Question

我在这个codePen上有一个HTML5 Canvas Spinning Cube： http://codepen.io/celli/pen/xwvnb

有人可以帮忙展示如何删除黑色背景吗？它看起来像ctx.fillStyle =＆＃34;＃000000＆＃34 ;;需要JS中的属性（尝试在CodePen中更改或删除它），但我希望有一个透明的背景，并且似乎无法找到实现这一目标的方法。

 window.onload = startDemo;

    function Point3D(x,y,z) {
        this.x = x;
        this.y = y;
        this.z = z;

        this.rotateX = function(angle) {
            var rad, cosa, sina, y, z
            rad = angle * Math.PI / 180
            cosa = Math.cos(rad)
            sina = Math.sin(rad)
            y = this.y * cosa - this.z * sina
            z = this.y * sina + this.z * cosa
            return new Point3D(this.x, y, z)
        }

        this.rotateY = function(angle) {
            var rad, cosa, sina, x, z
            rad = angle * Math.PI / 180
            cosa = Math.cos(rad)
            sina = Math.sin(rad)
            z = this.z * cosa - this.x * sina
            x = this.z * sina + this.x * cosa
            return new Point3D(x,this.y, z)
        }

        this.rotateZ = function(angle) {
            var rad, cosa, sina, x, y
            rad = angle * Math.PI / 180
            cosa = Math.cos(rad)
            sina = Math.sin(rad)
            x = this.x * cosa - this.y * sina
            y = this.x * sina + this.y * cosa
            return new Point3D(x, y, this.z)
        }

        this.project = function(viewWidth, viewHeight, fov, viewDistance) {
            var factor, x, y
            factor = fov / (viewDistance + this.z)
            x = this.x * factor + viewWidth / 2
            y = this.y * factor + viewHeight / 2
            return new Point3D(x, y, this.z)
        }
    }

    var vertices = [
        new Point3D(-1,1,-1),
        new Point3D(1,1,-1),
        new Point3D(1,-1,-1),
        new Point3D(-1,-1,-1),
        new Point3D(-1,1,1),
        new Point3D(1,1,1),
        new Point3D(1,-1,1),
        new Point3D(-1,-1,1)
    ];

    // Define the vertices that compose each of the 6 faces. These numbers are
    // indices to the vertex list defined above.
    var faces = [[0,1,2,3],[1,5,6,2],[5,4,7,6],[4,0,3,7],[0,4,5,1],[3,2,6,7]]

    var angle = 0;

    function startDemo() {
        canvas = document.getElementById("cubeSpin");
        if( canvas && canvas.getContext ) {
            ctx = canvas.getContext("2d");
            setInterval(loop,33);
        }
    }

    function loop() {
        var t = new Array();

        ctx.fillStyle="#000000";
        ctx.fillRect(0,0,320,200);

        for( var i = 0; i < vertices.length; i++ ) {
            var v = vertices[i];
            var r = v.rotateX(angle).rotateY(angle).rotateZ(angle);
            var p = r.project(320,200,128,3.5);
            t.push(p)
        }

        ctx.strokeStyle = "rgb(255,255,255)"

        for( var i = 0; i < faces.length; i++ ) {
            var f = faces[i]
            ctx.beginPath()
            ctx.moveTo(t[f[0]].x,t[f[0]].y)
            ctx.lineTo(t[f[1]].x,t[f[1]].y)
            ctx.lineTo(t[f[2]].x,t[f[2]].y)
            ctx.lineTo(t[f[3]].x,t[f[3]].y)
            ctx.closePath()
            ctx.stroke()
        }
        angle += 2

}

Answer 1

更改：

ctx.fillStyle="#FF0000"; ctx.fillRect(0,0,320,200);

要

ctx.clearRect(0,0,320,200);

帆布纺纱立方体

1 个答案: