TweetFollow Us on Twitter

Foundation Of Quickdraw
Volume Number:1
Issue Number:2
Column Tag:features of Mac Pascal

QuickDraw Graphics

By Chris Derossi

One of the most valuable features of Mac Pascal is it ability to take advantage of the Macintosh’s powerful ROM capabilities. To do this, Mac Pascal must be able to access the various routines that are contained within the Mac Toolbox. In this month’s column, we will examine the interface between Mac Pascal and the ROM, and the necessary data structures for accessing quickdraw. Finally, a sample program is included which makes use of quickdraw’s graphics routines.

In order to communicate to the Toolbox, several data structures have to be defined. These data structures are all presented in Pascal format because the routines contained in the Mac ROM are constructed for a Pascal environment. Unlike other programming languages, this makes data compatiblitly pretty much straight forward for Mac Pascal users. But before we get into the details, let’s briefly describe some of the theory behind QuickDraw.

FOUNDATION OF QUICKDRAW

QuickDraw graphics exist in cartesian coordinate planes. What this means is that graphics may be present on any portion of a continuous surface. The QuickDraw planes are finite, and extend from values -32768 to 32767 in both the vertical and horizontal directions. The smallest unit of distance that QuickDraw can work with is 1. An area of 1 by 1 is, therefore, a point. The boundary separating two points at sequential locations of the plane is of size zero. This means that two points placed next to each other are continuous, and have no space between them. Keep in mind that these are theoretical concepts, not screen bit-map specifications.

QUICKDRAW DATA STRUCTURES

In Mac Pascal, the data structure ‘Point’ is a record with two components representing the coordinates of the upper left corner of a point. The two fields of Point are Point.h and Point.v which are the horizontal and vertical coordinates respectively. Each value is of type Integer.

The rectangle is a common object found in QuickDraw. Rectangles are frequently used to create windows, define drawing areas, and to provide parameters for manipualting other objects. A rectangle has four parameters. These are: Top, Left, Bottom, and Right. These parameters may be thought of as four integers, or as the two points TopLeft and BottomRight. In actuality, the second method is used, and the type ‘Rect’ is defined as a record with the two fields Rect.TopLeft and Rect.BotRight. Each of the fields is of type point.

Another object defined with points is the line. Although there is no Mac Pascal data type for this object, it can be characterized by two points, for the beginning and ending positions of the line.

The final data type we will examine this month is the pattern. QuickDraw allows regions to be filled with patterns, as is done with the paint bucket in MacPaint. A pattern is a set of sixty-four points either on or off, arranged in an eight by eight square. To fill an area larger than eight by eight, the Macintosh repeats the pattern both vertically and horizontally as many times as neccessary. The upper left corner of the pattern is aligned with the coordinate (0,0), and is independent of the coordinates of the area being filled.

Since a byte is eight bits, and a bit represents one point, patterns can be represented as a series of eight bytes. In Mac Pascal, the type ‘Pattern’ is an array [0..7] of 0..255, which is effectively eight sequential bytes. There are some predefined patterns including White, Black, and Grey.

DRAWING IN QUICKDRAW

The drawing mechanism in QuickDraw is the Pen. The pen has modifyable properties which include location, width, height, and pattern. There are further properties which will be covered in a later column. A pen of width and height of one, and a pattern of black will always draw with one-point wide, black lines.

In addition to the many objects of QuickDraw, many actions are available to be performed on or with them. Most objects may be Framed, Painted, Filled, and Erased. The QuickDraw actions are called QuickDraw verbs, and they are applied to objects. The verb Frame specifies that the outline of the given object should be drawn. The verb Paint means that the object is drawn completely filled. Each of these actions use the pen for drawing, and as such use the current pen pattern. The verb Erase does not use the pen pattern, but instead uses the pattern currently set for the background. Fill allows you to specify a pattern to use, and is therefore a little bit more versatile than Paint.

For example, FrameRect will draw the outline of a rectangle, while PaintRect will draw a solid rectangle. FillRect will draw a solid rectangle in the given pattern. EraseRect clears the given rectangle to the current background pattern.

Each verb-object combination is a procedure, and takes applicable parameters. The Rect procedures take a rectangle as their only parameter. The FillRect procedure needs a Rect first, and a Pattern second. The rectangle is drawn as a solid with the pattern.

A frequently encountered situation is one where the Macintosh needs to know if a given point is inside a particular rectangle. (i.e. is the mouse’s position inside a certain window?) To satisfy this need, a function titled PtInRect returns a boolean of True if the point is inside the rectangle, and False if not. The parameters of this function are a point first, and then a rectangle.

