Ios graphics and plotting

1. ios provides two high-quality graphics rendering Methods: a. OpenGL ES for rendering B. Quartz, Core Animation, and UIKit for rendering

2. the OpenGL ES framework is mainly applicable to game or high frame rate application development. The C language-based interface is used to create 2D and 3D content.

UIKit Graphics System

3. All the pictures in iOS, No matter OpenGL ES, Quartz, UIKit, or Core Animation, occur in the area of the UIView object.

4. You can call drawRect to call UIView to trigger view update in the following situations:

A. Remove or delete other views of the blocked View

B. Set the hidden attribute to NO so that it changes from hidden to display.

C. will try to get out of the screen and return to the screen again

D. Call setNeedsDisplay or setNeedsDisplayInRect.

5. Ways to Improve the Performance of plotting:

A. Minimize the repainted Area

B. Try to make the view area opaque and set opaque to YES.

C. delete the alpha channel in the opaque PNG file. Deleting the alpha channel of the opaque PNG file can avoid the fusion operation on the layers that contain the image, thus greatly simplifying the image synthesis, this improves the plotting performance.

D. reuse existing views during Rolling

E. Avoid clearing the original content during the rolling process. By default, UIKit clears the context buffer of a region before calling the drawRect method to update a region of the view. If the buffer is cleared during the scrolling process, it is very costly. You can set the clearsContextBeforeDrawing attribute to NO.