Programming games
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Programming games Context of what we are doing. Drawing on canvas. Homework: [Complete coin toss examples.] Do your own drawings. Upload files to website.
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Programming games. Drawing on canvas. Homework: [Complete coin toss examples.] Do your own drawings. Upload files to website. HTML5 drawing on canvas. canvas is a new type of element drawing is done using what is termed the 2d context of a drawing element - PowerPoint PPT Presentation
Transcript of Programming games
Programming gamesContext of what we are doing.
Drawing on canvas. Homework: [Complete coin toss examples.]
Do your own drawings. Upload files to website.
RecallSource of diagram: Coursera course Programming for Everyone, (Python), Charles Severance, U of Michigan
Computer can be connected to other computers….
Software• A browser can open files on secondary storage OR
go to the Internet (using the Purchase server).• An editor creates and/or opens and modifies a file
on the local file system.• An ftp program uploads or downloads from your
account on a Purchase server.
Your program
Correct terminology• We use the Filezilla program—it runs file
transfer protocol– to upload and download our work. We do NOT store our files on Filezilla.
• We use Google (on google.com or the google ap) to find web sites. These are mainly NOT google web sites.
• BUT, later in the course, we will use google sites for information on the Google Maps API.
HTML5 drawing on canvas
• canvas is a new type of element• drawing is done using what is termed the
2d context of a drawing element– This requires statement done AFTER the
body is loaded
• can draw rectangles, paths (lines and arcs), images, text, and image from a video!– can also display video element directly.
Screen geometry
• Origin is upper left corner!!!!• units are pixels (very small)• Sometimes the terms top or y is used for vertical
– vertical values increase going down the screen
• Sometimes the terms left or x is used for horizontal– horizontal values increase going to the right.
• Screen geometry holds for Flash and Processing and some, though not all, programming languages/environments.
Drawings
• Default color is black.• Drawing done for stroke versus fill.• Colors are set using
– Names: for 16 specific colors and othershttp://www.tutorialspoint.com/html5/html5_color_names.htm.
– red-green-blue values, each as numbers 0 to 255
– hexadecimal
0,0, default color, 10 by 10, stroke
0,300,green,30 by 30, stroke
500,300, 50 by 50, fill
500,0,default color,20 by 20, fill
rgb(200,0,100)
<!DOCTYPE html><html> <head> <title>Four rectangles</title><script>var ctx;function init() { ctx = document.getElementById('canvas').getContext('2d'); ctx.lineWidth = 2; ctx.strokeRect(0,0,10,10); ctx.fillRect(500,0,20,20); ctx.strokeStyle = "green"; ctx.fillStyle = "rgb(200,0,100)"; ctx.strokeRect(0,300,30,30); ctx.fillRect(500,300,50,50); }</script> </head><body onLoad="init();"><canvas id="canvas" width="600" height="400"> Your browser
doesn't support the HTML5 element canvas.</canvas> </body> </html>
Errors
• JavaScript is scripting language: interpret statements at execution time.– NOT compiled, with error messages
• Semantic errors (errors of meaning) are more difficult to detect and fix!
• Syntactic errors are errors of form, analogous to grammatical errors– FireFox Tools/Error Console can help
• Most common: bad bracketing• ctx.fillStyle("rgb(200,0,100)"); fillStyle is attribute,not method
Comments• The drawing is done by the init function which is
called when the body element is loaded. The canvas element with id="canvas" does not exist until the body is loaded.– if there was more than one canvas element, we would
use different names for the ids.• Default color is black. Red green blue values
each are 0 to 255 (8 bits of intensity). The strokeStyle and the fillStyle are attributes, not methods.
• GO: experiment with colors (by name) and rgb (note the quotation marks) and location and width and height.
Classwork
Do this now even if you haven't finished the coin toss programs.
• After you get my example working, change it!– Put rectangles of different sizes in different
places.– Change colors.
Confirm that your code does what you intended.
More comments
• Drawings are …paint on the canvas.• These rectangles are not objects to be
moved or referenced later.• Use ctx.clearRect(…) method to erase. • Need to do calculations to detect hits.
– See memory game in book.
• Alternative is dynamic placement of html markup– See quiz, hangman.
Reading code: sketch<html> <head> <title> Stuff </title><script>var ctx;function init() { ctx = document.getElementById('canvas').getContext('2d'); ctx.lineWidth = 10; ctx.fillStyle = "green"; ctx.fillRect(500,10,150,300); ctx.strokeStyle = "pink"; ctx.strokeRect(10,320,650,30); }</script> </head><body onLoad="init();"><canvas id="canvas" width="900" height="600"> Your
browser doesn't support the HTML5 element canvas.</canvas> </body> </html>
Images
var himg = new Image();himg.src = "head.jpg";var timg = new Image();timg.src = "tail.jpg";…ctx.drawImage(himg,100,200, 60,60);
or if you set x, y, w, h variables set appropriately
drawImage(himg, x, y, w, h);
Notice• Compare img and Image
– img is the html element type– Image is the built-in JavaScript object
• In html document:– Elements: <html >, <body >, <a >, <img >– Elements are
• Singletons: <img > Proper way is <img … />
• or pairs: <a…>…. </a>
– Elements can contain attributes• <a href=….>, <img src=….>, <body onLoad=…>
– Elements can contain text and/or other elements– html document contains head and body
• head contains title, style, script• body contains
Write in notebook
Advice: Take notes• Key concepts
• Questions & clarifications
• Ideas– Drawings– Combining what you know
• Random choice• Changing img src• Changing input values in a form• Drawing on canvas
– More drawing tools coming
From now on…
• Modify (add to) your index.html file.
• Using Filezilla,– Upload new programs
• The .html file and any other files
– Upload modified index.html file
• Also, can use web space or FILE space for unfinished work
Filezilla
• Demonstration
Classwork / homework
• [Finish basic coin toss, biased coin, counts]• Practice drawings (your drawings).• Preview (more in next class): coin toss drawing images
on canvas.– Saving it as new file, change your basic coin toss to draw
images on the canvas.• consult tutorial.
– You can do this. You can look at other examples. Look online for help.
– The logic is pretty much the same.– The body element needs to hold a canvas element and a button
element. The script element sets the ctx variable.
