens differently? • Move the background() call to mouseReleased(). Now draw() is empty? Can we remove it? • Why or why not? • Add a background() call inside draw() • What happens? Why?

  17. draw() • Event Driven Programs • Programs run continuously responding to input events such as key strokes or mouse clicks. • Without the draw() function, our program is no longer listening for events.

  18. What Happened? • About 4 times per second, a number (the frame count) was printed to the console window. • Why? • There’s no for loop or while loop? • The draw() function is processed continuously by the event handler until another event is triggered or you press the STOP button.

  19. For Something Different void setup() { size(100, 100); fill(0, 102); } void draw() { } // Empty draw() keeps the program running void mousePressed() { rect(mouseX, mouseY, 33, 33); }

  20. mouseMoved() & mouseDragged() • What’s the difference between a dragged mouse and a moved mouse? If you don’t know, run this program and find out! int dragX, dragY, moveX, moveY; void setup() { size(100, 100); smooth(); noStroke(); } //continues on next slide

  21. mouseMoved() & mouseDragged()[continued] void draw() { background(204); fill(0); ellipse(dragX, dragY, 33, 33); // Black circle fill(153); ellipse(moveX, moveY, 33, 33); // Gray circle } void mouseMoved() { // Move gray circle moveX = mouseX; moveY = mouseY; } void mouseDragged() { // Move black circle dragX = mouseX; dragY = mouseY; }

  22. Built-in Variables • mouseX • mouseY • Do you remember what these are? Look at the code you just ran? If you need to print them out to help figure out what they are.

  23. Key Events • keyPressed() • keyReleased() • Look for the built-in or predefined variable key. What is it? • A character value is depicted in single quotes like ‘a’. But an ‘a’ also has a numeric representation which is the value 97. You can look at an ascii table to see all character values. The character value ‘A’ is equal to 65. What is the character ‘Q’ equal to?

  24. Another keyPressed() Example - testing a value boolean drawT = false; void setup() { size(100, 100); noStroke(); } void draw() { background(204); if (drawT == true) { rect(20, 20, 60, 20); rect(39, 40, 22, 45); } } //contined on next slide

  25. Another keyPressed() Example - testing a value void keyPressed() { if ((key == 'T') || (key == 't')) { drawT = true; } } void keyReleased() { drawT = false; }

  26. Using Strings // An extremely minimal text editor, it can only insert // and remove characters from a single line PFont font; String letters = ""; void setup() { size(100, 100); font = loadFont("Eureka-24.vlw"); textFont(font); stroke(255); fill(0); } void draw() { background(204); float cursorPosition = textWidth(letters); line(cursorPosition, 0, cursorPosition, 100); text(letters, 0, 50); } // continued on next slide

  27. Using Strings void keyPressed() { if (key == BACKSPACE) { // Backspace if (letters.length() > 0) { letters = letters.substring(0, letters.length()-1); } } else if (textWidth(letters+key) < width){ letters = letters+key; } } • What do you think letters.substring(), letters.length and textWidth() do?

  28. letters.substring(), letters.length() and textWidth() • letters.substring() • http://processing.org/reference/String_substring_.html • letters.length() • http://processing.org/reference/String_length_.html • textWidth() • http://processing.org/reference/textWidth_.html

  29. Flow Control • frameRate() • Sets a limit as to how many frames are displayed per second • loop() • Resumes continuous draw() calls • noLoop() • Stops draw() from repeated being called • redraw() • Calls draw() once

  30. int frame = 0; void setup() { size(100, 100); frameRate(30); } void draw() { if (frame > 60) { // If 60 frames since the mouse noLoop(); // was pressed, stop the program background(0); // and turn the background black. } else { // Otherwise, set the background background(204); // to light gray and draw lines line(mouseX, 0, mouseX, 100); // at the mouse position line(0, mouseY, 100, mouseY); frame++; } } void mousePressed() { loop(); frame = 0; }

  31. Run This and Then Remove Comments in setup() void setup() { size(100, 100); //noLoop(); // what happens when noLoop is uncommented } void draw() { background(204); line(mouseX, 0, mouseX, 100); } void mousePressed() { redraw(); // Run the code in draw one time }

  32. Your Turn • Create a shape that has events defined for mousePressed, mouseDragged, mouseReleased and keyPressed where key equals some particular value. For example an ‘L’ draws a line.

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