I am making a game in which the collision between letters and boxes must be detected.
I came across width height comparison algorithm but how would I go about finding the letters's height and width properties?
<!DOCTYPE html>
<html>
<head>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<title>Game</title>
</head>
<style>
#canvas{
outline: 1px solid #000;
background-color: #0099FF;
}
</style>
<body>
<canvas id="canvas" width="800" height="600">
</canvas>
<script>
var canvas = document.querySelector('#canvas');
var ctx = canvas.getContext("2d");
ctx.fillStyle = "#FF5050";
var xPos=0;
var yPos=500;
ctx.fillRect(xPos,yPos,70,70);
ctx.stroke();
function move(e){
if(xPos+70<=canvas.width)
{
if(e.keyCode==39){
xPos+=5;
}
}
if(xPos>0)
{
if(e.keyCode==37){
xPos-=5;
} }
canvas.width=canvas.width;
ctx.fillStyle = "#FF5050";
ctx.fillRect(xPos,yPos,70,70);
ctx.stroke();
}
document.onkeydown =move;
</script>
<script>
var letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
function randomNumber(max) {
var randomNum = Math.random();
var numExpanded = randomNum * max;
var numFloored = Math.floor(numExpanded);
return numFloored;
}
//create a function returning a random letter
function randomLetter() {
var random0to25 = randomNumber(letters.length);
var randomLetter = letters.charAt(random0to25);
return randomLetter;
}
//create a function creating a span containing a random letter and attaching it to body
function createLetter() {
var span = $("<span/>");
span.css("position", "absolute");
span.css("top", 0);
randomCol=randomNumber(760);
randomCol=randomCol+20;
//concatenation
span.css("left", randomCol+"px");
span.text(randomLetter());
span.appendTo("body");
return span;
}
//explain how to animate an element
function makeLetterFall() {
var letterElement = createLetter();
letterElement.animate({"top":"95%"}, 5000); //any ideas how not to use {} here?
}
//handle keyup, find a letter and remove it
/*function removeTypedLetter(pressedKey) {
var typedLetter = String.fromCharCode(pressedKey.keyCode);
var letterElement = $("span:contains("+typedLetter+")").first();
letterElement.remove();
}*/
//$(document).on("keyup", removeTypedLetter);
//make a new letter every second
setInterval(makeLetterFall, 1000);
</script>
</body>
</html>
It's probably easier to use canvas to draw both the falling letter and the blocks.
That way you can get the text's bounding box like this:
set the text font with context.font='36px verdana'
The approximate text height is the px font size + 2 (in this example var textHeight=36+2;)
You can measure the text width using var textWidth=context.measureText('A').width
Bounding box: x,y,textWidth,textHeight
To detect collisions you would check the text's bounding box against each rectangle's bounding box:
var textLeft=textX;
var textRight=textX+textWidth;
var textTop=textY;
var textBottom=textY+textHeight;
var rectLeft=rectX;
var rectRight=rectX+textWidth;
var rectTop=rectY;
var rectBottom=rectY+rectHeight;
// test if text & rect are colliding
return(!(
textLeft>rectRight ||
textRight<rectLeft ||
textTop>rectBottom ||
textBottom<rectTop
));
You can draw text on the canvas like this:
// context.fillText(text,x,y);
context.fillText('A',100,200);
To animate the text falling, in each new frame you would clear the canvas with context.clearRect(0,0,canvas.width,canvas.height) and then redraw the blocks & text in their new positions.
Related
Can anyone please help me identify why this code isn't working? It's copied directly from a youtube tutorial so I can't see where I've gone wrong!
Thank you!
