EzWindows API

A Graphical Application Programmer Interface

JPC and JWD © 2002 McGraw-Hill, Inc. Modified by S. Sudarshan

Examples

EzWindows library provides several graphical types and classesExamples:

SimpleWindow is a class for creating and manipulating window objects

RectangleShape is a class for creating and manipulating rectangle objects

EzWindows Library Objects

Definitions are the same form as other objectsExample

SimpleWindow W;

Most non-fundamental classes have been created so that an object is automatically initialized to a sensible value

SimpleWindow objects have member functions to process messages to manipulate the objects

Most important member function is Open() which causes the object to be displayed on the screen Example

W.Open();

Initialization

Class objects may have several attributes to initialize

Syntax for initializing an object with multiple attributes

Type Identifier(Exp1, Exp2, ..., Expn);

SimpleWindow object has several optional attributes

SimpleWindow W("Window Fun", 8, 4);

First attribute Window banner

Second attribute Width of window in centimeters

Third attribute Height of window in centimeters

An EzWindows Program

#include <iostream>using namespace std;#include "ezwin.h"int ApiMain() {

SimpleWindow W("A Window", 12, 12);W.Open();

cout << "Enter a character to exit" << endl;char a;cin >> a;

return 0;}

Sample Display Behavior

RectangleShape ObjectsEzWindows (rect.h/rect.cc) provides RectangleShape for manipulating rectangles

RectangleShape objects can specify the following attributes

SimpleWindow object that contains the rectangle (mandatory)

Offset from left edge of the SimpleWindow

Offset from top edge of the SimpleWindow Offsets are measured in centimeters from rectangle center

Color color is an EzWindows enumerated type, with allowed values

Black, White, Red, Green, Blue, Yellow, Cyan, Magenta

Width, Height (in centimeters)

RectangleShape Objects

ExamplesSimpleWindow W1("My Window", 20, 20);

SimpleWindow W2("My Other Window", 15, 10);

RectangleShape R(W1, 4, 2, Blue, 3, 2);

RectangleShape S(W2, 5, 2, Red, 1, 1);

RectangleShape T(W1, 3, 1, Black, 4, 5);

RectangleShape U(W1, 4, 9);

RectangleShape Objects

Some RectangleShape member functions for processing messages

Draw() Causes rectangle to be displayed in its associated

window

GetWidth() Returns width of object in centimeters

GetHeight() Returns height of object in centimeters

SetSize() Takes two attributes -- a width and height -- that

are used to reset dimensions of the rectangle

Another EzWindows Program

#include <iostream>using namespace std;#include "rect.h"int ApiMain() {

SimpleWindow W("Rectangular Fun", 12, 12);W.Open();RectangleShape R(W, 5.0, 2.5, Blue, 1, 2);R.Draw();cout << "Enter a character to exit" << endl;char Response;cin >> Response;return 0;

}

Sample Display Behavior

EzWindows Coordinate System

Use centimeters Metric Simpler to understand

than pixels Device independent Helps introduce

notionof information hidingor encapsulation

Length of window (10 cm)

Height of window (5 cm)

X coordinate: distancefrom left edge of

screen (4 cm)

Y coordinate:distance from topof screen (4 cm)

Class Position

For earlier objects, the position was specified by given both an x-coordinate and a y-coordinateWe can now introduce a new object called Position and use it

Position

class Position {public:

Position(float x = 0.0, float y = 0.0);float GetXDistance() const;float GetYDistance() const;Position Add(const Position &p) const;

protected:void SetXDistance(float x);void SetYDistance(float y);

private:float XDistance;float YDistance;

};

Position operator+(const Position &x, const Position &y);

Other Shapes

EzWindows also provides several other shape constructors defined in files circle.h, triangle.h, square.h, label.h,

ellipse.h, ray.h etc (see EzWindows/include directory) RectangleShape(window, center-position, color=Red,

length, width) CircleShape (window, center-position, color=Black,

diameter=1) TriangleShape (window, center-position, color=Black,

sidelength=1) SquareShape (window, center-position, color=Red, side = 1) Label (window, position, text, color=Black) EllipseShape (ellipse.h) RaySegment (lines with arrow heads) (ray.h)

Each of these has a Draw() and an Erase() method

Using Direct Rendering

The SimpleWindow class also provides a number of methods that let you directly draw shapes, without creating shape objects

RenderText, RenderRectangle, RenderLine, RenderEllipse, RenderPolygon etc.

