June 2013
Intermediate to advanced
360 pages
6h 50m
Chinese
Content preview from COCOA學習手冊--使用OBJECTIVE-C第三版
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在視圖中繪圖
|
105
圖 7-3 描邊且內部被填滿的軌跡
圖素網格
iOS 與 OS X 裡的所有展示系統皆奠基於
圖素網格
（
grid of pixels
）的觀念。顯示器上的
具體圖素數量隨裝置不同而異，每個圖素的實際尺寸也一樣。基本的趨勢為較小的圖素
搭配較多的數量，因為圖素越小，圖像看起來越平滑。
建立圖形上下文時，你指明作業環境應該是什麼尺寸，因此，舉例來說，如果你建立高
400 圖素、寬 300 圖素的圖形上下文，畫布便會被調整到那樣的尺寸。在畫布以外發生
的任何繪圖工作都會被忽略，而且不會出現在畫布上 ( 圖 7-4)。
建立圖形上下文定義繪圖作業發生的
座標空間
，該座標空間以左上角為 (0,0)（在 iOS
上）或者左下角為 (0,0)（在 OS X 上）。當你建立軌跡時，你指明定義它的點（point）。
因此，舉例來說，在 iOS 上，一條從左上角往右下方延伸 10 個圖素的直線看起來就像
圖 7-5 那樣。
視網膜顯示
Apple 最新販售的裝置標榜著
視網膜顯示
（
Retina display
）的強大功能，根據 Apple
的說法，視網膜顯示意味著螢幕上的圖素非常小，以致於你根本無法分清楚個別的點
（dot）。這表示，曲線和文字看起來會平滑很多，最終結果是提供使用者更精采的視覺
體驗。
在本書出版時，MacBook Pro with Retina Display、iPod Touch 第 4 代（含）以上、
iPhone 4（含）以上、和 iPad 第 3 代（含）以上的硬體版本均支援視網膜顯示。 ...
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and much more.
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.