Pan and Scale in the Same Operation

To pan and scale in the same operation, we simply need to pan using the same window and window properties as Example 4-14 and the same source scale factor as Example 4-15:

var windowX=1580;
var windowY=1190;

In the drawScreen() function, we will use this to draw the image:

context.drawImage(photo, windowX, windowY,windowWidth*2,windowHeight*2,

Example 4-15 shows this powerful combination in action.

Example 4-15. Scale and pan to a spot on the image

var photo=new Image();
photo.addEventListener('load', eventPhotoLoaded , false);

var windowWidth=500;
var windowHeight=500;
var viewPortWidth=500;
var viewPortHeight=500;

var windowX=1580;
var windowY=1190;

function eventPhotoLoaded() {

function drawScreen(){
        context.drawImage(photo, windowX,

When Example 4-15 is run, you will see that we have panned to a new spot on the large image and doubled the size of the image source rectangle. This acts as a zoom-out feature, and the butterfly becomes much clearer than in Example 4-14. Figure 4-16 shows this example in action.

Pan and scale applied to the butterfly image

Figure 4-16. Pan and scale applied to the butterfly image

Next we take a look at manipulating individual pixels on the canvas.

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