HTML/Java Script Canvas - 如何在源点和目标点之间绘制图像? [英] HTML / Java Script Canvas - how to draw an image between source and destination points?

问题描述

我尝试使用画布的 drawImage 功能.

在文档中 (

I've tried to use the drawImage function of the canvas.

In the documentation (http://msdn.microsoft.com/en-us/library/ie/ff975414(v=vs.85).aspx) I thought the last two parameters are the destination point, but I guess it's not because it's not working.

Is there a way to draw image between two points without rotate it or something like this?

Thanks!

解决方案

context.drawImage( 
    sourceImage, 
    sourceX, sourceY, sourceWidthToClip, sourceHeightToClip, 
    canvasX, canvasY, scaledWidth, scaledHeight );

In context.drawImage the first parameter is the source image.

The next 4 parameters are the x,y,width & height rectangular sub-image to clip from that source

The last 4 parameters are the x,y,scaledWidth & scaledHeight rectangular scaled image to draw on the canvas.

Annotated drawImage:

context.drawImage(

    sourceImage,  // the source image to clip from

    sX,           // the left X position to start clipping 
    sY,           // the top Y position to start clipping
    sW,           // clip this width of pixels from the source
    wH,           // clip this height of pixels from the source

    dX,           // the left X canvas position to start drawing the clipped sub-image
    dY,           // the top Y canvas position to start drawing the clipped sub-image
    dW,           // scale sW to dW and draw a dW wide sub-image on the canvas
    dH            // scale sH to dH and draw a dH high sub-image on the canvas

}

Visual drawImage:

![enter image description here][1]

Code example for drawImage:

var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var canvas1=document.getElementById("drawImage");
var ctx1=canvas1.getContext("2d");

var img=new Image();
img.onload=start;
img.src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/avatars.jpg";
function start(){

  canvas.width=img.width;
  canvas.height=img.height;
  ctx.drawImage(img,0,0);

  var scale=2;
  canvas1.width=471/5*3;
  canvas1.height=255/2*3;

  ctx1.drawImage(img,
                 94,0,94,120,
                 50,50,94*scale,120*scale
                );
}

body{ background-color: ivory; padding:10px; }
canvas{border:1px solid red;}

<h4>The original image</h4>
<canvas id="canvas" width=300 height=300></canvas><br>
<h4>The clipped & scaled sub-image drawn into the canvas</h4>
<canvas id="drawImage" width=300 height=300></canvas>

Example Illustration for drawImage:

[ Addition: How to control dx,dy with html range controls ]

var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var canvas1=document.getElementById("drawImage");
var ctx1=canvas1.getContext("2d");

var $dx=$('#dx');
var $dy=$('#dy');
var scale=2;

var img=new Image();
img.onload=start;
img.src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/avatars.jpg";
function start(){

  canvas.width=img.width;
  canvas.height=img.height;
  ctx.drawImage(img,0,0);

  canvas1.width=471/5*3;
  canvas1.height=255/2*3;

  draw();

  $dx.change(function(){draw();});
  $dy.change(function(){draw();});

}

function draw(){
  ctx1.clearRect(0,0,canvas1.width,canvas1.height);
  ctx1.drawImage(img,94,0,94,120,$dx.val(),$dy.val(),94*scale,120*scale);
}

body{ background-color: ivory; padding:10px; }
canvas{border:1px solid red;}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<h4>The original image</h4>
<canvas id="canvas" width=300 height=300></canvas><br>
<h4>The clipped & scaled sub-image drawn into the canvas</h4>
dx:<input id=dx type=range min=0 max=280 value=0><br>
dy:<input id=dy type=range min=0 max=380 value=0><br>
<canvas id="drawImage" width=300 height=300></canvas>

[1]: http://i.stack.imgur.com/9paHM.jpg

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