画布中心等距地图？(Center isometric map in canvas?)

 我想知道如何设置画布来查看特定的网格点？ 
 
 例如，我的等轴测图使用x：y坐标。 当我加载地图是一些关于画布，大约一半的..所以我想将相机的中心设置为地图的中心区域。 这样整个网格就可以在画布中查看。 
 
img.onload = function(){
tiles_wide = 18; 
tiles_long = 19; 

for (i=0;i<tiles_wide;i++){ //horizontal

  for (j=0;j<tiles_long;j++){ // vertical

    var x = (i-j)*(img.height/2);
    var y = (i+j)*(img.height/4);

    ctx.drawImage(img,x,y);
        }
    }

}
 
 希望有人可以帮忙:) 

I was wondering how to set canvas to view a specific grid spot ?
 
For example, my isometric map uses x:y co ordinates. And when i load the map is some what off the canvas, about half of it.. so i want to set the center of the camera to the center tile of the map. So that the entire grid is viewable in the canvas.
 
img.onload = function(){
tiles_wide = 18; 
tiles_long = 19; 

for (i=0;i<tiles_wide;i++){ //horizontal

  for (j=0;j<tiles_long;j++){ // vertical

    var x = (i-j)*(img.height/2);
    var y = (i+j)*(img.height/4);

    ctx.drawImage(img,x,y);
        }
    }

}
 
Hope some one can help :)

原文：https://stackoverflow.com/questions/9439337