重繪帆布HTML5無閃爍

Question

我有一個畫面是重繪每25毫秒，並且圖像閃爍，這裏是我的代碼

   var FRAME_RATE = 40; 
       var intervalTime = 1000/FRAME_RATE; 
       gameLoop(); 

       function gameLoop(){ 
        context.clearRect(0, 0, 640, 640); 
        renderMap(); 
        window.setTimeout(gameLoop, intervalTime); 
       } 

，這裏是renderMap（）函數

function renderMap(){ 
        var startX = playerX - (screenW/2); 
        var startY = playerY - (screenH/2); 

        maxX = playerX + (screenW/2); 
        maxY = playerY + (screenH/2); 
        $.getJSON('mapa3.json', function(json){ 
         for (x = startX; x < maxX; x=x+32){ 
          for (y = startY; y < maxY; y=y+32){ 
           intTile = json.layers[0].data[((y/32)* 100) + (x/32)]; 
           context.putImageData(getTile(intTile - 1), x - startX, y - startY); 
          } 
         } 
        }); 

        var imgCharacter = new Image(); 
        imgCharacter.src = 'char.png'; 

        var posX = (screenW - imgCharacter.width)/2; 
        var posY = (screenH - imgCharacter.height)/2; 
        imgCharacter.onload = function(){context.drawImage(imgCharacter, posX, posY)}  
       } 

哪些變化我是否需要對代碼進行停止閃爍？

Answer 1

我相信這是因爲你每次迭代都要加載圖像。嘗試把var imgCharacter...，下面一行，並renderMap外樹形象的onload功能，所以它是隻跑了一次

var imgCharacter = new Image();  
imgCharacter.onload = function() { 
    renderMap(); 
} 
imgCharacter.src = 'char.png'; 

function renderMap() { 
    var startX = playerX - (screenW/2); 
    var startY = playerY - (screenH/2); 

    maxX = playerX + (screenW/2); 
    maxY = playerY + (screenH/2); 
    $.getJSON('mapa3.json', function (json) { 
     for (x = startX; x < maxX; x = x + 32) { 
      for (y = startY; y < maxY; y = y + 32) { 
       intTile = json.layers[0].data[((y/32) * 100) + (x/32)]; 
       context.putImageData(getTile(intTile - 1), x - startX, y - startY); 
      } 
     } 
    }); 

    var posX = (screenW - imgCharacter.width)/2; 
    var posY = (screenH - imgCharacter.height)/2; 

    context.drawImage(imgCharacter, posX, posY) 
} 

謝謝坊間讓我知道onload功能也需要到外面去renderMap，我忽略它是第一次

Answer 2

加載所有的圖像和其他數據之前繪製和存儲在陣列內。
更好地使用requestAnimationFrame。請記住，獲取JSON（或其他數據）可能需要一些時間。