lec 08 after class

8/12/2019 Lec 08 After Class

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2/24

1. If this is the header to a function defined inPicture.java:

public Picture scaleUp(int numTimes){....

}

What should the method call look like if I call it on aPicture object named pictObjand I wanted to usethe Picture object that it returns?

READING QUIZ

NO TALKING

CORRECTNESS MATTERS

A. Picture pictReturned = scaleUp(2);B. Picture pictReturned = pictObj.scaleUp(2);

C. String pictReturned = pictObj.scaleUp(2);

D. Picture = pictObj.scaleUp(2);


3/24

2.To scale a picture smaller by 2 (to make a copy of the picture that is half thesize of the source) what should go in the blanks

public void copySmaller(){

Picture pictObj = new Picture(FileChooser.pickAFile());

Pixel sourcePixel = null;Pixel targetPixel = null;

//loop through the columnsfor(int sourceX=0, targetX=0;

sourceX < pictObj.getWidth();____1_____, targetX++)

{//loop through the rows

for(int sourceY=0; targetY=0;soruceY < pictObj.getHeight();____2____, targetY++)

{sourcePixel = pictObj.getPixel(sourceX, sourceY);targetPixel = this.getPixel(targetX,targetY);

targetPixel.setColor(sourcePixel.getColor());}}

}A. 1. sourceX++ 2. sourceY+=2

B. 1. sourceX+=2 2. sourceY+=2

C. 1. sourceX+=2 2. sourceY++

D. 1. sourceX++ 2. sourceY++READING QUIZNO TALKINGCORRECTNESS MATTERS


4/24

3. How do I blend two picture objectswith 50% of one picture and 50% ofanother picture?

A. By multiplying their colors together and by 0.5

B. By adding them togetherC. By multiplying their colors by 0.5 and then adding

them

READING QUIZ

NO TALKING

CORRECTNESS MATTERS


5/24

4. Imagine that you have a method copyPictureTo, whose header is below, defined inPicture.java. This method copies the source Picture (sourcePic) and places its top leftcorner at (xStart, yStart) of the Picture that called the copyPictureTomethod.

public void copyPictureTo(Picture sourcePic, int xStart, int yStart)

Assume you have already created two Picture objects: sourcePic and pictObj, andyou make the following call:

pictObj.copyPictureTo(sourcePict, pictObj.getWidth()/2, 0);

Which position below best represents where the sourcePicwill be located in picObjafter the call? Assume that sourcePicis much smaller than pictObj.

READING QUIZNO TALKINGCORRECTNESS MATTERS

picObj

A B

C D

Arrows indicate

half the target

picture width and height


6/24

Mirroring Even Width versus Odd Width

int mirrorPt = getWidth() / 2;

...

for (int x = 0; x < mirrorPt; x++)


7/24

Mirroring Odd-width Pictures

What happens when this code attempts to mirror a Picture around the vertical

axis when the Pictures width is odd (e.g. 101)?

1) Solo: (30 sec)

2) Discuss: (2min)

3) Group: (30 sec)

int mirrorPt = getWidth()/2;

Pixel leftP, rightP;

for (int y = 0; y < getHeight(); y++)

{for (int x = 0; x < mirrorPt; x++)

{

leftP = getPixel(x,y);

rightP = getPixel(getWidth()-1-x,y);

rightP.setColor(leftP.getColor());

}}

A. It will work fine

B. It will run, but it wont

mirror correctly

C. I wont run, there will

be an index out ofbounds exception

D. It wont even compile

if getWidth() is odd


8/24

Mirroring Odd-width Pictures

What happens when this code attempts to mirror a Picture around the vertical

axis when the Pictures width is odd (e.g. 101)?

1) Solo: (30 sec)

2) Discuss: (2min)

3) Group: (30 sec)

int mirrorPt = getWidth()/2;

Pixel leftP, rightP;

for (int y = 0; y < getHeight(); y++)

{for (int x = 0; x < mirrorPt; x++)

{

leftP = getPixel(x,y);

rightP = getPixel(getWidth()-1-x,y);

rightP.setColor(leftP.getColor());

}}

A. It will work fine

B. It will run, but it wont

mirror correctly

C. I wont run, there will

be an index out ofbounds exception

D. It wont even compile

if getWidth() is odd


9/24

What are the first (x,y) coords fortopP and bottomP

to mirror around horizontalaxis?

topP bottomP

A. (0,0) (0,3)

(0,1) (0,2)

(1,0) (1,3)

B. (0,0) (0,3)

(1,0) (1,3)

(2,0) (2,3)

1) Solo: (30 sec)

2) Discuss (1 min)

3) Group

C. either A or B will work

D. none of the above


10/24

Challenge: Complete the code that mirrors inthe order specified by answer B

topP bottomPB. (0,0) (0,3)

(1,0) (1,3)

(2,0) (2,3)

int height = getHeight();

int width = getWidth();int mid = height/2;

Pixel topP, botP;

for ( ){

for( ) {topP = getPixel( );

botP = getPixel( );

botP.setColor(topP.getColor());

}

}


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12/24

Mirroring around horizontal axis

topP botPA. (0,0) (0,3)

(0,1) (0,2)

(1,0) (1,3)

int height = getHeight();

int width = getWidth();

int mid = height/2;

Pixel topP, botP;

for(int y=0; y


13/24

Challenge: What doesthis code do?

