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[英]Why are bar graphs acting so strangely? html5 canvas, and javascript
[英]Why are the 'pixels' on my scaled HTML5 canvas strangely aligned?
我目前正在寫一些基於HTML5 canvas / JS的蛇形克隆,類似於經典的諾基亞蛇。 (這是我的第一個HTML5 canvas / JS游戲,也是我的第一個游戲,我仍然是新手程序員;))
為了簡單起見,我決定將蛇和櫻桃的每個部分都設為1像素,但是通常這會導致蛇和櫻桃非常小! ;)因此,我決定使用.scale(8,8)縮放畫布,以便每個像素為8 * 8。
var snake = {
length: 4,
direction: "right",
color: "#9A9A92",
location: [{x: 32, y: 32}, {x: 31, y: 32}, {x: 30, y: 32}, {x: 29, y: 32}]
}
var cherry = {
color: "#B1001D",
x: Math.random()*65,
y: Math.random()*65
}
var ToDrawOrNotToDraw; //limits the speed of the snake
function moveSnake(eventinfo){
if(eventinfo.keyCode === 38){
if(snake.direction === "left" || snake.direction === "right"){
snake.direction = "up";
}
}
else if(eventinfo.keyCode === 40){
if(snake.direction === "left" || snake.direction === "right"){
snake.direction = "down";
}
}
else if(eventinfo.keyCode === 37){
if(snake.direction === "up" || snake.direction === "down"){
snake.direction = "left";
}
}
else if(eventinfo.keyCode === 39){
if(snake.direction === "up" || snake.direction === "down"){
snake.direction = "right";
}
}
}
function draw(){
requestAnimationFrame(draw);
if(ToDrawOrNotToDraw === true){
var snakeDrawerCount = 0;
ctx.fillStyle = "#006C00";
ctx.fillRect(0, 0, 64, 64);
ctx.fillStyle = cherry.color;
ctx.fillRect(cherry.x, cherry.y, 1, 1);
ctx.fillStyle = snake.color;
if(snake.direction === "up"){
if(snake.location[0].y > 0){
snake.location.unshift({x: snake.location[0].x, y: snake.location[0].y-1});
snake.location.pop();
}
else {
snake.location.unshift({x: snake.location[0].x, y: 64});
snake.location.pop();
}
}
else if(snake.direction === "down"){
if(snake.location[0].y < 64){
snake.location.unshift({x: snake.location[0].x, y: snake.location[0].y+1});
snake.location.pop();
}
else {
snake.location.unshift({x: snake.location[0].x, y: 0});
snake.location.pop();
}
}
else if(snake.direction === "left"){
if(snake.location[0].x > 0){
snake.location.unshift({x: snake.location[0].x-1, y: snake.location[0].y});
snake.location.pop();
}
else {
snake.location.unshift({x: 64, y: snake.location[0].y});
snake.location.pop();
}
}
else {
if(snake.location[0].x < 64){
snake.location.unshift({x: snake.location[0].x+1, y: snake.location[0].y});
snake.location.pop();
}
else {
snake.location.unshift({x: 0, y: snake.location[0].y});
snake.location.pop();
}
}
var snakeDrawerCount = 0;
while(snakeDrawerCount < snake.location.length){
ctx.fillRect(snake.location[snakeDrawerCount].x, snake.location[snakeDrawerCount].y, 1, 1);
snakeDrawerCount++;
}
ToDrawOrNotToDraw = false;
}
else {
ToDrawOrNotToDraw = true;
}
}
var cnvs = document.getElementById("cnvs");
window.addEventListener("keydown", moveSnake, false);
var ctx = cnvs.getContext("2d");
ctx.scale(8,8); //actual size of the canvas is 512 * 512, this gives the 'pixels'/blocks on the canvas a size of 8 * 8, so the canvas will get a size of 64 * 64 'pixels'/blocks
draw();
但是出於某種奇怪的原因,那些“大像素”(8 * 8縮放像素)似乎相互重疊。 如此處所示:
不幸的是,我完全不知道為什么會這樣,因為如前所述,我對HTML5 canvas / JS還是很陌生,之前我只用Qt / QML / C ++和Python編程。 我在Firefox 26(在Linux上)和Konqueror(在KDE 4.11)(WebKit)上都試用了我的游戲,兩個瀏覽器似乎都存在問題,因此我認為這與Gecko無關。
問題來自抗鋸齒/子像素化。
您的櫻桃以隨機值放置在板上。 隨機值的問題在於它是一個浮點值,因此將Cherry偏移一些小數,因此瀏覽器將其子像素化。
當使用縮放比例時,該子像素化的結果也會被縮放(將顏色更改為例如白色時會更清楚),結果是它與網格不匹配。
為了解決這個問題,只需將cherry的x和y位置強制為整數,例如這樣:
var cherry = {
color: "#B1001D",
x: Math.random()*65|0,
y: Math.random()*65|0
}
|
是按位或運算符,它首先將數字強制為整數,以便能夠使用按位或。 由於我們對0進行OR運算,所以輸出是相同的(除了切掉浮點小數)。
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