PROGRAMMING EXAMPLE

Now let us examine the example program that makes use of these data structures, procedures, and functions. The operation of the program is fairly simple and straight forward. The user is presented with a blank background and the mouse pointer. The user forms rectangles by pressing the mouse button when the pointer is at one of the rectangle’s corners, and holds the button down while dragging the mouse to the opposite diagonal corner. In order to provide some feedback about the shape of the rectangle, a ‘rubber banding’ diagonal line follows the mouse until the button is released. When the button is released, the rubber band line is removed, and the rectangle is drawn.

WHERE’S THE MOUSE?

After the rectangle is drawn, the user may place the mouse pointer inside the rectangle, and press the button. As long as the button is held, the Mac continually fills the rectangle with random, changing patterns. Once the mouse button is pressed outside of the rectangle, the pattern is frozen, and a new rectangle is begun. (Please see the sample output in fig. 1.)

The construction of the program is not complex. The variable declarations for the main program consist of three points and one rectangle. The points are used as work variables for reading the mouse location, and the rectangle is the one currently being drawn or filled.

The main program calls two procedures. The first one allows the user to create the rectangle, and provides the rubberbanding effect. The second one creates random patterns and fills the rectangle.

Since the value of a rectangle’s Top must be less than or equal to that of its bottom, two procedures called ‘Min’ and ‘Max’ help keep the points in the right order. The same holds true for the Left and Right values.

The key procedure calls in the Make_Rect procedure are Button, GetMouse, DrawLine, PenPat, FrameRect, and InsetRect. The function Button returns True if the mouse button is pressed, and False if not. GetMouse uses two VAR parameters for obtaining the current horizontal and vertical position of the mouse pointer.

Since we need to draw and erase the rubberbanding line, we use the two pen patterns of Black and White. This has the disadvantage of erasing whatever the line passes over, but you can’t have everything in a simple little program. The procedure PenPat sets the working pen pattern to the passed value.

DrawLine uses two points, this time in the form of four coordinates, to designate the starting and ending points of the line. DrawLine, of course, uses the current pen pattern.

Finally, after the mouse button is released, the rectangle is drawn with FrameRect. This is done with the pen pattern set to black. Since we don’t want to draw over the outline with subsequent FillRect calls, the procedure InsetRect is called to change the coordinates of the rectangle by one on each side, making it slightly smaller.

After the rectangle is drawn, the Fill_Rect procedure is called to fill it in. Note, please, that Fill_Rect is distinct from FillRect. Fill_Rect uses the calls Button, GetMouse, PtInRect, Random, and FillRect to perform its task. Button and GetMouse are used as before. PtInRect determines if the mouse is inside the new rectangle when the button is depressed.

A new pattern is created by calling the function Random eight times within a loop. Random returns a value from -32768 and 32767. Abs and Mod are used to bring the random number in the range 0..255. After the random pattern is created, FillRect is called to draw the pattern into the rectangle.

MODIFYING THE PROGRAM

The program runs forever, and the menu option Halt must be chosen to exit. In order to overcome this, you might want to modify the program to present you with a Black or Grey box (read rectangle) where you’d click the mouse to quit. Where in the program would you draw the rectangle? At what point or points would you have to check to see if it has been clicked? How will you handle rectangles that overlap your ‘exit’ box? These exercises are left to the student!

That’s it for this month. In the next column, we’ll further explore the powerful features of QuickDraw, and find out what makes it so unique and wonderful among graphic tools. We’ll also have another program that utilizes these terrific features. If you like our Pascal column or have programming ideas of your own to contribute, please feel free to write me care of MacTech. Ciao.

program MacTutor_QD_Demo;

{ This program will use the standard features of } {QuickDraw to introduce 
use of QuickDraw data} {structures and routine calls from MacPascal.} 

{ -- By Chris Derossi}

 var
  P1, P2, P3 : Point;
  WorkingRect : Rect;

 function Min (Num1, Num2 : integer) : integer;

{ return the minimum of the two numbers passed.}

 begin
  if Num1 < Num2 then
   Min := Num1
  else
    Min := Num2;
 end;

 function Max (Num1, Num2 : integer) : integer;

{ returns the maximum of two numbers passed.}

 begin
  if Num1 > Num2 then
  Max := Num1
  else
    Max := Num2;
 end;

 procedure Make_Rect (var theRect : Rect);

{ This is the first of the two main procedure. It} 
{allows the user to select diagonal corners of the} 
{rectangle to be drawn, using a ‘rubber band’ line.} 
{When the button is released, the recatangle is} 
{drawn.}

 begin
  repeat
   until Button;  {Wait till the button is pressed}
  GetMouse(P1.h, P1.v); {Where was the mouse?}
  P2 := P1;
  P3 := P1;
  while Button do  {update while button is down.}
   begin
      GetMouse(P3.h, P3.v);
    if (P2.h <> P3.h) or (P2.v <> p3.v) then  
 {the mouse has moved}
    begin
        PenPat(White);
      DrawLine(P1.h, P1.v, P2.h, P2.v);  
 {Erase the old line}
      PenPat(Black);
    DrawLine(P1.h, P1.v, P3.h, P3.v);  
 {Draw the new line}
    P2 := P3;
    end;
   end;