Hint: trace some of the getPixel index values.

int magic = getWidth()/2;

Pixel foo, bar;

for(int y = 0; y < getHeight(); y++)

{

int countingDown = getWidth()-1;

for(int x = 0; x < magic; x++)

{

foo = getPixel(x,y);

bar = getPixel(countingDown,y);

bar.setColor(foo.getColor());

countingDown--;}

}

A. Copies top half intobottom half notmirrored.

B. Copies left half intoright half notmirrored.

C. Mirrors aroundvertical axis, left intoright

D. Mirrors aroundhorizontal axis, topinto bottom

E. Some other bizarre

transformation

1) Solo: (1 min)

2) Discuss: (2 min)

3) Group: (30 sec)


14/24

Challenge: What doesthis code do?

Hint: trace some of the getPixel index values.

int magic = getWidth()/2;

Pixel foo, bar;

for(int y = 0; y < getHeight(); y++)

{

int countingDown = getWidth()-1;

for(int x = 0; x < magic; x++)

{


bar = getPixel(countingDown,y);

bar.setColor(foo.getColor());

countingDown--;}

}

1) Solo: (1 min)

2) Discuss: (2 min)

3) Group: (30 sec)

x

y

countingDown

foo bar


15/24

By what variable name do we refer tocollage inside makeC in Picture.java?

A. collage

B. callingObjec

C. Object

D. Picture

E. this

public class Lab4

{public static void main(String[] args)

{

Picture collage = new Picture("blank.jpg");

Picture p = new Picture("bird1.jpg");

Picture q = new Picture("bird2.jpg");

collage.makeC(p,q);}

}

public class Picture

{

public void makeC(Picture p1, Picture p2){

Pixel[] targetPixels = _______.getPixels();

// more code

}

}


16/24

Match the scenarioto the constructor call

(well vote for each scenario)

Scenario

1) Create a picture from a

specific file

2) Create a picture that is a

copy of another picture

3) Create a picture of a given

width and height4) Create a picture of the

same width and height as

another picture

Call

A. Picture p =

new Picture();

B. Picture p =

new Picture("filename.jpg");

C. Picture p =

new Picture(other);

D. Picture p =

new Picture(aNum,bNum);

1) S l (1 i )


17/24

What doesthis code do?

Makes red box of

width height

1) Solo: (1 min)

2) Discuss: (2 min)

3) Group: (30 sec)

Pixel foo;for(int y = 40; y < 50; y++)

{

for(int x = 1 ; x < 5; x++)

{


foo.setColor(Color.RED);}

}

1) S l (1 i )


18/24

What doesthis code do?

Makes red box of

width height

1) Solo: (1 min)

2) Discuss: (2 min)

3) Group: (30 sec)

Pixel foo;for(int y = 40; y < 50; y++)

{

for(int x = 1 ; x


19/24

What are correct loopsto make a black box of

width x and height y?public void foo(int x, int y) {

Pixel foo;

{

{

foo = getPixel(w,h);

foo.setColor(Color.BLACK);

}

}

}

1) Solo: (1 min)

2) Discuss: (2 min)

3) Group: (30 sec)

A) for (int w = 0; w


20/24

From the book: Cropping A Picture(page 147-148)well change a bit

Example of:

Working with both the calling object and a parameter

object in a method

Extra information is passed to methods through

parameters. The calling object is something like an extraparameter, named this

Doing something to a subset of the possible pixels in a

picture

1) Solo: (1 min)


21/24

What part of Katie are we copying?(slightmod from the book)

public void copyKatiesXXX(Picture sourcePic)

{

Pixel sPixel = null, tPixel = null;for (int sX = 40, tX = 100; sX < 110; sX++, tX++)

{

for (int sY = 350, tY = 100; sY < 400; sy++, tY++)

{

sPixel = sourcePic.getPixel(sX,sY);

tPixel = this.getPixel(tX,tY);tPixel.setColor(sPixel.getColor();

}

}

}

1) Solo: (1 min)

2) Discuss: (2 min)

3) Group: (30 sec)

A. Feet

B. Part of dress

C. Hands

D. Part of Couch

E. Face


22/24

Parameters: getting information in tomethods

Its nice to have code that is user controllable

We have been hard-coding constants (40, 3, 100,

for example) a lot, but we can write more flexible

code using PARAMETERS This lets us write code to do things like cropping

and pasting into a blank canvas, but letting the

user specify what part of the source picture to crop,and where to place it in the canvas.


23/24

Underline the values you would change intoparameters and write a new method header

public void copyKatiesXXX(

){

Pixel sPixel, tPixel = null;

for (int sX = 40, tX = 100; sX < 110; sX++, tX++)

{

for (int sY = 350, tY = 100; sY < 400; sy++, tY++)

{sPixel = sourcePic.getPixel(sX,sY);

tPixel = this.getPixel(tX,tY);

tPixel.setColor(sPixel.getColor();

}

}

}


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TODO

Study for In-term Exam 2

Start PSA4: Collage and Picture Flip

Dont forget your PSA3 interview!

lec 08 after class

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