code: function(originalCall) {
      var call = originalCall.slice(),  // make a copy
          type = call[0];
      if (type in CALLS_XY) {
        var xys = CALLS_XY[type];
        if (typeof(xys) == 'number') xys = [xys];
        xys.forEach(function(pos) {
          call[1 + pos] = xScale(call[1 + pos]);
          call[2 + pos] = yScale(call[2 + pos]);
        });
      }
      if (type in CALLS_WH) {
        var whs = CALLS_WH[type];
        if (typeof(whs) == 'number') whs = [whs];
        whs.forEach(function(pos) {
          call[1 + pos] *= xScaling;
          call[2 + pos] *= yScaling;
        });
      }
      return call;
    }
docs: These calls are more complex: arc arcTo ellipse TODO: clip calls outside of the source rectangle.