  PenPat(White);  {Erase line for the last time.}
  DrawLine(P1.h, P1.v, P2.h, P2.v);
  PenPat(Black);
  theRect.TopLeft.v := Min(P1.v, P2.v); 
  
{Set the rectangle, making sure}
  theRect.TopLeft.h := Min(P1.h, P2.h);   
{that the top is above the bottom}
  theRect.BotRight.v := Max(P1.v, P2.v); 
{and the left is less than the}
  theRect.BotRight.h := Max(P1.h, P2.h); {right.}

  FrameRect(theRect);   {Draw the rectangle}
  InsetRect(theRect, 1, 1);  
{Shrink it so that the pattern does not draw}
 {over the rectangle frame.}
 end;

 procedure Fill_Rect (theRect : Rect);

  var
   myPat : Pattern;
   Index : Integer;
   Done : Boolean;

 begin
  Done := False;
  while not Done do  
{continue until the mouse is outside of the}
   {new rectangle.}
   begin
    repeat
      until Button;   {Wait for the button}
    GetMouse(P1.h, P1.v);
    if PtInRect(P1, theRect) then  
{is the mouse in the rectangle?}
    begin
    for Index := 0 to 7 do
     myPat[Index] := Abs(Random) mod 256; {make a random pattern}
     FillRect(theRect, myPat);  {Fill the rectangle}
    end
    else
    Done := True;
   end; {While}
 end; {Fill_Rect}


begin  {Main Program}
 while true do
  begin
    Make_Rect(WorkingRect);
    Fill_Rect(WorkingRect);
  end;
end.   {Main}

 
AAPL
$101.79
Apple Inc.
+0.21
MSFT
$46.68
Microsoft Corpora
+0.16
GOOG
$589.27
Google Inc.
+4.50

MacTech Search:
Community Search:

Software Updates via MacUpdate

Xcode 6.0.1 - Integrated development env...
Apple Xcode is Apple Computer's integrated development environment (IDE) for OS X. The full Xcode package is free to ADC members and includes all the tools you need to create, debug, and optimize... Read more
Apple Safari 7.1 - Apple's Web brow...
Apple Safari in OS X Mavericks brings you all-new ways to find and enjoy the best of the web. It works with iCloud to give you a seamless browsing experience across all your devices. It looks out for... Read more
Delivery Status 6.1.2 - Check delivery s...
Delivery Status displays delivery status of packages for a variety of shipment services. Can't wait for your packages to arrive? Don't waste your time checking the site constantly, just open this all... Read more
Mavericks Cache Cleaner 8.0.9 - Clear ca...
Mavericks Cache Cleaner is an award-winning general purpose tool for OS X. MCC makes system maintenance simple with an easy point-and-click interface to many OS X functions. Novice and expert users... Read more
OneNote 15.2.2 - Free digital notebook f...
OneNote is your very own digital notebook. With OneNote, you can capture that flash of genius, that moment of inspiration, or that list of errands that's too important to forget. Whether you're at... Read more
Apple Configurator 1.6 - Configure and d...
Apple Configurator makes it easy for anyone to mass configure and deploy iPhone, iPad, and iPod touch in a school, business, or institution. Three simple workflows let you prepare new iOS devices... Read more
SpamSieve 2.9.16 - Robust spam filter fo...
SpamSieve is a robust spam filter for major email clients that uses powerful Bayesian spam filtering. SpamSieve understands what your spam looks like in order to block it all, but also learns what... Read more
OS X Server 3.2.1 - For OS X 10.9.5 Mave...
OS X Server is the next generation of Apple's award winning server software. Designed for OS X and iOS devices, OS X Server makes it easy to share files, schedule meetings, synchronize contacts, host... Read more
Apple Security Update 2014-004 - For OS...
Apple Security Update is recommended for all users and improves the security of Mac OS X. For information on the security content of this update, please visit this website: http://support.apple.com/... Read more
OS X Mavericks 10.9.5 - The latest versi...
Apple OS X Mavericks is the latest release of the world's most advanced desktop operating system. Now free! With more than 200 new features, OS X Mavericks brings Maps and iBooks to the Mac,... Read more

