实现平稳草图和绘图元件(Implementing smooth sketching and

我试图创建一个帆布绘图区域。我有使线条看起来光滑绘制曲线的时候，我也有我的算法很糟糕，以及由于尺寸跳到多好，你能看到的大小变化改变线宽的麻烦。我没有找到这对计算器的链接，但是这是对原生iPhone应用程序，我无法弄清楚。

这是我目前的JS代码。这里是它运行上的jsfiddle

var xStart,
xEnd,
yStart,
yEnd,
paint,
ctx;
$(document).ready(function (){

   ctx = $('canvas')[0].getContext("2d");
   ctx.strokeStyle = '#000';
   ctx.lineJoin="round";
   ctx.lineCap="round";
   ctx.lineWidth = 1;


   $('canvas').bind('mousedown mousemove mouseup mouseleave touchstart touchmove touchend', function(e){
        var orig = e.originalEvent;

        if(e.type == 'mousedown'){
            e.preventDefault(); e.stopPropagation();

            xStart = e.clientX - $(this).offset().left;
            yStart = e.clientY - $(this).offset().top;
            xEnd = xStart;
            yEnd = yStart;

            paint = true;
            draw(e.type);

        }else if(e.type == 'mousemove'){
            if(paint==true){
                xEnd = e.clientX - $(this).offset().left;
                yEnd = e.clientY - $(this).offset().top;


               lineThickness = 1 + Math.sqrt((xStart - xEnd) *(xStart-xEnd) + (yStart - yEnd) * (yStart-yEnd))/5;

               if(lineThickness > 10){
                    lineThickness = 10;   
               }

                ctx.lineWidth = lineThickness;
                draw(e.type);
            }
        }else if(e.type == 'mouseup'){
            paint = false;
        }else if(e.type == 'mouseleave'){
            paint = false;
        }else if(e.type == 'touchstart'){
            if(orig.touches.length == 1){
                e.preventDefault(); e.stopPropagation();

                xStart = orig.changedTouches[0].pageX - $(this).offset().left;
                yStart = orig.changedTouches[0].pageY - $(this).offset().top;
                xEnd = xStart;
                yEnd = yStart; 

                paint = true;
                draw(e.type);
            }
        }else if(e.type == 'touchmove'){
            if(orig.touches.length == 1){
                if(paint==true){
                    xEnd = orig.changedTouches[0].pageX - $(this).offset().left;
                    yEnd = orig.changedTouches[0].pageY - $(this).offset().top;


                            lineThickness = 1 + Math.sqrt((xStart - xEnd) *(xStart-xEnd) + (yStart - yEnd) * (yStart-yEnd))/6;
                       if(lineThickness > 10){
                          lineThickness = 10;   
                       }


                      ctx.lineWidth = lineThickness;


                    draw(e.type);
                }
            }
        }else if(e.type == 'touchend'){
            paint = false;
        }

      });
    });


    function draw(event){

    if(event == 'mousedown'){
        ctx.beginPath();
        ctx.moveTo(xStart, yStart);
        ctx.lineTo(xEnd, yEnd);
        ctx.stroke();
    }else if(event == 'mousemove'){
        ctx.beginPath();
        ctx.moveTo(xStart, yStart);
        ctx.lineTo(xEnd, yEnd);
        ctx.stroke();
    }else if(event == 'touchstart'){
        ctx.beginPath();
        ctx.moveTo(xStart, yStart);
        ctx.lineTo(xEnd, yEnd);
        ctx.stroke();
    }else if(event == 'touchmove'){
        ctx.beginPath();
        ctx.moveTo(xStart, yStart);
        ctx.lineTo(xEnd, yEnd);
        ctx.stroke();
    }
    xStart = xEnd;
    yStart = yEnd;                  
}

谢谢大家。

这是它看起来像现在如果你画。

......这就是我喜欢来实现：

Answer 1:

我做了这样的事情在不久前，把它变成一个jQuery插件。看看在这里，如果这是你以后我会发布一个更详细的解答，并挖掘出从我的档案简化的jQuery版本：

http://jsfiddle.net/95tft/

编辑

好吧，抱歉，我不能这样做的昨天：

原来上面的代码是从杜布先生的“和谐”草绘在这里分叉： http://mrdoob.com/projects/harmony/#ribbon

（我认为这是最好的解决方案）。但我有点打破了下来，并重拍它的另一个项目我自己的目的。我砍死我自己的插件了一下，使其更容易一点还是在这里：

http://jsfiddle.net/dh3bj/

你可能想改变的唯一的事情就是改变它在鼠标按下/鼠标松开这应该是很容易也看看在插件的底部设置的工作，你应该能够通过与打得到你想要的效果刷大小，颜色，α（RGBA）等

希望帮助

Answer 2:

看看下面的代码：

http://jsfiddle.net/aMmVQ/

我在做什么的起点上鼠标按下一个新的列表，然后为每个鼠标移动我补充一点到列表中。一旦我得到足够的积分（6左右），我开始绘制二次曲线，该曲线是当前点的平均值和下一个点的控制点。

drawPoints的是，这工作魔位：

function drawPoints(ctx, points) {
    // draw a basic circle instead
    if (points.length < 6) {
        var b = points[0];
        ctx.beginPath(), ctx.arc(b.x, b.y, ctx.lineWidth / 2, 0, Math.PI * 2, !0), ctx.closePath(), ctx.fill();
        return
    }
    ctx.beginPath(), ctx.moveTo(points[0].x, points[0].y);
    // draw a bunch of quadratics, using the average of two points as the control point
    for (i = 1; i < points.length - 2; i++) {
        var c = (points[i].x + points[i + 1].x) / 2,
            d = (points[i].y + points[i + 1].y) / 2;
        ctx.quadraticCurveTo(points[i].x, points[i].y, c, d)
    }
    ctx.quadraticCurveTo(points[i].x, points[i].y, points[i + 1].x, points[i + 1].y), ctx.stroke()
}

Answer 3:

你为什么不使用croquis.js ？

它有着简洁的刷实施，如Photoshop :)

这里是演示其使用croquis.js。

Answer 4:

看来，你需要在你的画布使用一些笔刷。很难说究竟需要什么样的刷的，但有一个已经实现刷技术很多JS库。

比如你看这个库？

Processing.js
HTML5的画布，画笔，素描（演示和文章它是如何工作）

拉索在网上，你可以找到在杜布先生实施了许多画笔和谐工程。例如粘性或和谐，刷在github上的项目。

Answer 5:

建议呈现与贝塞尔曲线包围从而其填充曲线的链来完成。（即ctx.fill结束）还有很多工作要做，但希望这有助于。

适用于Bezier曲线一个很好的演示应用程序

把它添加到你的提琴的叉http://jsfiddle.net/d3zFU/1/

码是

/*
 * Canvas curves example
 *
 * By Craig Buckler,        http://twitter.com/craigbuckler
 * of OptimalWorks.net        http://optimalworks.net/
 * for SitePoint.com        http://sitepoint.com/
 *
 * Refer to:
 * http://blogs.sitepoint.com/html5-canvas-draw-quadratic-curves/
 * http://blogs.sitepoint.com/html5-canvas-draw-bezier-curves/
 *
 * This code can be used without restriction.
 */

（函数（）{

var canvas, ctx, code, point, style, drag = null, dPoint;

// define initial points
function Init(quadratic) {

    point = {
        p1: { x:100, y:250 },
        p2: { x:400, y:250 }
    };

    if (quadratic) {
        point.cp1 = { x: 250, y: 100 };
    }
    else {
        point.cp1 = { x: 150, y: 100 };
        point.cp2 = { x: 350, y: 100 };
    }

    // default styles
    style = {
        curve:    { width: 6, color: "#333" },
        cpline:    { width: 1, color: "#C00" },
        point: { radius: 10, width: 2, color: "#900", fill: "rgba(200,200,200,0.5)", arc1: 0, arc2: 2 * Math.PI }
    }

    // line style defaults
    ctx.lineCap = "round";
    ctx.lineJoin = "round";

