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我在jsfiddle上创建了以下代码。目标是在单击后从画布中删除一个框。实际发生的是网格被清除并完全重新绘制，并在其旧位置删除了框。只有当所有给定的对象都被删除时，网格才会显示为空......我很困惑！我究竟做错了什么？

jQuery(function(){

    GridBox = new GridBox();

    GridBox.init();

    var canvas    = GridBox.canvas;

    canvas.on( 'click', GridBox.clickHandler );

});

function GridBox()
{

    this.target        = { x: 0, y: 0 };
    this.current       = { x: 0, y: 0 };
    this.boxHeight     = 50;
    this.boxWidth      = 50;
    this.width         = 500;
    this.height        = 500;
    this.context       = null;
    this.canvas        = null;

    var self = this,
        init = false,
        bw   = this.width,
        bh   = this.height,
        p    = 0,
        cw   = bw + ( p * 2 ) + 1,
        ch   = bh + ( p * 2 ) + 1;

    /**
     * Array of boxes that are painted on the grid.
     * Each box has its own x and y coordinates.
     */
    this.boxesOnGrid    = [
        { x: 2, y: 2 },
        { x: 9, y: 2 },
        { x: 5, y: 5 }
    ];

    /**
     * Initiate this object
     * @constructor 
     */
    this.init    = function()
    {
        if( !init ) {
            var canvas    = jQuery( '<canvas/>' ).attr({ width: cw, height: ch }).appendTo( 'body' );

            this.canvas     = canvas;
            this.context    = this.canvas.get( 0 ).getContext( '2d' );

            this.createGrid();

            init    = true;

        }
    };

    this.clearGrid        = function()
    {
        alert( 'clearing grid' );
        this.context.clearRect( 0, 0, 500, 500 );
    };

    /**
     * Create the grid 
     */
    this.createGrid        = function()
    {
        for( var x = 0; x <= bw; x += this.boxWidth ) {
            this.context.moveTo( 0.5 + x + p, p );
            this.context.lineTo( 0.5 + x + p, bh + p );
        }

        for( var x = 0; x <= bh; x += this.boxHeight ) {
            this.context.moveTo( p, 0.5 + x + p );
            this.context.lineTo( bw + p, 0.5 + x + p );
        }

        this.context.strokeStyle    = "#aaa";
        this.context.stroke();

        var boxes    = this.boxesOnGrid;

        this.boxesOnGrid    = [];

        for( key in boxes ) {
            var currentBox    = boxes[ key ];
            alert( 'i want to create box ' + currentBox.x + 'x' + currentBox.y );
            this.createBoxAt( currentBox.x, currentBox.y );
        }
    };

    /**
     * Find a suitable path between two boxes
     */
    this.findPath        = function()
    {

    };

    this.clickHandler    = function( event )
    {
        var clickOffset        = {
                x:    event.offsetX,
                y:    event.offsetY
            }, clickedBox    = {
                x:    Math.ceil( clickOffset.x / 50 ),
                y:    Math.ceil( clickOffset.y / 50 )
            };

        for( key in GridBox.boxesOnGrid ) {
            if( GridBox.boxesOnGrid[ key ].x === clickedBox.x && GridBox.boxesOnGrid[ key ].y === clickedBox.y ) {
                GridBox.clearGrid();
                GridBox.removeBox( key );
                GridBox.createGrid();
            }
        }

    };

    /**
     * Remove a box from the grid by removing it from the boxes array
     * and re-drawing the grid.
     */
    this.removeBox        = function( key )
    {
        alert( 'removing box ' + key );
        this.boxesOnGrid.splice( key, 1 );
    };

    /**
     * Create a box at a given coordinate on the grid
     * @param    {int} x
     * @param    {int} y 
     */
    this.createBoxAt    = function( x, y )
    {
        var box    = {
                x:    x * this.boxWidth - this.boxWidth,
                y:    y * this.boxHeight - this.boxHeight
            };

        this.createBox( box.x, box.y );
        this.saveBox( x, y );
    };

    this.createBox    = function( xpos, ypos )
    {
        this.context.rect( xpos, ypos, this.boxWidth, this.boxHeight );
        this.context.fillStyle    = '#444';
        this.context.fill();
    };

    this.saveBox    = function( x, y )
    {
        this.boxesOnGrid.push( { x: x, y: y } );
    };
}​
4

1 回答 1

4

工作小提琴

更改createBox为以下内容。

  this.createBox    = function( xpos, ypos )
    {
        this.context.beginPath();
        this.context.rect( xpos, ypos, this.boxWidth, this.boxHeight );
        this.context.fillStyle    = '#444';
        this.context.fill();
        this.context.closePath();
    };

您没有正确开始/结束路径，因此在重绘时不会清除先前的路径，从而再次将它们全部填充。另一种解决方法是直接使用fillRect。

创建路径的第一步是调用 beginPath 方法。在内部，路径存储为子路径（线、弧等）的列表，它们一起形成一个形状。每次调用此方法时，列表都会重置，我们可以开始绘制新形状。

延伸阅读

于 2012-06-27T23:12:16.223 回答