Latest Forum Discussions

See All

Down Among the Dead Men (Games)
Down Among the Dead Men 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Avast! Take to the high seas in a fully interactive piratical tale of broadsides and buccaneers. From author Dave... | Read more »
Sling Adds Chromecast Support Through Sl...
Sling Adds Chromecast Support Through Slingplaye​r Mobile Apps Posted by Jessica Fisher on September 18th, 2014 [ permalink ] | Read more »
How to Completely Delete Your iPhone’s C...
The iPhone 6 is out tomorrow, and plenty of people are excited about it. So much so that they’re planning to – or already have – traded in their old iPhone to go towards it. The thing about trading in hardware is it’s very important to make sure... | Read more »
Dragon Quest I Review
Dragon Quest I Review By Andrew Fisher on September 18th, 2014 Our Rating: :: THINE QUEST AWAITETHUniversal App - Designed for iPhone and iPad Its historical significance aside, Dragon Quest 1 is a fun, campy, difficult, thoroughly... | Read more »
It Came From Canada: Overkill 3
Overkill 3 is like every trope of big modern gaming rolled into one. It’s a sequel to an action-packed military shooter. It’s flashy and scripted and flaunts its sophisticated graphics. And it’s a mobile game with a heavy emphasis on in-app... | Read more »
New Modes and Leader Boards in Update fo...
New Modes and Leader Boards in Update for Rules! Posted by Jessica Fisher on September 18th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
TwistedRun Review
TwistedRun Review By Rob Thomas on September 18th, 2014 Our Rating: :: DON'T TWIST YOUR ANKLE!Universal App - Designed for iPhone and iPad TwistedRun is kind of like running up a giant curly fry into the sky. Or maybe that was just... | Read more »
Scope Review
Scope Review By Jennifer Allen on September 18th, 2014 Our Rating: :: LOCATION AWAREiPhone App - Designed for the iPhone, compatible with the iPad Want to easily find photos from around the world based on their location? Scope is a... | Read more »
HipstaFox Review
HipstaFox Review By Jordan Minor on September 18th, 2014 Our Rating: :: FANTASTIC MR. FOXUniversal App - Designed for iPhone and iPad HipstaFox is a great single that makes players long for the whole album.   | Read more »
Ninja Raft (Games)
Ninja Raft 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: ** Special Launch Price ** "Ninja Raft is definitely the game to play if you’re into Tower Defense games and want to play something... | Read more »

Price Scanner via MacPrices.net

Save up to $300 on the price of a new Mac wit...
Purchase a new Mac or iPad at The Apple Store for Education and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free,... Read more
13-inch 2.8GHz Retina MacBook Pro available f...
B&H Photo has the new 2014 13″ 2.8GHz Retina MacBook Pro on sale for $1699.99 including free shipping plus NY sales tax only. They’ll also include free copies of Parallels Desktop and LoJack for... Read more
16GB iPad Air on sale for $449, save $50
Walmart has the 16GB iPad Air WiFi on sale for $449 on their online store for a limited time. Choose free home shipping or free local store pickup. Their price represents a $50 savings over standard... Read more
13-inch 256GB MacBook Air on sale for $1099,...
B&H Photo has the 2014 13″ 1.4GHz 256GB MacBook Air on sale for $1099.99. Shipping is free, and B&H charges NY sales tax only. Their price is $100 off MSRP. Read more
Toshiba Introduces TransMemory ID High-Speed...
Toshiba’s Digital Products Division (DPD), a division of Toshiba America Information Systems, Inc., today introduced the TransMemory ID USB 3.0 Flash Drive, a simpler storage solution for people who... Read more
New iPads and OS X Yosemite Release Coming Oc...
The DailyDot’s Micah Singleton reports that Apple is planning to hold its next product announcement event on Oct. 21, at which it will unveil the iPad Air 2 and iPad mini 3 and release a final build... Read more
Logitech Bluetooth Multi-Device Cross-Platfor...
Logitech has an enviable track record of making some of the best computer keyboards and mice. At least in my estimation, the best freestanding keyboards I’ve ever used have been Logitech units,... Read more
Roundup of Apple refurbished iPad Airs and iP...
Apple is offering Certified Refurbished iPad Airs for up to $140 off MSRP. Apple’s one-year warranty is included with each model, and shipping is free. Stock tends to come and go with some of these... Read more
Sprint offers 16GB iPad mini for $199.99 with...
Sprint is offering 1st generation 16GB iPad minis for $199.99 with a 2-year service agreement. Standard MSRP for this iPad is $429. Their price is the lowest available for this model. Read more
2.5GHz Mac mini remains on sale for $549, sav...
B&H Photo has the 2.5GHz Mac mini on sale for $549.99 including free shipping. That’s $50 off MSRP, and B&H will also include a free copy of Parallels Desktop software. NY sales tax only. Read more

Jobs Board

Project Manager, *Apple* Financial Services...
**Job Summary** Apple Financial Services (AFS) offers consumers, businesses and educational institutions ways to finance Apple purchases. We work with national and Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.