Class SimpleWindow

Writing text in a window

void SimpleWindow::RenderText(const Position

&UpperLeft, const Position &LowerRight,

const string &Msg = "Message",

const color &TextColor = Black,

const color &BackGroundColor = White)

First coordinate of thebounding box

Second coordinate ofthe bounding box

Message

Hello EzWindows#include <assert.h>#include "ezwin.h"

// Create a 10 x 4 windowSimpleWindow HelloWindow("Hello EzWindows", 10.0, 4.0, Position(5.0, 6.0));

// ApiMain(): create a window and display greetingint ApiMain() {

HelloWindow.Open();assert(HelloWindow.GetStatus() == WindowOpen);

// Get Center of WindowPosition Center = HelloWindow.GetCenter();

Hello EzWindows

// Create bounding box for textPosition UpperLeft = Center + Position(-1.0, -1.0);Position LowerRight = Center + Position(1.0, 1.0);

// Display the textHelloWindow.RenderText(UpperLeft, LowerRight, "Hello EzWindows", Black, White);

return 0;}

Hello EzWindows

// ApiEnd(): shutdown the windowint ApiEnd() {

HelloWindow.Close();

return 0;}

Class SimpleWindow

Simple Window constructor

SimpleWindow::SimpleWindow(

const string &t =

"Untitled",

float w = 8,

float h = 8,

const Position &p = Position(0,0)

)

Window Member Functions for Rendering Shapes

See include/SimpleWindow.h for prototypes also see files in samples directory, e.g. basic.cpp for examples

RenderRectangle(position1 (UL), position2 (LR), fillcolor, border)

UR: Upper Left LR: Lower Right

RenderLine (position1, position2, color, thickness)RenderEllipse(position1 (UL), position2 (LR), fillcolor, border)RenderPolygon(position[], numpoints, fillcolor, border)RenderText … seen already Message(string): alert box with specified message

Bitmaps

Class BitMap

Uses BitMapStatus

enum BitMapStatus {NoBitMap, BitMapOkay, NoWindow

};

Class BitMap

Class BitMap can display .bmp files in a SimpleWindow window

BitMap’s constructor isBitMap::BitMap(SimpleWindow &w)

Additional key member functions areBitMapStatus BitMap::Load(string Filename)BitMapStatus BitMap::GetStatus() constvoid BitMap::SetPosition(const Position &p)int BitMap::Draw()int BitMap::Erase()int BitMap::IsInside(const Position &p) const

Fun with Pictures// Display a bit map image of the authors in the // center of a window#include <assert.h>#include "bitmap.h"

// Open a window to display photographSimpleWindow PhotoWindow("The Authors", 10.0, 7.0, Position(5.0, 3.0));

// ApiMain(): display a bitmap photoint ApiMain() {

PhotoWindow.Open();assert(PhotoWindow.GetStatus() == WindowOpen);const Position WindowCenter = PhotoWindow.GetCenter();

Fun with Pictures

// Create a bitmapBitMap Photo(PhotoWindow);

// Load the imagePhoto.Load("photo.bmp");

// on Linux, .xpm; to generate xpm from other // formats, use “convert photo.jpg photo.xpm”assert(Photo.GetStatus() == BitMapOkay);

// Compute position of logo so it is centeredPosition PhotoPosition = WindowCenter + Position(-.5 * Photo.GetWidth(), -.5 * Photo.GetHeight());Photo.SetPosition(PhotoPosition);

// Draw bitmap and we’re donePhoto.Draw();

return 0;}

Fun with Pictures

Event-based Programming

Messages are sent to your program by the operating system

Mouse down Mouse up Key down Key up Refresh Quit Timer

Handle messages by registering a call back

C: User Program

C: SimpleWindow User start

Mouse click

Timer tick

User end

EzWindows Auxiliary Functions

long int GetMilliseconds() Returns the value of a timer that is ticking

continuously. The resolution of the timer is milliseconds.

void Terminate() Sends a terminate message to the EzWindows

window manager.