I basically want to create matrix rain, but my own version of symbols within it. Would someone be able to correctly identify what's wrong with this code? I have tried to input it into http://phptester.net/
<DOCTYPE html>
<html>
<head>
<title>Matrix Rain</title>
<style>
/*basic resets */
* {margin:0; padding: 0;}
/* adding a black bg to the background to make things clearer */
body {background: black;}
canvas {display: block;}
</style>
</head>
<body>
<canvas id="c"></canvas>
<script type="text/javascript">
var c = document.getElementbyId("c");
var ctx = c.getCont("2d");
//making the canvas full screen
c.height = window.innerHeight;
c.width = windows.innerWidth;
var ganoti = "诶比西迪艾弗艾尺艾勒艾娜吉吾艾儿"
//converting the string into an array of single characters
chinese = chinese.split ("");
var font_size = 10;
var columns = c.width/font_size; //number of columns for rain
//an array of drops - one for column
var drops = [];
//x below is the x coordinate
//1 = y co-ordinate of the drop(same for every drop initially)
for (var = x; x < columns; x++)
drops[x] = 1;
//drawing the characters
function draw () {
//Black BG for the canvas
//translucent BG to show trail
ctx.fillStyle - "rgba(0,0,0,0.05)";
ctx.fillRect(0,0, c.wdith, c.height);
ctx.fillstyle = "DB7093";
ctx.font = font_size + "px arial";
//looping over drops
for (var i = 0; i < drops.length; i++) {
var text = ganoti[Math.floor(Math.random()*ganoti.lenth)];
//x = i*font_size, y = value of drops[i]*font_size
ctx.fillText(text, i*font_size, drops[i]*font_size);
//sending the drop back to the top randomly after it has crossed
screen // it should be in comment line
//adding a randomness to the reset to make the drops scattered on the
Y axis // it should be in comment line
if (drops[i]*font_size > c.height && Math.random() > 0.975)
drops[i] = 0;
//incrementing Y coordinate
drops[i]++
}
}
setInterval(draw, 33);
</script>
</body>
</html>
}
}
phptester.net requires PHP, your code is HTML, besides has redundant double } in the end.
I am trying to create a rect that moves on keypress for a pong game and when I press the key the left rect disappears..
Any ideas how to fix the problem? It is really important..
The code is written in vanilla javascript so please don't write jQuery..
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Pong</title>
<script type="text/javascript">
var x = 100;
var y = 100;
var xmoveFirst = 720;
var ymoveFirst = 0;
var xmoveSecond = 30 ;
var ymoveSecond = 0;
function canvas() {
var can = document.getElementById('theCanvas');
can.style.backgroundColor = "black";
var ctx = can.getContext('2d');
//first player
ctx.fillStyle="white";
ctx.fillRect(xmoveFirst,ymoveFirst,5,75);
//second player
ctx.fillStyle = 'white';
ctx.fillRect(xmoveSecond,ymoveSecond,5,75);
//first player move
function moveFirst(eFirst) {
ctx.clearRect(0,0,750,750); //clear rects
if (eFirst.keyCode == 40) {
ymoveFirst+=25;
console.log("first,"+ymoveFirst);
}
else if (eFirst.keyCode == 38) {
ymoveFirst-=25;
console.log("first,"+ymoveFirst);
}
ctx.fillStyle="white";
ctx.fillRect(xmoveFirst,ymoveFirst,5,75);
ctx.fillRect(xmoveSecond,ymoveSecond,5,75);
}
var first = document.onkeydown = moveFirst;
//second player move
function moveSecond(eSecond) {
ctx.clearRect(0,0,750,750);
if (eSecond.keyCode == 83) {
ymoveSecond+=25;
console.log("second,"+ymoveSecond);
}
else if (eSecond.keyCode == 87) {
ymoveSecond-=25;
}
ctx.fillStyle="white";
ctx.fillRect(xmoveFirst,ymoveFirst,5,75);
ctx.fillRect(xmoveSecond,ymoveSecond,5,75);
console.log("second,"+ymoveSecond)
}
var second = document.onkeydown = moveSecond;
}
83,87
</script>
</head>
<body onload="canvas()">
<canvas id="theCanvas" width="750" height="750"></canvas>
</body>
</html>
This line: can.width=can.width; resets the canvas width.
When you change the canvas size (width or height), you clear the canvas (making everything black). After this line, you are only redrawing the rightmost paddle, so the left one remains missing.
You'll need to redraw the leftmost paddle as well if you want it to come back. Here is the modified moveRight() function:
function moveRight(eFirst) {
if (eFirst.keyCode==40) {
ymoveFirst+=25;
console.log(ymoveFirst);
}
else if (eFirst.keyCode==38) {
ymoveFirst-=25;
console.log(ymoveFirst);
}
can.width=can.width;
ctx.fillStyle="white";
// Redraw BOTH paddles
ctx.fillRect(xmoveFirst,ymoveFirst,5,75);
ctx.fillRect(xmoveSecond,ymoveSecond,5,75);
}
Also, replace
document.onkeydown = moveFirst; and document.onkeydown = moveSecond;
with
document.addEventListener("keydown", moveFirst);, and document.addEventListener("keydown", moveSecond);
Currently, you are overwritting the first listener with document.onkeydown = moveSecond;. By using addEventListener, you don't overwrite the ones that already exist.
