如何水平翻转图像

Question

我如何才能仅绘制两个带有反转的图像我不知道如何反转。 请帮忙。

    var canvas = document.createElement('canvas');
    canvas.width = 16 * scale;
    canvas.height = 32 * scale;
    //we assign the same classname the image has, for CSS purposes
    canvas.setAttribute('class', skinImage.getAttribute('class'));
    canvas.setAttribute('title', skinImage.getAttribute('title'));
    var context = canvas.getContext("2d"),
    s = scale;
    context.imageSmoothingEnabled=!1,
    context.mozImageSmoothingEnabled=!1,
    context.oImageSmoothingEnabled=!1,
    CanvasRenderingContext2D.webkitImageSmoothingEnabled=!1,
    context.clearRect(0,0,canvas.width,canvas.height);

    //back draw the head
    context.drawImage(skinImage, 24,  8,  8, 8,  4*s,  0*s,  8*s, 8*s);
    //back draw the body
    context.drawImage(skinImage, 32, 20, 8, 12, 4*s,  8*s,  8*s, 12*s);
    //back draw the right leg
    context.drawImage(skinImage, 52, 20, 4, 12, 12*s, 8*s,  4*s, 12*s);
    //back draw the right arm
    context.drawImage(skinImage, 12, 20, 4, 12, 8*s,  20*s, 4*s, 12*s);

    //back draw the left arm
    context.drawImage(skinImage, 12, 20, 4, 12, 4*s,  20*s, 4*s, 12*s);
    context.drawImage(skinImage, 52, 20, 4, 12, 0*s,  8*s,  4*s, 12*s);

Answer 1

首先，要删除2张不需要的图像，只需清除画布并重新绘制所需的图像即可。 您可以使用context.clearRect(0,0,canvas.width,canvas.height)清除画布。

水平翻转图像

如何水平翻转图像：

1. 将画布原点移动（平移）到所需的X坐标加上图像宽度： context.translate(x+img.width,y); 添加img.width是必要的，因为我们要抓住图像的左边缘并将其向左翻转。 如果不添加img.width，则会在所需的x坐标的左侧绘制img。

2. 使用context.scale(-1,1);水平翻转

3. 绘制图像：`context.drawImage（img，0,0）;

4. 通过将转换重置为其默认值进行清理： context.setTransform(1,0,0,1,0,0);

带注释的代码和演示：

 var canvas=document.getElementById("canvas"); var ctx=canvas.getContext("2d"); var cw=canvas.width; var ch=canvas.height; var img=new Image(); img.onload=start; img.src="https://dl.dropboxusercontent.com/u/139992952/multple/sillouette2.png"; function start(){ ctx.fillText('original',10,30); ctx.drawImage(img,10,30); ctx.fillText('flipped',150,30); flipHorizontally(img,150,30); } function flipHorizontally(img,x,y){ // move to x + img's width ctx.translate(x+img.width,y); // scaleX by -1; this "trick" flips horizontally ctx.scale(-1,1); // draw the img // no need for x,y since we've already translated ctx.drawImage(img,0,0); // always clean up -- reset transformations to default ctx.setTransform(1,0,0,1,0,0); } 

 #canvas{border:1px solid red; margin:0 auto; } 

 <canvas id="canvas" width=300 height=300></canvas> 

[添加：从Spritesheet翻转Sprite]

要翻转精灵表格中包含的精灵，可以使用drawImage的裁剪形式。 通过指定sprite的spriteX, spriteY, spriteWidth & spriteHeight裁剪drawImage将从spritesheet中裁剪所需的sprite。 通过指定所需的canvasX, canvasY, spriteWidth & spriteHeight同一裁剪drawImage还将裁剪的子图像绘制到画布上。

这是显示如何从Spritesheet翻转Sprite的代码

 var canvas=document.getElementById("canvas"); var ctx=canvas.getContext("2d"); var cw=canvas.width; var ch=canvas.height; var img=new Image(); img.onload=start; img.src="https://dl.dropboxusercontent.com/u/139992952/multple/cars.jpg"; function start(){ var spriteX=92; var spriteY=63; var spriteW=80; var spriteH=40; ctx.fillText('original',10,30); ctx.drawImage(img,spriteX,spriteY,spriteW,spriteH,10,30,spriteW,spriteH); ctx.fillText('flipped',150,30); flipSpriteHorizontally(img,150,30, spriteX,spriteY,spriteW,spriteH); } function flipSpriteHorizontally(img,x,y,spriteX,spriteY,spriteW,spriteH){ // move to x + img's width // adding img.width is necessary because we're flipping from // the right side of the img so after flipping it's still // at [x,y] ctx.translate(x+spriteW,y); // scaleX by -1; this "trick" flips horizontally ctx.scale(-1,1); // draw the img // no need for x,y since we've already translated ctx.drawImage(img, spriteX,spriteY,spriteW,spriteH,0,0,spriteW,spriteH ); // always clean up -- reset transformations to default ctx.setTransform(1,0,0,1,0,0); } 

 #canvas{border:1px solid red; margin:0 auto; } 

 <h4>Drawing & horizontally flipping a sprite</h4> <canvas id="canvas" width=300 height=100></canvas> <h4>Spritesheet:</h4> <img src='https://dl.dropboxusercontent.com/u/139992952/multple/cars.jpg'> 

Answer 2

镜像图像

这是一个简单的实用程序功能，它将在水平，垂直或两者上镜像。

// arguments
// ctx : the context on which to draw the mirrored image
// image : the image to mirror
// x,y : the top left of the rendered image
// horizontal : boolean if true mirror along X
// vertical : boolean if true mirror along y
function mirrorImage(ctx, image, x = 0, y = 0, horizontal = false, vertical = false){
    ctx.save();  // save the current canvas state
    ctx.setTransform(
        horizontal ? -1 : 1, 0, // set the direction of x axis
        0, vertical ? -1 : 1,   // set the direction of y axis
        x + horizontal ? image.width : 0, // set the x origin
        y + vertical ? image.height : 0   // set the y origin
    );
    ctx.drawImage(image,0,0);
    ctx.restore(); // restore the state as it was when this function was called
}

用法

mirrorImage(ctx, image, 0, 0, true, false); // horizontal mirror
mirrorImage(ctx, image, 0, 0, false, true); // vertical mirror
mirrorImage(ctx, image, 0, 0, true, true);  // horizontal and vertical mirror

更多镜子

如果您希望能够沿任意线镜像，请参见答案沿线镜像

Answer 3

要镜像图像，可以使用负缩放比例的setTransform 。

context.setTransform(-1, 0, 0, 1, 0, 0);    //Now all images will be horizontally mirrored
context.drawImage(<myimage>, srcx, srcy, srcw, srch, dstx, dsty, dstw, dsth);

完成后不要忘记恢复转换。

context.setTransform(1, 0, 0, 1, 0, 0);

Answer 4

function mirrorImage(image, src_x, src_y, img_width, img_height, x, y){

   // 1. MIRROR THE CANVAS
   context.scale(-1, 1);

   // 2. DRAW IN CANVAS USING (-X)
   context.drawImage(image, src_x, src_y, img_width, img_height, - x, y, 
   img_width, img_height);

   // 3. RETURN CANVAS TO ORIGINAL STATE (AFTER DRAWING)
   context.scale(-1, 1);

}