Question

我用这段代码在画布上绘制图像现在我想在画布上成功绘制图像我想在画布上移动图像我编写代码我检查如果按下键盘的右键我将增加图像的x坐标如果按下左键我将递减x坐标，但图像不在画布上移动

player = new Image();
player.src = "game_character.png";
context.drawImage(player,player.x * wallDim + wallDim ,player.y * wallDim + wallDim ,50,50);

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;
  }

Answer 1

在您的绘图方法中，您每次都重新初始化播放器：

player = new Image();
player.src = "game_character.png";

因此，您删除由事件处理程序修改的player.x.

您应该只在绘图功能之外初始化播放器一次。您可以像这样移动初始化：

var player = new Image();
player.src = "game_character.png";
var draw = function() {

绝对不需要在绘制函数中调用player.src = "game_character.png";。

作为一般规则，在处理动画时，尝试从绘图功能中删除所有内容，这应该尽可能快。

Answer 2

每次都需要重绘画布。像这样：

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);
}

我没有测试过，所以我不知道它是否有效，并且可能会出现一些错误。它应该工作！如果没有别的，它（希望）会让你知道一种方法，你可以去做...

如何使用html5中的键盘箭头键在画布上移动图像

2 个答案: