删除或隐藏上一帧中的图像-html 5画布
Delete or hide the image in previous frame - html 5 canvas
我正在尝试使用htlm5和js编辑一个pacman实现（源代码）。问题是当我使背景透明时，重影和pacman图像保持预览帧。这是关于我的问题的一个例子。
我的js代码：
Pacman.FPS = 30;
Pacman.Ghost = function (game, map, colour) {
function getColour() {
if (eatable) {
if (secondsAgo(eatable) > 5) {
return game.getTick() % 20 > 10 ? "rgba(0, 0, 0, 0.1)" : "rgba(0, 0, 0, 0.1)";
} else {
return "rgba(0, 0, 0, 0.1)";
}
} else if(eaten) {
return "#222";
}
return colour;
};
function draw(ctx) {
var s = map.blockSize,
top = (position.y/10) * s,
left = (position.x/10) * s;
if (eatable && secondsAgo(eatable) > 8) {
eatable = null;
}
if (eaten && secondsAgo(eaten) > 3) {
eaten = null;
}
var tl = left + s;
var base = top + s - 3;
var inc = s / 10;
var high = game.getTick() % 10 > 5 ? 3 : -3;
var low = game.getTick() % 10 > 5 ? -3 : 3;
ctx.fillStyle = getColour();
ctx.beginPath();
ctx.moveTo(left, base);
ctx.quadraticCurveTo(left, top, left + (s/2), top);
ctx.quadraticCurveTo(left + s, top, left+s, base);
// Wavy things at the bottom
ctx.quadraticCurveTo(tl-(inc*1), base+high, tl - (inc * 2), base);
ctx.quadraticCurveTo(tl-(inc*3), base+low, tl - (inc * 4), base);
ctx.quadraticCurveTo(tl-(inc*5), base+high, tl - (inc * 6), base);
ctx.quadraticCurveTo(tl-(inc*7), base+low, tl - (inc * 8), base);
ctx.quadraticCurveTo(tl-(inc*9), base+high, tl - (inc * 10), base);
ctx.closePath();
ctx.fill();
ctx.beginPath();
ctx.fillStyle = "#FFF";
ctx.arc(left + 6,top + 6, s / 6, 0, 300, false);
ctx.arc((left + s) - 6,top + 6, s / 6, 0, 300, false);
ctx.closePath();
ctx.fill();
var f = s / 12;
var off = {};
off[RIGHT] = [f, 0];
off[LEFT] = [-f, 0];
off[UP] = [0, -f];
off[DOWN] = [0, f];
ctx.beginPath();
ctx.fillStyle = "rgba(0, 0, 0, 0)";
//ctx.fillStyle = "#000";
ctx.arc(left+6+off[direction][0], top+6+off[direction][3],
s / 15, 0, 300, false);
ctx.arc((left+s)-6+off[direction][0], top+6+off[direction][4],
s / 15, 0, 300, false);
ctx.closePath();
ctx.fill();
};
function pane(pos) {
if (pos.y === 100 && pos.x >= 190 && direction === RIGHT) {
return {"y": 100, "x": -10};
}
if (pos.y === 100 && pos.x <= -10 && direction === LEFT) {
return position = {"y": 100, "x": 190};
}
return false;
};
function move(ctx) {
var oldPos = position,
onGrid = onGridSquare(position),
npos = null;
if (due !== direction) {
npos = getNewCoord(due, position);
if (onGrid &&
map.isFloorSpace({
"y":pointToCoord(nextSquare(npos.y, due)),
"x":pointToCoord(nextSquare(npos.x, due))})) {
direction = due;
} else {
npos = null;
}
}
if (npos === null) {
npos = getNewCoord(direction, position);
}
if (onGrid &&
map.isWallSpace({
"y" : pointToCoord(nextSquare(npos.y, direction)),
"x" : pointToCoord(nextSquare(npos.x, direction))
})) {
due = getRandomDirection();
return move(ctx);
}
position = npos;
var tmp = pane(position);
if (tmp) {
position = tmp;
}
due = getRandomDirection();
return {
"new" : position,
"old" : oldPos
};
};
return {
"eat" : eat,
"isVunerable" : isVunerable,
"isDangerous" : isDangerous,
"makeEatable" : makeEatable,
"reset" : reset,
"move" : move,
"draw" : draw
};
};
Pacman.User = function (game, map) {
var position = null,
direction = null,
eaten = null,
due = null,
lives = null,
score = 5,
keyMap = {};
keyMap[KEY.ARROW_LEFT] = LEFT;
keyMap[KEY.ARROW_UP] = UP;
keyMap[KEY.ARROW_RIGHT] = RIGHT;
keyMap[KEY.ARROW_DOWN] = DOWN;
function addScore(nScore) {
score += nScore;
if (score >= 10000 && score - nScore < 10000) {
lives += 1;
}
};
function theScore() {
return score;
};
function loseLife() {
lives -= 1;
};
function getLives() {
return lives;
};
function initUser() {
score = 0;
lives = 3;
newLevel();
}
function newLevel() {
resetPosition();
eaten = 0;
};
function resetPosition() {
position = {"x": 90, "y": 120};
direction = LEFT;
due = LEFT;
};
function reset() {
initUser();
resetPosition();
};
function keyDown(e) {
if (typeof keyMap[e.keyCode] !== "undefined") {
due = keyMap[e.keyCode];
e.preventDefault();
e.stopPropagation();
return false;
}
return true;
};
function getNewCoord(dir, current) {
return {
"x": current.x + (dir === LEFT && -2 || dir === RIGHT && 2 || 0),
"y": current.y + (dir === DOWN && 2 || dir === UP && -2 || 0)
};
};
function onWholeSquare(x) {
return x % 10 === 0;
};
function pointToCoord(x) {
return Math.round(x/10);
};
function nextSquare(x, dir) {
var rem = x % 10;
if (rem === 0) {
return x;
} else if (dir === RIGHT || dir === DOWN) {
return x + (10 - rem);
} else {
return x - rem;
}
};
function next(pos, dir) {
return {
"y" : pointToCoord(nextSquare(pos.y, dir)),
"x" : pointToCoord(nextSquare(pos.x, dir)),
};
};
function onGridSquare(pos) {
return onWholeSquare(pos.y) && onWholeSquare(pos.x);
};
function isOnSamePlane(due, dir) {
return ((due === LEFT || due === RIGHT) &&
(dir === LEFT || dir === RIGHT)) ||
((due === UP || due === DOWN) &&
(dir === UP || dir === DOWN));
};
function move(ctx) {
var npos = null,
nextWhole = null,
oldPosition = position,
block = null;
if (due !== direction) {
npos = getNewCoord(due, position);
if (isOnSamePlane(due, direction) ||
(onGridSquare(position) &&
map.isFloorSpace(next(npos, due)))) {
direction = due;
} else {
npos = null;
}
}
if (npos === null) {
npos = getNewCoord(direction, position);
}
if (onGridSquare(position) && map.isWallSpace(next(npos, direction))) {
direction = NONE;
}
if (direction === NONE) {
return {"new" : position, "old" : position};
}
if (npos.y === 100 && npos.x >= 190 && direction === RIGHT) {
npos = {"y": 100, "x": -10};
}
if (npos.y === 100 && npos.x <= -12 && direction === LEFT) {
npos = {"y": 100, "x": 190};
}
position = npos;
nextWhole = next(position, direction);
block = map.block(nextWhole);
if ((isMidSquare(position.y) || isMidSquare(position.x)) &&
block === Pacman.BISCUIT || block === Pacman.PILL) {
map.setBlock(nextWhole, Pacman.EMPTY);
addScore((block === Pacman.BISCUIT) ? 10 : 50);
eaten += 1;
if (eaten === 182) {
game.completedLevel();
}
if (block === Pacman.PILL) {
game.eatenPill();
}
}
return {
"new" : position,
"old" : oldPosition
};
};
function isMidSquare(x) {
var rem = x % 10;
return rem > 3 || rem < 7;
};
function calcAngle(dir, pos) {
if (dir == RIGHT && (pos.x % 10 < 5)) {
