问题
Is it possible to create small animated footsteps in HTML SVG or Canvas. I am just starting out with these technologies, and it is very much necessary for a small project i am working on.
My current idea was to create and use a "gif" of animated footsteps. But i would like to know if it can be achieved in any other way through HTML/CSS/JS
PS : The footsteps i keep mentioning should be similar to the footsteps that appear on the "Marauders Map" in harry potter Movies.
Thanks for any help
回答1:
Walk about.
I have never seen the movie you talk about so I am guessing what you are after.
To do it on the canvas is easy, and I am more than happy to write an example of how it's done for you.
Draw a foot
You need an image of a foot, or some way to draw a foot. I used a set of shapes I happened to have to draw a foot.
Then create a function that draws the foot at a location and in a direction. You also need to specify if its a left or right step.
If you have a foot image you want to use just replace the code in the drawFoot function after the comment // draw the foot... with ctx.drawImage(footImage,-footImage.width / 2, -footImage.height / 2);
You may have to scale the image, and the foot image should be of the left foot toes pointing to the right of screen
Path
The path to walk along is just an array of points, [x,y,x,y...] in order that define the path to travel along, They are just a guide as each foot step is a fixed distance apart and the points can be any distance appart.
Animate
Each step is some time apart (demo is 500ms or half a second). I use setTimeout to call the function to draw the next step. When the function is called I find the next position on the path and draw the next foot step.
When the walk has gone past the end of the path I clear the canvas and restart.
Demo
It's self explanatory in the demo. I track two positions on the path, one is where the foot step is, and the other is just ahead and used to get the direction the foot should be drawn.
The function that gets the distance along the path is recursive because the path points are not uniform in distance apart, so may have to skip line segments if the distance to travel is greater than the current or next or few line segments.
// create a canvas and add it to the DOM
var createImage=function(w,h){var i=document.createElement("canvas");i.width=w;i.height=h;i.ctx=i.getContext("2d");return i;}
var canvas = createImage(1024,512);
var ctx = canvas.ctx;
document.body.appendChild(canvas);
// shapes for the foot. Left foot
const foot = [
[50.86759744022923,-21.798383338076917,54.16000854997335,-23.917474843549847,57.778065334829385,-25.310771525314685,61.579706305344985,-24.823762596975733,65.0168431653022,-22.69100336700319,65.22736925598322,-19.777045647294724,63.09649708656406,-16.826669881834157,59.66512409715465,-15.356252875428147,56.12216018899968,-14.92259970211097,52.06404407417057,-16.231839553378,50.2945579442406,-18.938589556263246],
[60.12039562389232,-12.45714817900668,63.92394094034509,-14.994440399059425,68.75013312287521,-15.737202635924493,73.10937504616481,-14.878459739068003,76.36064492186433,-12.559833524837757,77.6863729180915,-9.181208344485064,75.4625672565435,-5.673231626251427,71.79886053681197,-3.7381471592011817,66.8618942467243,-3.4903609701416993,62.29264392518654,-5.1248680438596885,58.98975517513061,-8.760952968033395],
[65.57414109270752,1.1797411270282658,69.37768640916029,-1.3575510930244814,74.20387859169041,-2.1003133298895467,78.56312051498001,-1.241570433033059,81.81439039067953,1.0770557811971881,83.14011838690669,4.455680961549877,80.9163127253587,7.963657679783514,77.25260600562717,9.898742146833756,72.3156397155395,10.146528335893239,67.74638939400174,8.512021262175251,64.44350064394581,4.875936338001546],
[65.89915812212375,15.917267748549033,69.97688522977245,12.635767809535894,76.25232402290966,11.736330263416008,81.47328014710077,12.477566678331382,86.09545897877996,15.579569438835726,86.99032987455637,21.425830739951824,83.82647235747945,24.97297628549917,79.18353918133074,27.064789354098487,73.69821507617947,27.23418460503707,68.46309469655478,24.972976285499172,64.88602415530316,20.55351481505123],
