HTML 5 Canvas 似乎重绘了删除的部分 [英] HTML 5 Canvas seems to redraw removed parts

问题描述

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！我做错了什么?

I have created the following code on jsfiddle. The goal is to remove a box from the canvas after it has been clicked. What actually happens is that the grid is cleared and completely redrawn WITH the removed box in it's old spot. The grid will only appear empty when all of the given objects have been removed... I am puzzled! What am I doing wrong?

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 } );
    };
}​

推荐答案

工作小提琴

将 createBox 更改为以下内容.

Change createBox to the following.

  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.另一种解决方法是改用 fillRect.

Your not properly starting/ending paths, so the previous path isnt cleared when you redraw thus filling them all in again. Another way around it is to just use fillRect instead.

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.

The first step to create a path is calling the beginPath method. Internally, paths are stored as a list of sub-paths (lines, arcs, etc) which together form a shape. Every time this method is called, the list is reset and we can start drawing new shapes.

进一步阅读

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