return {"start":0.25, "end":1.75, "direction": false};
} else if (dir === DOWN && (pos.y % 10 < 5)) {
return {"start":0.75, "end":2.25, "direction": false};
} else if (dir === UP && (pos.y % 10 < 5)) {
return {"start":1.25, "end":1.75, "direction": true};
} else if (dir === LEFT && (pos.x % 10 < 5)) {
return {"start":0.75, "end":1.25, "direction": true};
}
return {"start":0, "end":2, "direction": false};
};
function drawDead(ctx, amount) {
var size = map.blockSize,
half = size / 2;
if (amount >= 1) {
return;
}
ctx.fillStyle = "#FFFF00";
ctx.beginPath();
ctx.moveTo(((position.x/10) * size) + half,
((position.y/10) * size) + half);
ctx.arc(((position.x/10) * size) + half,
((position.y/10) * size) + half,
half, 0, Math.PI * 2 * amount, true);
ctx.fill();
};
function draw(ctx) {
var s = map.blockSize,
angle = calcAngle(direction, position);
ctx.fillStyle = "#FFFF00";
ctx.beginPath();
ctx.moveTo(((position.x/10) * s) + s / 2,
((position.y/10) * s) + s / 2);
ctx.arc(((position.x/10) * s) + s / 2,
((position.y/10) * s) + s / 2,
s / 2, Math.PI * angle.start,
Math.PI * angle.end, angle.direction);
ctx.fill();
};
initUser();
return {
"draw" : draw,
"drawDead" : drawDead,
"loseLife" : loseLife,
"getLives" : getLives,
"score" : score,
"addScore" : addScore,
"theScore" : theScore,
"keyDown" : keyDown,
"move" : move,
"newLevel" : newLevel,
"reset" : reset,
"resetPosition" : resetPosition
};
};
Pacman.Map = function (size) {
var height = null,
width = null,
blockSize = size,
pillSize = 0,
map = null;
function withinBounds(y, x) {
return y >= 0 && y < height && x >= 0 && x < width;
}
function isWall(pos) {
return withinBounds(pos.y, pos.x) && map[pos.y][pos.x] === Pacman.WALL;
}
function isFloorSpace(pos) {
if (!withinBounds(pos.y, pos.x)) {
return false;
}
var peice = map[pos.y][pos.x];
return peice === Pacman.EMPTY ||
peice === Pacman.BISCUIT ||
peice === Pacman.PILL;
}
function drawWall(ctx) {
var i, j, p, line;
ctx.strokeStyle = "#fFF";
ctx.lineWidth = 5;
ctx.lineCap = "round";
for (i = 0; i < Pacman.WALLS.length; i += 1) {
line = Pacman.WALLS[i];
ctx.beginPath();
for (j = 0; j < line.length; j += 1) {
p = line[j];
if (p.move) {
ctx.moveTo(p.move[0] * blockSize, p.move[1] * blockSize);
} else if (p.line) {
ctx.lineTo(p.line[0] * blockSize, p.line[1] * blockSize);
} else if (p.curve) {
ctx.quadraticCurveTo(p.curve[0] * blockSize,
p.curve[1] * blockSize,
p.curve[2] * blockSize,
p.curve[3] * blockSize);
}
}
ctx.stroke();
}
}
function reset() {
map = Pacman.MAP.clone();
height = map.length;
width = map[0].length;
};
function block(pos) {
return map[pos.y][pos.x];
};
function setBlock(pos, type) {
map[pos.y][pos.x] = type;
};
function drawPills(ctx) {
if (++pillSize > 30) {
pillSize = 0;
}
for (i = 0; i < height; i += 1) {
for (j = 0; j < width; j += 1) {
if (map[i][j] === Pacman.PILL) {
ctx.beginPath();
ctx.fillStyle = "rgba(0, 0, 0, 0)";
//ctx.fillStyle = "#000";
ctx.fillRect((j * blockSize), (i * blockSize),
blockSize, blockSize);
ctx.fillStyle = "#FFF";
ctx.arc((j * blockSize) + blockSize / 2,
(i * blockSize) + blockSize / 2,