[58.48881251239855,36.09589759380796,65.7080603859302,29.82038065752831,74.19222753183148,28.331948884004674,82.75081761131048,31.085582242549528,88.10923922724437,34.28575070762116,91.45825273720305,41.65358042953028,87.067323913035,47.45853718012533,79.77391671356942,50.28659303297933,71.73628428966856,50.06332546564875,64.14518700042888,47.45853718012533,60.12637078847845,42.69549574373964],
[-73.48953442580058,20.579088801900756,-80.48690958722098,13.959950657259256,-81.93681598574045,6.269142804242765,-81.49554012532147,-1.6107832746678348,-77.90207999991593,-9.181527272091415,-71.6611785393426,-14.98115303708649,-64.60076477263831,-17.880965834138024,-57.35123278004056,-19.078714598132443,-50.09111381970131,-19.902008890566687,-42.96765884171789,-19.08249722231963,-35.655087439697766,-18.51514254492067,-28.90987071615029,-18.578181953551955,-21.74774447703016,-19.60773669210723,-14.309090001741001,-20.364210136314323,-6.933479190821032,-21.688037717705875,0.33383104043200396,-22.888118253462963,7.772483543580581,-23.77067027395373,15.274173171058239,-24.338024951681817,22.460665755024706,-24.590182586206954,29.710197747622452,-23.707630865368966,36.8557533915613,-22.565778766908277,44.16832856198768,-19.28772830000901,51.48089996424725,-14.370654426435763,56.713170880643965,-7.499358885625703,60.24016927073608,-0.41616112008138906,61.75311234056134,6.518193267525415,62.38350642684393,13.515567625813127,61.67231220934209,20.50500542283382,59.08769637136125,27.56541945045329,54.35974072401175,34.87799085169213,48.686193947196124,39.41682827314464,41.87793781501736,42.379680478815025,34.313208779263185,43.26223219965301,27.063676786665432,42.25360166155246,19.625026568173826,38.28211891778152,13.457927624759604,31.720792179781256,9.486440924356895,25.290772320002496,6.019273449215143,18.7346738223298,0.21964785513691965,13.565442314564446,-5.832135373466421,9.467880753530935,-12.632472285211591,8.882365666622222,-19.188577231399584,11.277861070017005,-26.31203040678842,14.49287091019486,-32.99420772170462,17.833959567652954,-39.2981485848331,20.670732956060768,-45.854247082486715,23.192309301312157,-52.47338498877162,24.89437333435685,-59.5968381641068,25.020452151619416,-67.33461307855538,23.697386555044208],
]
const footScale = 0.2; // how big the foot is
const stepLen = 60; // distance between steps
var stepCount = 0; // current set num so left and right can be known
var stepTime = 500; // time ms between steps
// path to walk
const path = [56.20191403126277,162.4451015086347,83.38688266344644,172.80127602121507,107.98280549274708,192.86637096042372,121.57528916149568,221.34586055208607,124.81159479691195,256.2979614145819,141.64038410107662,293.8391067854107,168.82535143857336,311.9624183437419,203.77745230106916,336.5583411729056,238.0822920364817,344.9727358249879,278.2124819156436,341.0891690624884,316.40088841355566,329.43846877498976,343.58585575105235,310.6678960895754,370.77082308854904,275.7157952270795,359.12012280105046,244.64726112708325,344.23311687813566,207.10611575625444,355.23655603855093,168.9177092583423,394.0722236635463,137.2019140312628,438.0859803052077,137.84917515834604,487.27782596353507,174.0957982750084,507.9901820301992,221.9931216791693,513.1682710468652,269.243183956247,500.87030963228347,318.43502961457443,480.1579535656192,354.68165273123674,453.62744426338134,396.86543776550707,414.1445200788371,427.9340428271046,372.7198079555102,447.3518767949864,320.2916566617712,442.173787778395,272.39433325761024,427.9340429825634,218.02439858261675,441.5265266513118,185.66134222845398,472.59506075130815,160.418158272207,514.6670340117198,168.2291881671332,557.5405924870362,200.59229872785795,598.9654951914354,232.9553551615553,627.4449850627141,273.08554504131894,651.3936467669101,320.3356073183967,663.0443470544095,368