如何水平翻转图像

Question

我怎样才能只绘制两个反转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 个不需要的图像，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，img 将绘制在所需 x 坐标的左侧。

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来进行清理：

   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：从精灵表中翻转精灵]

要翻转精灵表中包含的精灵，您可以使用

drawImage

的裁剪形式。裁剪drawImage将通过指定精灵的

spriteX, spriteY, spriteWidth & spriteHeight

从精灵表中裁剪所需的精灵。同样的裁剪drawImage也会通过指定所需的画布将裁剪后的子图像绘制到画布上

canvasX, canvasY, spriteWidth & spriteHeight

。

这里的代码展示了如何从精灵表中翻转精灵

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函数，可以水平、垂直或两者镜像图像。

// 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
}

使用方法

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，请参阅答案 沿线镜像

Answer 3

要镜像图像，您可以使用带有负比例的

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变换。

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 CONTEXT
   context.scale(-1, 1);

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

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

}

Answer 5

使用变换矩阵：
https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/setTransform

ctx.setTransform(
  -1, 0,
   0, 1,
   canvasWidth,
   0
);

或者翻译然后缩放：
https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/transform https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/scale

ctx.transform(canvasWidth, 0);
ctx.scale(-1, 1);