Math.abs(5 - (pillSize/3)),
0,
Math.PI * 2, false);
ctx.fill();
ctx.closePath();
}
}
}
};
function draw(ctx) {
var i, j, size = blockSize;
ctx.fillStyle = "rgba(0, 0, 0, 0)";
//ctx.fillStyle = "#000";
ctx.fillRect(0, 0, width * size, height * size);
drawWall(ctx);
for (i = 0; i < height; i += 1) {
for (j = 0; j < width; j += 1) {
drawBlock(i, j, ctx);
}
}
};
function drawBlock(y, x, ctx) {
var layout = map[y][x];
if (layout === Pacman.PILL) {
return;
}
ctx.beginPath();
if (layout === Pacman.EMPTY || layout === Pacman.BLOCK ||
layout === Pacman.BISCUIT) {
ctx.fillStyle = "rgba(0, 0, 0, 0)";
//ctx.fillStyle = "#000";
ctx.fillRect((x * blockSize), (y * blockSize),
blockSize, blockSize);
if (layout === Pacman.BISCUIT) {
ctx.fillStyle = "#FFF";
ctx.fillRect((x * blockSize) + (blockSize / 2.5),
(y * blockSize) + (blockSize / 2.5),
blockSize / 6, blockSize / 6);
}
}
ctx.closePath();
};
reset();
return {
"draw" : draw,
"drawBlock" : drawBlock,
"drawPills" : drawPills,
"block" : block,
"setBlock" : setBlock,
"reset" : reset,
"isWallSpace" : isWall,
"isFloorSpace" : isFloorSpace,
"height" : height,
"width" : width,
"blockSize" : blockSize
};
};
Pacman.Audio = function(game) {
var files = [],
endEvents = [],
progressEvents = [],
playing = [];
function load(name, path, cb) {
var f = files[name] = document.createElement("audio");
progressEvents[name] = function(event) { progress(event, name, cb); };
f.addEventListener("canplaythrough", progressEvents[name], true);
f.setAttribute("preload", "true");
f.setAttribute("autobuffer", "true");
f.setAttribute("src", path);
f.pause();
};
function progress(event, name, callback) {
if (event.loaded === event.total && typeof callback === "function") {
callback();
files[name].removeEventListener("canplaythrough",
progressEvents[name], true);
}
};
function disableSound() {
for (var i = 0; i < playing.length; i++) {
files[playing[i]].pause();
files[playing[i]].currentTime = 0;
}
playing = [];
};
function ended(name) {
var i, tmp = [], found = false;
files[name].removeEventListener("ended", endEvents[name], true);
for (i = 0; i < playing.length; i++) {
if (!found && playing[i]) {
found = true;
} else {
tmp.push(playing[i]);
}
}
playing = tmp;
};
return {
"disableSound" : disableSound,
"load" : load,
"play" : play,
"pause" : pause,
"resume" : resume
};
};
var PACMAN = (function () {
var state = WAITING,
audio = null,
ghosts = [],
ghostSpecs = ["#00FFDE", "#FF0000", "#FFB8DE", "#FFB847"],
eatenCount = 0,
level = 0,
tick = 0,
ghostPos, userPos,
stateChanged = true,
timerStart = null,
lastTime = 0,
ctx = null,
timer = null,
map = null,
user = null,
stored = null;
function getTick() {
return tick;
};
function collided(user, ghost) {
return (Math.sqrt(Math.pow(ghost.x - user.x, 2) +
Math.pow(ghost.y - user.y, 2))) < 10;
};
function drawFooter() {
var topLeft = (map.height * map.blockSize),
textBase = topLeft + 17;
ctx.fillStyle = "rgba(0, 0, 0, 0)";
//ctx.fillStyle = "#000000";
ctx.fillRect(0, topLeft, (map.width * map.blockSize), 30);
ctx.fillStyle = "rgba(0, 0, 0, 0)";
//ctx.fillStyle = "#FFFF00";
