javascript 如何使用html5中的键盘箭头键在画布上移动图像
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how to move an image on canvas using keyboard arrow key in html5
提问by deve1
I m Drawing the image on canvas with this code and it successfully draw the image on canvas now i want to move the image on canvas for that i write the code i check that if the right key of my keyboard is pressed i will increment the x coordinate of an image if left key is pressed i will decrement the x coordinate but image is not moving on the canvas
我正在使用此代码在画布上绘制图像并且它成功地在画布上绘制图像现在我想在画布上移动图像为此我编写代码我检查是否按下键盘的右键我将增加 x如果按下左键，图像的坐标我将减少 x 坐标，但图像不会在画布上移动
player = new Image();
player.src = "game_character.png";
context.drawImage(player,player.x * wallDim + wallDim ,player.y * wallDim + wallDim ,50,50);
how to move an image on canvas
如何在画布上移动图像
var handleInput = function(event, keyState) {
switch(event.which) {
case 37: { // Left Arrow
keyDown.arrowLeft = keyState;
break;
}
case 38: { // Up Arrow
keyDown.arrowUp = keyState;
break;
}
case 39: { // Right Arrow
keyDown.arrowRight = keyState;
break;
}
case 40: { // Down Arrow
keyDown.arrowDown = keyState;
break;
}
}
}
/**
* physics
*
* This function contains the basic logic for the maze.
*/
var physics = function() {
console.log("physics ");
console.log("first condition "+keyDown.arrowRight +player.x+1);
if(keyDown.arrowLeft && player.x-1 >= 0 && map[player.y][player.x-1] != 1) {
player.x--;
redraw = true;
}
if(keyDown.arrowUp && player.y-1 >= 0 && map[player.y-1][player.x] != 1) {
player.y--;
redraw = true;
}
if(keyDown.arrowRight && player.x+1 < map[0].length && map[player.y][player.x+1] != 1) {
console.log("arrow right");
player.x++;
redraw = true;
}
if(keyDown.arrowDown && player.y+1 < map.length && map[player.y+1][player.x] != 1) {
player.y++;
redraw = true;
}
if(keyDown.arrowRight && player.x+1 >= map[0].length)
{
player.x++;
document.getElementById("canvas_div").style.display="none";
document.getElementById("end_screen_div").style.display="block";
//alert("completed");
}
}
/**
* draw
*
* This function simply draws the current state of the game.
*/
var draw = function() {
// Don't redraw if nothing has changed
if(!redraw)
return;
context.clearRect(0, 0, cols, rows);
context.beginPath();
// Draw the maze
for(var a = 0; a < rows; a++) {
for(var b = 0; b < cols; b++) {
switch(map[a][b]) {
case C.EMPTY: context.fillStyle = colors.empty; break;
case C.WALL: context.fillStyle = colors.wall; break;
}
context.fillRect(b * wallDim, a * wallDim, wallDim, wallDim); // x, y, width, height
}
}
// Draw the player
/* context.fillStyle = colors.player;
context.arc(
player.x * wallDim + wallDim / 2, // x position
player.y * wallDim + wallDim / 2, // y position
wallDim / 2, // Radius
0, // Starting angle
Math.PI * 2, // Ending angle
true // antiClockwise
);*/
player = new Image();
player.src = "game_character.png";
context.drawImage(player,player.x * wallDim + wallDim ,player.y * wallDim + wallDim ,50,50);
var firstplayer=new Image();
firstplayer.src="top_character01.png";
context.drawImage(firstplayer,680,0,60,60);
var secondplayer= new Image();
secondplayer.src="top_character02.png";
context.drawImage(secondplayer,750,0,60,60);
context.fill();
context.closePath();
redraw = false;
}
采纳答案by Denys Séguret
In your draw method, you reinitialize the player each time :
在您的 draw 方法中，您每次都重新初始化播放器：
player = new Image();
player.src = "game_character.png";
So you erase the player.x modified by your event handler.
因此，您删除了由事件处理程序修改的 player.x。
You should initialize the player only once, outside the draw function. You can move the initialization like this :
在 draw 函数之外，您应该只初始化播放器一次。您可以像这样移动初始化：
var player = new Image();
player.src = "game_character.png";
var draw = function() {
There is absolutely no need to call player.src = "game_character.png";inside the draw function.
绝对不需要player.src = "game_character.png";在 draw 函数内部调用。
As a general rule, when dealing with animation, try to remove all what you can from the draw function, which should be as fast as possible.
作为一般规则，在处理动画时，尽量从 draw 函数中删除所有可以删除的内容，这应该尽可能快。
回答by starbeamrainbowlabs
You will need to redraw the canvas each time. Something like this:
您每次都需要重新绘制画布。像这样的东西：
function init()
{
canvas = document.getElementById("canvas");
context = canvas.getContext("2d");
x = canvas.width / 2; //align to centre of the screen
y = canvas.height / 2; //same as above
speed = 5; //speed for the player to move at
width = 50; //width of the player
height = 50; //height of the player
playerimage = new Image();
playerimage.src = "path/to/image/for/player"; //path to the image to use for the player
canvas.addEventListener("keypress", update);
}
function update(event)
{
if (event.keyCode == 38)
{
y -= speed; //going up
}
if (event.keyCode == 40)
{
y += speed; //going down
}
if (event.keyCode == 37)
{
x -= speed; //going left
}
if (event.keyCode == 39)
{
x += speed; //going right
}
render();
}
function render()
{
context.clearRect(0, 0, canvas.width, canvas.height);
context.drawImage(playerimage, x, y, width, height);
}
I haven't tested it, so I don't know whether it works and there may be some mistakes here and there. It should work though! If nothing else, it will (hopefully) give you an idea of one way in which you can go about doing it...
我没有测试过，所以我不知道它是否有效，可能这里那里有一些错误。不过应该可以用！如果不出意外，它会（希望）让您了解一种可以着手去做的方法......