    // event handlers
    canvas.onmousedown = DragStart;
    canvas.onmousemove = Dragging;
    canvas.onmouseup = canvas.onmouseout = DragEnd;

    DrawCanvas();
}


// draw canvas
function DrawCanvas() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);

    // control lines
    ctx.lineWidth = style.cpline.width;
    ctx.strokeStyle = style.cpline.color;
    ctx.fillStyle = style.cpline.color;
    ctx.beginPath();
    ctx.moveTo(point.p1.x, point.p1.y);
    ctx.lineTo(point.cp1.x, point.cp1.y);
    if (point.cp2) {
        ctx.moveTo(point.p2.x, point.p2.y);
        ctx.lineTo(point.cp2.x, point.cp2.y);
    }
    else {
        ctx.lineTo(point.p2.x, point.p2.y);
    }
    ctx.stroke();

    // curve
ctx.lineWidth = 1 ; //style.curve.width;
    ctx.strokeStyle = style.curve.color;
    ctx.beginPath();
    ctx.moveTo(point.p1.x, point.p1.y);
    if (point.cp2) {
        ctx.bezierCurveTo(point.cp1.x, point.cp1.y, point.cp2.x, point.cp2.y, point.p2.x, point.p2.y);
        ctx.bezierCurveTo(point.cp2.x, point.cp2.y+12, point.cp1.x, point.cp1.y+12, point.p1.x, point.p1.y);

    }
    else {
        ctx.quadraticCurveTo(point.cp1.x, point.cp1.y, point.p2.x, point.p2.y);
    }
//ctx.stroke();
ctx.fill();

    // control points
    for (var p in point) {
        ctx.lineWidth = style.point.width;
        ctx.strokeStyle = style.point.color;
        ctx.fillStyle = style.point.fill;
        ctx.beginPath();
        ctx.arc(point[p].x, point[p].y, style.point.radius, style.point.arc1, style.point.arc2, true);
        ctx.fill();
        ctx.stroke();
    }

    ShowCode();
}


// show canvas code
function ShowCode() {
    if (code) {
        code.firstChild.nodeValue =
            "canvas = document.getElementById(\"canvas\");\n"+
            "ctx = canvas.getContext(\"2d\")\n"+
            "ctx.lineWidth = " + style.curve.width +
            ";\nctx.strokeStyle = \"" + style.curve.color +
            "\";\nctx.beginPath();\n" +
            "ctx.moveTo(" + point.p1.x + ", " + point.p1.y +");\n" +
            (point.cp2 ?
                "ctx.bezierCurveTo("+point.cp1.x+", "+point.cp1.y+", "+point.cp2.x+", "+point.cp2.y+", "+point.p2.x+", "+point.p2.y+");" :
                "ctx.quadraticCurveTo("+point.cp1.x+", "+point.cp1.y+", "+point.p2.x+", "+point.p2.y+");"
            ) +
            "\nctx.stroke();"
        ;
    }
}


// start dragging
function DragStart(e) {
    e = MousePos(e);
    var dx, dy;
    for (var p in point) {
        dx = point[p].x - e.x;
        dy = point[p].y - e.y;
        if ((dx * dx) + (dy * dy) < style.point.radius * style.point.radius) {
            drag = p;
            dPoint = e;
            canvas.style.cursor = "move";
            return;
        }
    }
}


// dragging
function Dragging(e) {
    if (drag) {
        e = MousePos(e);
        point[drag].x += e.x - dPoint.x;
        point[drag].y += e.y - dPoint.y;
        dPoint = e;
        DrawCanvas();
    }
}


// end dragging
function DragEnd(e) {
    drag = null;
    canvas.style.cursor = "default";
    DrawCanvas();
}


// event parser
function MousePos(event) {
    event = (event ? event : window.event);
    return {
        x: event.pageX - canvas.offsetLeft,
        y: event.pageY - canvas.offsetTop
    }
}


// start
canvas = document.getElementById("canvas");
code = document.getElementById("code");
if (canvas.getContext) {
    ctx = canvas.getContext("2d");
    Init(canvas.className == "quadratic");
}

}）（）;