このようなジャンプ動作が得られます (チュートリアルで同じコードを使用)
JSFiddle
var canvas;// the canvas element which will draw on
var ctx;// the "context" of the canvas that will be used (2D or 3D)
var dx = 50;// the rate of change (speed) horizontal object
var x = 30;// horizontal position of the object (with initial value)
var y = 150;// vertical position of the object (with initial value)
var limit = 10; //jump limit
var jump_y = y;
var WIDTH = 1000;// width of the rectangular area
var HEIGHT = 340;// height of the rectangular area
var tile1 = new Image ();// Image to be loaded and drawn on canvas
var posicao = 0;// display the current position of the character
var NUM_POSICOES = 6;// Number of images that make up the movement
var goingDown = false;
var jumping;
function KeyDown(evt){
switch (evt.keyCode) {
case 39: /* Arrow to the right */
if (x + dx < WIDTH){
x += dx;
posicao++;
if(posicao == NUM_POSICOES)
posicao = 1;
Update();
}
break;
case 38:
jumping = setInterval(Jump, 100);
}
}
function Draw() {
ctx.font="20px Georgia";
ctx.beginPath();
ctx.fillStyle = "red";
ctx.beginPath();
ctx.rect(x, y, 10, 10);
ctx.closePath();
ctx.fill();
console.log(posicao);
}
function LimparTela() {
ctx.fillStyle = "rgb(233,233,233)";
ctx.beginPath();
ctx.rect(0, 0, WIDTH, HEIGHT);
ctx.closePath();
ctx.fill();
}
function Update() {
LimparTela();
Draw();
}
var Jump = function(){
if(y > limit && !goingDown){
y-=10;
console.log('jumping: ' + y);
} else{
goingDown = true;
y +=10;
if(y > jump_y){
clearInterval(jumping);
goingDown = false;
}
}
}
function Start() {
canvas = document.getElementById("canvas");
ctx = canvas.getContext("2d");
return setInterval(Update, 100);
}
window.addEventListener('keydown', KeyDown);
Start();