绘画板 02——抽象并实现图形绘制功能

github 地址： https://github.com/wangyuheng/painter

DEMO 地址： http://painter.crick.wang/

针对上个版本的基础代码进行抽象和封装

将所有的图形绘制工具，都“继承”一个 DrawTool 工具类，在此工具类中绑定、解绑事件，代码如下

(function() {
	var defaultListener = {
		mousedown: function() {
			console.log('mousedown you should implement this function!');
		},
		mousemove: function() {
			console.log('mousemove you should implement this function!');
		},
		mouseup: function() {
			console.log('mouseup   you should implement this function!');
		}
	};
	var DrawTool = {
		init: function(svgDoc, listeners) {
			var l = $.extend({}, defaultListener, listeners);
			svgDoc.on('mousedown', l.mousedown);
			svgDoc.on('mousemove', l.mousemove);
			svgDoc.on('mouseup', l.mouseup);
		},
		stop: function(svgDoc, listeners) {
			var l = $.extend({}, defaultListener, listeners);
			svgDoc.off('mousemove', l.mousemove);
			svgDoc.off('mousedown', l.mousedown);
			svgDoc.off('mouseup', l.mouseup);
		}
	};


	this.DrawTool = DrawTool;
})();

所有 js 独立代码都采用闭包形式，避免的参数污染。 拆分后的目录结构如下

还是以矩形为例，Rect 在构造函数中继承使用了 DrawTool 的 init 方法，并重写 stop 方法，暴露出去。

var Rect = function(parentEle) {
    parent = parentEle;
    svgDoc = parent.doc();
    DrawTool.init(svgDoc, listener);
    this.stop = function () {
        DrawTool.stop(svgDoc, listener);
    };
};

this.DrawTool.Rect = Rect;

通过在 Rect 类内部定义 mousedown、mousemove、mouseup 事件方法，调用 svgjs 提供的绘制方法，实现图形的绘制工作。完整代码如下：

(function() {

	var parent = null;
	var drawing = false;
	var element = null;
	var startPoint = null;

	function mousedown(event) {
		console.log('rect mousedown');
		drawing = true;
		startPoint = svgDoc.transformPoint(event);
		element = parent.rect(0, 0).style("fill-opacity", '0.0').stroke({
			width: '2',
			color: '#000000'
		});
	}

	function mousemove(event) {
		console.log('rect mousemove');
		if (drawing) {
			var svgPoint = svgDoc.transformPoint(event);
			var x = svgPoint.x;
			var y = svgPoint.y;

			var newWidth = x - startPoint.x;
			var newHeight = y - startPoint.y;
			var startX = startPoint.x;
			var startY = startPoint.y;
			if (newWidth < 0) {
				startX += newWidth;
			}

			if (newHeight < 0) {
				startY += newHeight;
			}
			newWidth = Math.abs(newWidth);
			newHeight = Math.abs(newHeight);
			element.x(startX).y(startY).width(newWidth).height(newHeight);
		}
	};

	function mouseup(event) {
		console.log('rect mouseup ' + element);
		drawing = false;
	}

	var listener = {
		mousedown: mousedown,
		mousemove: mousemove,
		mouseup: mouseup,
	};


	var Rect = function(parentEle) {
		parent = parentEle;
		svgDoc = parent.doc();
		DrawTool.init(svgDoc, listener);
		this.stop = function () {
			DrawTool.stop(svgDoc, listener);
		};
	};

	this.DrawTool.Rect = Rect;

})();

有一个特殊的类为折线 polyline 工具类，此图形为连续绘制，需要记录上一个 element，并且在 stop 方法中清空之前的 element，并且监听鼠标右键点击事件，结束图形绘制。
阻止鼠标右键方法为

function mousedown(event) {
    if (event.button == 2) {
        document.oncontextmenu=function(){return false;}
        drawing=false;
        points  = [];
        element = null;
        return;
    }
    if (!drawing) {
        drawing = true;
        var currPoint = svgDoc.transformPoint(event);
        points.push([currPoint.x, currPoint.y]);
    }
}

至此，已完成图形的基本绘制功能