Core Graphics

Question 1

What is a graphics context (CGContextRef)?

Answer 1

An opaque data type that Quartz uses to draw images to screen, bitmap, PDF file, etc.

Question 2

How ubiquitous is CGContextRef?

Answer 2

All objects in Quartz are drawn to, or contained by, a graphics context.

Question 3

Think of a graphics context (CGContextRef) as a …..?

Answer 3

Drawing destination.

Question 4

What is CGLayerRef?

Answer 4

An offscreen drawing destination associated with another graphics context.

Question 5

What prefix is used for functions in the Core Graphics API?

Answer 5

CG for Core Graphics.

Question 6

What is used for offscreen drawing?

Answer 6

CGLayerRef

Question 7

What is the graphics state?

Answer 7

The graphics state contains parameters that would otherwise be taken as arguments to drawing routines.

Question 8

Can graphics states be saved?

Answer 8

Yes. There is actually a stack of them.

Question 9

My code specifies locations and sizes in which coordinate system

Answer 9

User-space

Question 10

How is user space mapped to device space?

Answer 10

With a content transformation matrix, or CTM.

Question 11

The content transformation matrix is what kind of matrix?

Answer 11

An Affine transform.

Question 12

How is UIKit’s coordinate system different from Quartz’s?

Answer 12

In Quartz, the y-axis goes up, whereas in UIKit it grows down.

Question 13

How is memory management done in Core Graphics?

Answer 13

With reference counting.

Question 14

When do I own a reference to an object?

Answer 14

If I got it from a function with name beginning with Copy or Create.

Question 15

How do I draw to the screen in an iOS application

Answer 15

With [UIView drawRect:]

Question 16

In [UIView drawRect:] how do I get a graphics context?

Answer 16

By calling UIGraphicsGetCurrentContext()

Question 17

In [UIView drawRect:] how are coordinate systems handled?

Answer 17

The UView modified the coordinate transformation matrix so as to flip the y-axis.

Question 18

What is anti-aliasing?

Answer 18

Artificially correcting jagged edges in text glyphs and bitmaps.

Question 19

Can anti-aliasing be turned on and off?

Answer 19

Yes, with CGContextSetShouldAntialias().

Question 20

A path consists of one or more …

Answer 20

Subpaths

Question 21

A subpath consists of:

Answer 21

straight lines, curves, or both.

Question 22

Is a path open or closed?

Answer 22

It can be either.

Question 23

What is stroking a path?

Answer 23

Actually drawing its line.

Question 24

What is filling a path?

Answer 24

Filling the interior of a closed path.

Question 25

Can a path be stroked/not stroked and filled/not filled independently?

Answer 25

Yes

Question 26

Can be path be used to define a clipping area?

Answer 26

Yes

Question 27

Can a path consist of subpaths that don't intersect on another?

Answer 27

Yes

Question 28

What is done before stroking or filling a path?

Answer 28

The path must be created first.

Question 29

How do you specify the starting point for a new subpath?

Answer 29

CGContextMoveToPoint()

Question 30

Regarding point (in a coordinate system), Quartz always keeps track of the ...

Answer 30

current point.

Question 31

How can you add a series of connected lines to a path?

Answer 31

CGContextAddLines()

Question 32

How is an arc added to a path?

Answer 32

CGContextAddArc()

Question 33

What is used for curvilinear shapes

Answer 33

Quadratic and cubic Bezier functions.

Question 34

What is the advantage of using a formula for a curve?

Answer 34

1) It is compact to store, and 2) it can be reproduced at any resolution.

Question 35

A cubic Bezier curve uses two endpoints and ...

Answer 35

Two control points.

Question 36

A quadratic Bezier curve uses two endpoints and ...

Answer 36

One control point.

Question 37

How can I always close a subpath?

Answer 37

With CGContextClosePath(). This adds a line segment from the current point to the subpath's starting point.

Question 38

What shapes can easily be added to the current path (as their own subpaths)?

Answer 38

Ellipses and rectangles.

Question 39

How to create a path and set its starting point?

Answer 39

CGContextBeginPath() and GGContextMoveToPoint()

Question 40

What are some parameters that affect path stroking?

Answer 40

line width, line join, line cap

Question 41

How does path filling work with subpaths?

Answer 41

When you fill the current path, Quartz acts as if each subpath contained in the path were closed.

Question 42

What are blend modes?

Answer 42

Blend modes specify how Quartz applies paint over a background.

Question 43

What is the alpha value?

Answer 43

It determines how to composite newly painted objects to the existing page. 1=opaque, 0=invisible.

Question 44

Besides specifying alpha as part of a color, what else can I do?

Answer 44

I can set a global alpha value with CGContextSetAlpha().

Question 45

Do the current colors "stick" in the graphic state?

Answer 45

Yes

Question 46

Are user-space coordinates related to the pixel-resolution of the device space?

Answer 46

No

Question 47

Before transforming the CTM, you should...

Answer 47

Save the graphics state so that it can be restored.

Question 48

What is a pattern?

Answer 48

A sequence of drawing operations that is repeatedly painted to a graphics context.

Question 49

What is a shadow?

Answer 49

An image painted underneath, and offset from, a graphics object.