Question

这句话的语法

So visitors have all the time they need to
enjoy their coffee outside while watching the people walk by
从while开始后面的语法解释

Answer 1

这句话相当于while (they are) watching the people walk by，是while引导的败哪时间状语从句。
while是连词, "while+doing"的结构是主句主语和从句主语一致的情况下，省略了主语和be动词。
they （主语）are watching（谓语）the people (宾语）walk by（宾补）.

张道真英语语法，第239页：
在某一动作进行时，另察山码一动作发生（这时分词短语前多加while或when）:
Be
careful when crossing the road.过马路要当心。（=When you cross...）
He got engaged to
her when travelling in Europe.在欧洲旅行时他和她订了婚。
She tremble a little while doing
so.她这样做时稍稍颤抖了一唯笑下。
While trying to open the door,I cut my
hand.在设法开门时我把手刺破了。
enjoy their coffee outside while watching the people walk by

Answer 2

while 在这句里是关连词，意思是同时（发生的），连接enjoy their coffee outside（在外羡让如头享受咖啡）和 watching the people walk by （看着路过的人滑伍）, 和中文的 ‘一边...一边' 相似’。句子可译为：因此兄启，游客们有充足的时间在外面一边享受咖啡一边观看行人走过。