Mouse Events

Before we can react to a mouse event in a SimpleWindow Must tell window what function to call when an event

occurs Registering a callback

To register a callback use the SimpleWindow member function SetMouseClickCallback.

W1.SetMouseClickCallback(f);

Says if the mouse is clicked in window W1, call function f() f() is passed a Position that is the coordinate of

the location of the mouse when the button was clicked

Mouse Eventsint ApiMain() {

// Open the windowW1.Open(); assert(W1.GetStatus() == WindowOpen);

// Load the imageB.Load("wizards.bmp"); assert(B.GetStatus() == BitMapOkay);

// Display the bit maps at a starting positionB.SetPosition(Position(1.0, 1.0));B.Draw();

// Register the callbacks for each windowW1.SetMouseClickCallback(ReceiveMouseClick);

return 0;}

Mouse Events

#include <assert.h>#include "bitmap.h"SimpleWindow W1("Window One", 10.0, 7.0, Position(1.0,

1.0));

BitMap B(W1); // Define a bitmap

// Mouse callback functionint ReceiveMouseClick(const Position &p) {

// Erase the bitmapB.Erase();

// Set its new position and display itB.SetPosition(p);B.Draw();

return 1;}

Timer Events

The SimpleWindow class supports a timer mechanism

You can set a timer to go off periodically

When the timer goes off, a call back is made to the function specified by the user

Timer Functions

void SimpleWindow::SetTimerCallback( TimerTickCallbackFunction f)

Registers a callback for a timer tick Function f() will be called when a timer tick occurs. The function f() must be declared to take no

parameters, and it should return an int The return value of f() indicates whether the event

was handled successfully A value of 1 is to indicate success A value of 0 is to indicate an error occurred

Timer Functions

int SimpleWindow::StartTimer(int Interval) Starts timer running Parameter Interval is the number of milliseconds

between timer events The return value indicates whether the timer was

successfully started A return value of 1 indicates success A return value of 0 indicates the timer could not be

set up

void SimpleWindow::StopTimer() Turns timer off

#include <assert.h>#include "bitmap.h“

SimpleWindow W1("Fun", 15.0, 9.0, Position(1.0, 1.0));

BitMap B(W1); // Define a bitmap

// W1TimerEvent(): move bitmap to a new locationint W1TimerEvent() {

// Erase the bitmapB.Erase(); // Compute a new position and display it// Make sure the bitmap is completely in the windowint XCoord = Uniform(1, W1.GetWidth());if (XCoord + B.GetWidth() > W1.GetWidth())

XCoord = XCoord - B.GetWidth();int YCoord = Uniform(1, W1.GetHeight());if (YCoord + B.GetHeight() > W1.GetHeight())

YCoord = YCoord - B.GetHeight();B.SetPosition(Position(XCoord, YCoord));B.Draw();

}

Example

Example

int ApiMain() {W1.Open(); // Open the windowassert(W1.GetStatus() == WindowOpen);B.Load("davidson.bmp"); // Load the imageassert(B.GetStatus() == BitMapOkay);

// Display the bit maps at a starting positionB.SetPosition(Position(1.0, 1.0));B.Draw();

// Register the callbacks for each window// and start the timers to go off every 500 msW1.SetTimerCallback(W1TimerEvent);W1.StartTimer(500);return 0;

}

Example

int ApiEnd() {// Stop the timers and close the windowsW1.StopTimer();W1.Close();return 0;

}