我目前正在使用HTML5 Canvas和JavaScript制作弹球游戏。现在，我逐渐陷入逐像素碰撞的困境，这是因为脚蹼的基础。
现在我的Bounding Box Collision似乎正在运作
checkCollision(element) {
if (this.checkCollisionBoundingBox(element)) {
console.log("colision with the element bounding box");
if (this.checkCollisionPixelByPixel(element)) {
return true;
} else {
return false;
}
} else {
return false;
}
}
checkCollisionBoundingBox(element) {
if (this.pos.x < element.pos.x + element.width && this.pos.x + this.width > element.pos.x && this.pos.y < element.pos.y + element.height && this.pos.y + this.height > element.pos.y) {
return true;
} else {
return false;
}
}
我已经尝试了几种逐像素实现的方法但由于某种原因它不能完美地工作（在墙上，图像上，精灵上等）。我会把他们留在这里：
checkCollisionPixelByPixel(element) {
var x_left = Math.floor(Math.max(this.pos.x, element.pos.x));
var x_right = Math.floor(Math.min(this.pos.x + this.width, element.pos.x + element.width));
var y_top = Math.floor(Math.max(this.pos.y, element.pos.y));
var y_bottom = Math.floor(Math.min(this.pos.y + this.height, element.pos.y + element.height));
for (var y = y_top; y < y_bottom; y++) {
for (var x = x_left; x < x_right; x++) {
var x_0 = Math.round(x - this.pos.x);
var y_0 = Math.round(y - this.pos.y);
var n_pix = y_0 * (this.width * this.total) + (this.width * (this.actual-1)) + x_0; //n pixel to check
var pix_op = this.imgData.data[4 * n_pix + 3]; //opacity (R G B A)
var element_x_0 = Math.round(x - element.pos.x);
var element_y_0 = Math.round(y - element.pos.y);
var element_n_pix = element_y_0 * (element.width * element.total) + (element.width * (element.actual-1)) + element_x_0; //n pixel to check
var element_pix_op = element.imgData.data[4 * element_n_pix + 3]; //opacity (R G B A)
console.log(element_pix_op);
if (pix_op == 255 && element_pix_op == 255) {
console.log("Colision pixel by pixel");
/*Debug*/
/*console.log("This -> (R:" + this.imgData.data[4 * n_pix] + ", G:" + this.imgData.data[4 * n_pix + 1] + ", B:" + this.imgData.data[4 * n_pix + 2] + ", A:" + pix_op + ")");
console.log("Element -> (R:" + element.imgData.data[4 * element_n_pix] + ", G:" + element.imgData.data[4 * element_n_pix + 1] + ", B:" + element.imgData.data[4 * element_n_pix + 2] + ", A:" + element_pix_op + ")");
console.log("Collision -> (x:" + x + ", y:" + y +")");
console.log("This(Local) -> (x:" + x_0 + ", y:" + y_0+")");
console.log("Element(Local) -> (x:" + element_x_0 + ", y:" + element_y_0+")");*/
/*ball vector*/
var vector = {
x: (x_0 - Math.floor(this.imgData.width / 2)),
y: -(y_0 - Math.floor(this.imgData.height / 2))
};
//console.log("ball vector -> ("+vector.x+", "+vector.y+") , Angulo: "+ Math.atan(vector.y/vector.x)* 180/Math.PI);
// THIS WAS THE FIRST TRY, IT DIDN'T WORK WHEN THE BALL WAS GOING NORTHEAST AND COLLIDED WITH A WALL. DIDN'T WORK AT ALL WITH SPRITES
//this.angle = (Math.atan2(vector.y, vector.x) - Math.PI) * (180 / Math.PI);
// THIS WAS THE SECOND ATTEMPT, WORKS WORSE THAN THE FIRST ONE :/
//normal vector
var normal = {
x: (x_0 - (this.imgData.width / 2)),
y: -(y_0 - (this.imgData.height / 2))
};
//Normalizar o vetor
var norm = Math.sqrt(normal.x * normal.x + normal.y * normal.y);
if (norm != 0) {
normal.x = normal.x / norm;
normal.y = normal.y / norm;
}
var n_rad = Math.atan2(normal.y, normal.x);
var n_deg = (n_rad + Math.PI) * 180 / Math.PI;
console.log("Vetor Normal -> (" + normal.x + ", " + normal.y + ") , Angulo: " + n_deg);
//Vetor Velocidade
var velocity = {
x: Math.cos((this.angle * Math.PI / 180) - Math.PI),
y: Math.sin((this.angle * Math.PI / 180) - Math.PI)
};
console.log("Vetor Velocidade -> (" + velocity.x + ", " + velocity.y + ") , Angulo: " + this.angle);
//Vetor Reflexao
var ndotv = normal.x * velocity.x + normal.y * velocity.y;
var reflection = {
x: -2 * ndotv * normal.x + velocity.x,
y: -2 * ndotv * normal.y + velocity.y
};
var r_rad = Math.atan2(reflection.y, reflection.x);
var r_deg = (r_rad + Math.PI) * 180 / Math.PI;
console.log("Vetor Reflexao -> (" + reflection.x + ", " + reflection.y + ") , Angulo: " + r_deg);
this.angle = r_deg;
return true;
}
}
}
return false;
}
}
球类
class Ball extends Element {
constructor(img, pos, width, height, n, sound, angle, speed) {
super(img, pos, width, height, n, sound);
this.angle = angle; //direction [0:360[
this.speed = speed;
}
move(ctx, cw, ch) {
var rads = this.angle * Math.PI / 180
var vx = Math.cos(rads) * this.speed / 60;
var vy = Math.sin(rads) * this.speed / 60;
this.pos.x += vx;
this.pos.y -= vy;
ctx.clearRect(0, 0, cw, ch);
this.draw(ctx, 1);
}
}
答案 0 :(得分：1)
假设“鳍状肢”由2个弧和2个线组成，则数学上进行碰撞检测要快得多，而不是通过慢得多的像素测试方法。那你只需要4次数学碰撞测试。
即使你的脚蹼比弧线+线条复杂一点，数学命中测试也会“足够好” - 这意味着在快速移动的游戏中，用户无法在视觉上注意到与像素相比的近似数学结果完美的结果和两种测试之间的差异根本不会影响游戏玩法。但是像素测试版需要花费更多的时间和资源来完成。 ; - ）
前两个圆圈与圆圈的碰撞测试：
function CirclesColliding(c1,c2){
var dx=c2.x-c1.x;
var dy=c2.y-c1.y;
var rSum=c1.r+c2.r;
return(dx*dx+dy*dy<=rSum*rSum);
}
然后进行两次圆 - 线 - 线段碰撞测试：
// [x0,y0] to [x1,y1] define a line segment
// [cx,cy] is circle centerpoint, cr is circle radius
function isCircleSegmentColliding(x0,y0,x1,y1,cx,cy,cr){
// calc delta distance: source point to line start
var dx=cx-x0;
var dy=cy-y0;
// calc delta distance: line start to end
var dxx=x1-x0;
var dyy=y1-y0;
// Calc position on line normalized between 0.00 & 1.00
// == dot product divided by delta line distances squared
var t=(dx*dxx+dy*dyy)/(dxx*dxx+dyy*dyy);
// calc nearest pt on line
var x=x0+dxx*t;
var y=y0+dyy*t;
// clamp results to being on the segment
if(t<0){x=x0;y=y0;}
if(t>1){x=x1;y=y1;}
return( (cx-x)*(cx-x)+(cy-y)*(cy-y) < cr*cr );
}