翻转图像和HTML5画布中绘制的线条

Question

我正在使用画布加载图像。在图像上画一些线条。然后我想点击一个“翻转”按钮来翻转图像和我刚绘制的线条。代码为here on jsfiddle。

我目前的问题是：

1. 我绘制的线条不会被翻转，但是在我之后图像被翻转 单击“翻转”按钮。
2. 我不会立即出现这些线条 单击“翻转”按钮。我开始画画时会显示这些线条 试。

任何帮助将不胜感激。

谢谢，

var context;
var canvas;
var imageObj = new Image();
var flipH = true;
var flipV = true;
var scaleH = 1,
    scaleV = 1;
var posX = 0,
    posY = 0;
var isDrawingFreeDraw;


    canvas = document.getElementById('myCanvas');
    context = canvas.getContext('2d');
    context.strokeStyle = "#FFFF00";
    //context.save();
    canvas.addEventListener('mousedown', MouseDown, true);
    canvas.addEventListener('mouseup', MouseUp, true);
    canvas.addEventListener('mousemove', MouseMove, true);
    imageObj.src = 'http://upload.wikimedia.org/wikipedia/commons/1/1a/Image_upload_test.jpg';


    imageObj.onload = function () {
        context.drawImage(imageObj, posX, posY, canvas.height * imageObj.width / imageObj.height, canvas.height);
    };


    console.log(context);


$(document).on('click', '#FlipH', function () {
    console.log("Flip Me");
    //    context.restore();
    context.save();
    //canvas.width = 100;
    scaleH = flipH ? -1 : 1;
    context.scale(scaleH, scaleV);
    posX = flipH ? (canvas.height * imageObj.width / imageObj.height) * -1 : 0;
    context.drawImage(imageObj, posX, posY, canvas.height * imageObj.width / imageObj.height, canvas.height);
    flipH = !flipH;
    context.scale(1, 1);
    //console.log(context);

    context.restore();

});



function MouseUp(e) {
    isDrawingFreeDraw = false;
    context.save();

}

function MouseDown(e) {
    context.save();

    isDrawingFreeDraw = true;
    console.log(e);
    context.moveTo(e.pageX, e.pageY);
    context.restore();

}

function MouseMove(e) {
    if (isDrawingFreeDraw) {
        context.save();

        context.lineTo(e.pageX, e.pageY);
        context.stroke();
        context.restore();

    }
}

Answer 1

要翻转图像和图形，可以使用画布本身作为drawImage的源。

// draw the canvas to itself

ctx.drawImage(canvas,0,0);

演示：http://jsfiddle.net/m1erickson/Y9SLQ/

示例代码：

var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");

var img=new Image();
img.onload=start;
img.src="http://upload.wikimedia.org/wikipedia/commons/1/1a/Image_upload_test.jpg";
function start(){

    canvas.width=img.width;
    canvas.height=img.height;

    ctx.drawImage(img,0,0);

    ctx.beginPath();
    ctx.moveTo(50,50);
    ctx.lineTo(50,300);
    ctx.lineTo(250,300);
    ctx.lineWidth=8;
    ctx.stroke();

}


$("#flipbutton").click(function(){
    ctx.save();
    ctx.translate(canvas.width,0);
    ctx.scale(-1,1);
    ctx.drawImage(canvas,0,0);
    ctx.restore();
});