什么是图形上下文？ (iOS)

Question

What exactly is a graphic context? When drawing with Core Graphic we get a reference to the context. When I look at the documentation it seems like it is an object or so that take care of the correct drawing whether it is for printing, device, pdf and so on.

Could anyone help me to understand what a context really is? I tried reading the documentation but I do not understand. Is it an object that contains information(meta-data) about a system or something?

Thanks in advance

Answer 1

"it seems like it is an object or so that take care of the correct drawing whether it is for printing, device, pdf and so on."

Exactly correct.

You simply write routines that "really" do some drawing (but it could be to anywhere, to any type of thing or device). You don't have to worry about ANYTHING other than drawing in the abstract ... lines, circles, typography, colours and other such nonsense.

-(void)happyDrawing
-(void)sadDrawing
-(void)fancyDrawing

Then -- amazingly -- you can use those anywhere.

-(void)makeSomeFiles
   {
   .. set up a context for making files
   .. happyDrawing
   }
-(void)makeATruGrayScaleBitmap
   {
   .. set up a context for making a gray bitmap
   .. happyDrawing
   }
-(void)drawRect
   {
   .. drawing on your Lisa screen
   .. happyDrawing
   }
-(void)drawRect
   {
   .. drawing on your iPad screen
   .. happyDrawing
   }
-(void)printAPage
   {
   .. set up a context for printing
   .. happyDrawing
   }

I hope it helps!

Answer 2

简而言之，图形在实际呈现之前被渲染或绘制的区域。

Answer 3

The graphics context determines how you are drawing to the screen, be it OpenGL or some 2D library. You should know this.