.2329307225576,663.6916081814927,417.4247763808851,649.4518633856611,460.7912718954633,626.150462810664,509.33585642670744,593.1401453294179,530.6954736204549,556.8935222127556,559.9273870166451,517.9197870310509,582.4287517306153,484.11964343037323,597.1560832290169,459.03222473087396,621.0274949086466,438.11039022321154,651.3689440081158,429.43667093843567,686.3731150817684,432.05029606733103,726.1878666750503,421.6902139845064,748.5744620042316,397.8927935245363,778.6337708564557,367.5111094723503,792.6287871481064,335.0802046803193,795.4641381478963,294.8623601925252,790.3177294792127,255.26933447013639,776.3228370821212,225.344431214269,746.3711518226298,192.73203550406103,713.7991149596966,199.06094085265394,674.3068624609349,207.5062077919911,638.4763261746227,190.31310645331482,613.6509940547375,146.74931837304698,621.5992452450397,103.454341485492,665.5124383180124,60.96567428151931,716.1845355322713,48.49595708249788,763.6383682758693,51.23726133320403,810.1045243122669,71.53440096982465,842.407749982487,97.97907893142005,879.5993779794437,131.14717279570036,903.6790094213126,175.24174017377706,915.9471803279671,219.31612086267396,902.1335310600084,270.1561321514687,880.1365756762476,315.0232456643523,884.5103070340778,370.89556334366307,909.7723644212043,407.9691345807976,947.0675376346722,439.8492118274288,990.6429384281869,439.26727537005956,1036.8675099917996,414.23364852545194,1070.3264506272462,387.0500494883014,1100.6074853525497,351.4546920217324,1119.943854180156,306.7958514306488,1128.5371035594999,259.67124425611814,1122.6651029017848,208.79760059460207,1106.8898009575623,162.16340658911932,1082.4004208812885,108.81054339506417,1050.2046949092428,81.72759371897288,1016.627194271211,46.42875173061529];
const pLen = path.length;
// fix the path so it starts at zero
for(var i = 2; i < pLen; i += 2){
path[i] -= path[0];
path[i+1] -= path[1];
}
path[0] = path[1] = 0;
// tracks the foot pos
var pos = {
x : path[0],
y : path[1],
index : 0,
};
// tracks the foot pointing to pos
var pos1 = {
x : path[0],
y : path[1],
index : 0,
};
// get a distance alone the path
function getDistOnPath(dist,pos){
var nx = path[(pos.index + 2) % pLen] - pos.x;
var ny = path[(pos.index + 3) % pLen] - pos.y;
var d = Math.hypot(nx, ny);
if(d > dist){
pos.x += (nx / d) * dist;
pos.y += (ny / d) * dist;
return pos;
}
dist -= d;
pos.index += 2;
pos.x = path[pos.index % pLen];
pos.y = path[(pos.index + 1) % pLen];
return getDistOnPath(dist, pos);
}
function drawFoot(x,y,dir,left){
var i,j,shape;
var xdx = Math.cos(dir) * footScale;
var xdy = Math.sin(dir) * footScale;
if(left){
ctx.setTransform(xdx, xdy, -xdy, xdx, x + xdy * 50, y - xdx * 50);
ctx.rotate(-0.1); // make the foot turn out a bit
}else{
ctx.setTransform(xdx, xdy, -xdy, xdx, x - xdy * 50, y + xdx * 50);
ctx.rotate(-0.1); // make the foot turn out a bit
ctx.scale(1,-1); // right foot needs to be mirrored
}
// draw the foot as a set of paths points
ctx.beginPath();
for(j = 0; j < foot.length; j ++){
shape = foot[j];
i = 0;
ctx.moveTo(shape[i++],shape[i++]);
while(i < shape.length){
ctx.lineTo(shape[i++],shape[i++]);
}
ctx.closePath();
}
ctx.fill();
}
ctx.setTransform(1,0,0,1,0,0);
ctx.clearRect(0,0,canvas.width,canvas.height);
pos1 = getDistOnPath(stepLen/10,pos1); // put the second pos infront so that a direction can be found
function drawStep(){
if(pos.index > pLen){ // if past end of path clear and restart
ctx.setTransform(1,0,0,1,0,0);
ctx.clearRect(0,0,canvas.width,canvas.height);
pos.index = 0;
pos1.index = 0;
pos1.x = pos.x = path[0];
pos1.y = pos.y = path[1];
pos1 = getDistOnPath(stepLen/10,pos1);
}
pos = getDistOnPath(stepLen,pos);
pos1 = getDistOnPath(stepLen,pos1);
drawFoot(pos.x,pos.y,Math.atan2(pos1.y - pos.y, pos1.x - pos.x),(stepCount++) % 2 === 0);
setTimeout(drawStep,stepTime);
}
drawStep();Note some of the code is ES6 and will require babel (or equivilent) to run on legacy browsers.
来源：https://stackoverflow.com/questions/41653467/animated-footsteps-in-html-svg