How the random letters wrapped with rectangles can be generated using canvas??? I used j-query for it but dont know how to do it with canvas. here is the code which generates random letter using j-query.
<script>
var letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
function randomNumber(max) {
var randomNum = Math.random();
var numExpanded = randomNum * max;
var numFloored = Math.floor(numExpanded);
return numFloored;
}
//create a function returning a random letter
function randomLetter() {
var random0to25 = randomNumber(letters.length);
var randomLetter = letters.charAt(random0to25);
return randomLetter;
}
//create a function creating a span containing a random letter and attaching it to body
function createLetter() {
var span = $("<span/>");
span.css("position", "absolute");
span.css("top", 0);
randomCol=randomNumber(760);
randomCol=randomCol+20;
//concatenation
span.css("left", randomCol+"px");
span.text(randomLetter());
span.appendTo("body");
return span;
}
//explain how to animate an element
function makeLetterFall() {
var letterElement = createLetter();
letterElement.animate({"top":"95%"}, 5000); //any ideas how not to use {} here?
}
//handle keyup, find a letter and remove it
/*function removeTypedLetter(pressedKey) {
var typedLetter = String.fromCharCode(pressedKey.keyCode);
var letterElement = $("span:contains("+typedLetter+")").first();
letterElement.remove();
}*/
//$(document).on("keyup", removeTypedLetter);
//make a new letter every second
setInterval(makeLetterFall, 1000);
</script
>
Here's a learning example showing a falling rectangle letter.
Points of interest:
letter width can be measured with context.measureText
letter height can be approximated as the fontsize plus 2-3
text can be aligned vertically & horizontally with .textAlign & .textBaseline
text can be drawn on the canvas with context.fillText('A',x,y)
unfilled rectangles can be drawn on the canvas with context.strokeRect(x,y,width,height)
Example code and a Demo:
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
var x=150;
var y=10;
var fontsize=20;
var fontface='verdana';
ctx.font=fontsize+' '+fontface;
ctx.textAlign='center';
ctx.textBaseline='middle';
animate();
function drawLetter(letter,x,y){
var width=ctx.measureText(letter).width;
ctx.strokeRect(x,y,width,fontsize);
ctx.fillText(letter,x+width/2,y+fontsize/2,width,fontsize);
}
function animate(){
ctx.clearRect(0,0,cw,ch);
drawLetter('A',x,y);
x+=Math.random()*4-2;
y+=1;
if(y<ch){
requestAnimationFrame(animate);
}
}
body{ background-color: ivory; padding:10px; }
#canvas{border:1px solid red;}
<h4>Letter in Rect falling with random horizontal drifting</h4>
<canvas id="canvas" width=300 height=300></canvas>
I want to use onmouseover in this javascript code. So, whenever I move the mouse over the square, the function changeColor executes and picks one color each time, from the two given colors.
<!DOCTYPE html>
<html>
<head>
<title>TEST</title>
</head>
<body>
<h1>Canvas Art Gallary</h1>
<canvas id="myCanvas" width="400" height="300" style="border:10px solid #c3c3c3">
</canvas>
<script type="text/javascript">
function changeColor(){
ctx.fillStyle = "#FFFFFF";
ctx.fillStyle = "#04B45F";
}
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = "#FF0000";
ctx.fillRect(150,100,100,100);
</script>
</body>
</html>
Thanks
Listen for mouse events and toggle the color on our own custom mouseenter
Note: the rect does not have mouseenter so we must custom build one.
Listen for mousemove events
On rect mouseenter: set a wasInside flag to true and changeColor() which toggles the rect color
On rect mouseleave: clear a wasInside flag to indicate the mouse has left the rect.
Example code and a Demo: http://jsfiddle.net/m1erickson/9GcbH/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color:ivory; }
#canvas{border:1px solid red;background-color:black;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var $canvas=$("#canvas");
var canvasOffset=$canvas.offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var scrollX=$canvas.scrollLeft();
var scrollY=$canvas.scrollTop();
var toggle=0;
var x=150;
var y=100;
var w=100;
var h=100;
var wasInside=false;
// draw the rect to start
ctx.fillStyle = "red";
ctx.fillRect(x,y,w,h);
function changeColor(){
if(toggle==0){
ctx.fillStyle = "#FFFFFF";
toggle=1;
}else{
ctx.fillStyle = "#04B45F";
toggle=0;
}
ctx.fillRect(x,y,w,h);
}
function handleMouseMove(e){
e.preventDefault();
var mx=parseInt(e.clientX-offsetX);
var my=parseInt(e.clientY-offsetY);
var isInsideNow=(mx>x && mx<x+w && my>y && my<=y+h);
if(isInsideNow && !wasInside){
changeColor();
wasInside=true;
}else if(!isInsideNow && wasInside){
wasInside=false;
}
}
$("#canvas").mousemove(function(e){handleMouseMove(e);});
}); // end $(function(){});
</script>
</head>
<body>
<h4>Rect color toggles white-green<br>each time mouse moves over it.</h4>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>
[ Addition: explain steps of toggling ]
Each time the mouse enters the rect changeColor is called.