for (var i = 0, len = user.getLives(); i < len; i++) {
ctx.fillStyle = "rgba(0, 0, 0, 0)";
//ctx.fillStyle = "#FFFF00";
ctx.beginPath();
ctx.moveTo(150 + (25 * i) + map.blockSize / 2,
(topLeft+1) + map.blockSize / 2);
ctx.arc(150 + (25 * i) + map.blockSize / 2,
(topLeft+1) + map.blockSize / 2,
map.blockSize / 2, Math.PI * 0.25, Math.PI * 1.75, false);
ctx.fill();
}
ctx.fillStyle = !soundDisabled() ? "#00FF00" : "#FF0000";
ctx.font = "bold 16px sans-serif";
//ctx.fillText("♪", 10, textBase);
ctx.fillText("s", 10, textBase);
ctx.fillStyle = "#FFF";
ctx.font = "14px BDCartoonShoutRegular";
ctx.fillText("Score: " + user.theScore(), 30, textBase);
ctx.fillText("Level: " + level, 260, textBase);
}
function redrawBlock(pos) {
map.drawBlock(Math.floor(pos.y/10), Math.floor(pos.x/10), ctx);
map.drawBlock(Math.ceil(pos.y/10), Math.ceil(pos.x/10), ctx);
}
function mainDraw() {
var diff, u, i, len, nScore;
ghostPos = [];
for (i = 0, len = ghosts.length; i < len; i += 1) {
ghostPos.push(ghosts[i].move(ctx));
}
u = user.move(ctx);
for (i = 0, len = ghosts.length; i < len; i += 1) {
redrawBlock(ghostPos[i].old);
}
redrawBlock(u.old);
for (i = 0, len = ghosts.length; i < len; i += 1) {
ghosts[i].draw(ctx);
}
user.draw(ctx);
userPos = u["new"];
for (i = 0, len = ghosts.length; i < len; i += 1) {
ctx.fillStyle = "rgba(0, 0, 0, 0)";
if (collided(userPos, ghostPos[i]["new"])) {
if (ghosts[i].isVunerable()) {
audio.play("eatghost");
ghosts[i].eat();
eatenCount += 1;
nScore = eatenCount * 50;
drawScore(nScore, ghostPos[i]);
user.addScore(nScore);
setState(EATEN_PAUSE);
timerStart = tick;
} else if (ghosts[i].isDangerous()) {
audio.play("die");
setState(DYING);
timerStart = tick;
}
}
}
};
function mainLoop() {
var diff;
if (state !== PAUSE) {
++tick;
}
map.drawPills(ctx);
if (state === PLAYING) {
mainDraw();
} else if (state === WAITING && stateChanged) {
stateChanged = false;
map.draw(ctx);
dialog("Press N to start a New game");
} else if (state === EATEN_PAUSE &&
(tick - timerStart) > (Pacman.FPS / 3)) {
map.draw(ctx);
setState(PLAYING);
} else if (state === DYING) {
if (tick - timerStart > (Pacman.FPS * 2)) {
loseLife();
} else {
redrawBlock(userPos);
for (i = 0, len = ghosts.length; i < len; i += 1) {
redrawBlock(ghostPos[i].old);
//ctx.fillStyle = "rgba(0, 0, 0, 0)";
ghostPos.push(ghosts[i].draw(ctx));
}
user.drawDead(ctx, (tick - timerStart) / (Pacman.FPS * 2));
}
} else if (state === COUNTDOWN) {
diff = 5 + Math.floor((timerStart - tick) / Pacman.FPS);
if (diff === 0) {
map.draw(ctx);
setState(PLAYING);
} else {
if (diff !== lastTime) {
lastTime = diff;
map.draw(ctx);
dialog("Starting in: " + diff);
}
}
}
drawFooter();
}
}());
对于你想要制作的每一款游戏，你的gameLoop都应该包含这样的游戏逻辑（并且提前：GameAlchemist是对的，每一帧都应该重新绘制）：
- 清除整个画布
- 绘制背景元素（不要使用昂贵的调用，只需绘制一张图像。如果你有很多绘制的元素，如形状、线条等，请确保先将其缓冲在另一个隐藏的画布上）
- 如果你想的话，画更多的静态（背景）元素，它们不会改变位置（比如墙）
- 绘制动态元素（英雄、敌人、子弹等）
把所有这些步骤都想象成层（比如Photoshop），并确保按照正确的顺序进行。
这份备忘单很有用。另外，开始使用requestAnimationFrame，而不是setInterval。参见此链接。
PS请不要像你那样乞求代码。实验，尝试，失败，再试一次。然后你就会学会。而不是要求礼物包装的代码
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