changeColor both changes the color and also changes toggle.
Here's a step-by-step:
1. toggle==0 at the beginning of the ap
2. mouse enters rect and changeColor is called.
3. changeColor changes color to #ffffff because toggle==0.
4. changeColor changes toggle=1
5. mouse exits rect
6. mouse enters rect again and changeColor is called again.
7. changeColor changes color to #04b45f because toggle==1.
8. changeColor changes toggle=0;
mouseover will only know when you're over the canvas, so you need to detect you're above the square (I'm using the variables already defined by you):
var sqx1 = c.offsetLeft + 150; //left top corner of the square respect to the window
var sqy1 = c.offsetTop + 100;
var sqx2 = sqx1 + 100; //right bottom corner of the square respect to the window
var sqy2 = sqy1 + 100;
var lastOverSquare = false;
c.addEventListener('mousemove', function(e) {
var overSquare =
(sqx1 <= e.pageX && sqx2 >= e.pageX) &&
(sqy1 <= e.pageY && sqy2 >= e.pageY);
if (overSquare && !lastOverSquare) changeColour(); //change only when it enters the square, not every move when we're already over it.
lastOverSquare = overSquare;
}, false);
var colours = ['#FFFFFF', '#04B45F'];
var currentColour = 0;
ctx.fillStyle = colours[currentColour];
function changeColour() {
currentColour = (currentColour + 1) % colours.length;
ctx.fillStyle = colours[currentColour];
}
Please, may someone help me! I am new in javascript.
I want to make canvas animation using javascript. But I have the following error
SCRIPT5007: Unable to get value of the property 'getContext': object
is null or undefined drawing_script.js, line 31 character 5
Here is the code.
Javascript:
// JScript source code
/*
Because the canvas can hold only one context at time, we'll create two canvas. Each one with its context.
One canvas for the circle, and another one for the square.
*/
var canvasCircle;
var contextCircle;
var x = 400;
var y = 300;
var dx = 2;
var WIDTH = 800;
var HEIGHT = 600;
// the circle wont make any transsformation.
function draw_circle(x, y, r) {
contextCircle.beginPath();
contextCircle.arc(x, y, r, 0, 2 * Math.PI, true);
contextCircle.closePath();
contextCircle.stroke();
}
function clear_canvas() {
contextCircle.clearRect(0, 0, WIDTH, HEIGHT);
}
function init() {
//canvasCircle = document.getElementById("canvas_circle");
canvasCircle = document.getElementById("canvas_circle");
contextCircle = canvasCircle.getContext('2d');
return setInterval(draw, 10);
}
function draw() {
// clear_canvas();
draw_circle(x, y, 50);
// if (x + dx > WIDTH || x + dx < 0)
// dx = -dx;
// x += dx;
}
init();
HTML5:
<!DOCTYPE HTML>
<html>
<head>
<meta charset="UTF-8" />
<script type="text/javascript" src="Scripts/drawing_script.js" language="javascript"></script>
<title>Blackberry</title>
</head>
<body>
<div class="drawing" style="background:Green">
<canvas id="canvas_circle" width="800" height="600"></canvas>
This is happening because your executing the script before you create the canvas.
Create the canvas element FIRST then embed the javascript.
IE: canvasCircle is undefined because you can't get an element by ID that does not exist yet!
I found the answer: the init() should be
function init() {
s_canvas = document.getElementById("canvas_square");
// Check if the canvas is supported and if the getContext is available
if (s_canvas && s_canvas.getContext) {
s_context = s_canvas.getContext("2d");
return setInterval(draw, 10);
}
else {
alert("Canvas is not supported!");
}
}
And the called of init() is replace with window.onload=init.
Since you said that you are new to javascript, I believe that the problem could be that the browser on which you are running the code may not be supporting canvas.