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}

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Dashlane 6.2027.0 - Password manager and...
Dashlane is an award-winning service that revolutionizes the online experience by replacing the drudgery of everyday transactional processes with convenient, automated simplicity - in other words,... Read more
ffWorks 2.1.5 - Convert multimedia files...
ffWorks, focused on simplicity, brings a fresh approach to the use of FFmpeg, allowing you to create ultra-high-quality movies without the need to write a single line of code on the command-line.... Read more
Dropbox 101.4.434 - Cloud backup and syn...
Dropbox for Mac is a file hosting service that provides cloud storage, file synchronization, personal cloud, and client software. It is a modern workspace that allows you to get to all of your files... Read more
1Password 7.6 - Powerful password manage...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
EyeTV 4.0.0 - Watch and record TV on you...
EyeTV brings a rich TV experience to your Mac. Watch live TV on your Mac. Pause, rewind, and record whenever you want. EyeTV gives you powerful control over what you watch and how you watch it. Put... Read more
Tidy Up 5.3.7 - Find duplicate files and...
Tidy Up is a full-featured duplicate finder and disk-tidiness utility. Features: Supports Lightroom: it is now possible to search and collect duplicates directly in the Lightroom library. Multiple... Read more
Pinegrow 5.97 - Mockup and design web pa...
Pinegrow (was Pinegrow Web Designer) is desktop app that lets you mockup and design webpages faster with multi-page editing, CSS and LESS styling, and smart components for Bootstrap, Foundation,... Read more
BlueStacks 4.210.0 - Run Android applica...
BlueStacks App Player lets you run your Android apps fast and fullscreen on your Mac. Feature comparison chart How to install Bluestacks on your Mac Go to MacUpdate and click the green "Download"... Read more
WhatsApp 2.2027.10 - Desktop client for...
WhatsApp is the desktop client for WhatsApp Messenger, a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for... Read more
Art Text 4.0.1 - $29.99
Art Text is graphic design software specifically tuned for lettering, typography, text mockups and various artistic text effects. Supplied with a great variety of ready to use styles and materials,... Read more

Latest Forum Discussions

See All

Clash Royale: The Road to Legendary Aren...
Supercell recently celebrated its 10th anniversary and their best title, Clash Royale, is as good as it's ever been. Even for lapsed players, returning to the game is as easy as can be. If you want to join us in picking the game back up, we've put... | Read more »
Steam Link Spotlight - Disco Elysium
Steam Link Spotlight is a feature where we look at PC games that play exceptionally well using the Steam Link app. Our last entry was Signs of the Sojourner Read about how it plays using Steam Link over here. | Read more »
Distract Yourself With These Great Mobil...
There’s a lot going on right now, and I don’t really feel like trying to write some kind of pithy intro for it. All I’ll say is lots of people have been coming together and helping each other in small ways, and I’m choosing to focus on that as I... | Read more »
Pokemon Go's July Community Day wil...
Pokemon Go developers have announced the details concerning the upcoming Gastly Community Day. This particular event was selected by the players of the game after the Gas Pokemon came in second place after a poll that decided which Pokemon would... | Read more »
Clash Royale: The Road to Legendary Aren...
Supercell recently celebrated its 10th anniversary and their best title, Clash Royale, is as good as it's ever been. Even for lapsed players, returning to the game is as easy as can be. If you want to join us in picking the game back up, we've put... | Read more »
Detective Di is a point-and-click murder...
Detective Di is a point-and-click murder mystery set in Tang Dynasty-era China. You'll take on the role of China's best-known investigator, Di Renjie, as he solves a series of grisly murders that will ultimately lead him on a collision course with... | Read more »
Dissidia Final Fantasy Opera Omnia is se...
Dissidia Final Fantasy Opera Omnia, one of Square Enix's many popular mobile RPGs, has announced a plethora of in-game events that are set to take place over the summer. This will include several rewards, Free Multi Draws and more. [Read more] | Read more »
Sphaze is a neat-looking puzzler where y...
Sphaze is a neat-looking puzzler where you'll work to guide robots through increasingly elaborate mazes. It's set in a visually distinct world that's equal parts fantasy and sci-fi, and it's finally launched today for iOS and Android devices. [... | Read more »
Apple Arcade is in trouble
Yesterday, Bloomberg reported that Apple is disappointed in the performance of Apple Arcade and will be shifting their approach to the service by focusing on games that can retain subscribers and canceling other upcoming releases that don't fit... | Read more »
Pixel Petz, an inventive platform for de...
Pixel Petz has built up a sizeable player base thanks to its layered, easy-to-understand creative tools and friendly social experience. It revolves around designing, trading, and playing with a unique collection of pixel art pets, and it's out now... | Read more »

Price Scanner via MacPrices.net

B&H Photo offers $200-$300 discounts on A...
B&H Photo has new 16″ MacBook Pros on sale today for $200-$300 off Apple’s MSRP, starting at $2149. Expedited shipping is free to many addresses in the US: – 2019 16″ 2.6GHz 6-Core MacBook Pro... Read more
Clearance 2019 15″ MacBook Pros on sale today...
Amazon-owned Woot is blowing out Apple refurbished, clearance 2019 15″ MacBook Pros starting at only $1579 and up to $950 off Apple’s original MSRP. According to Woot, “These MacBooks are Refurbished... Read more
Apple Refurbished iMac Pros available for $35...
Amazon-owned Woot is selling Apple refurbished 27″ 3.2GHz 8-Core iMac Pros for $3599.99 shipped. That’s $1400 off Apple’s original MSRP for this model. According to Woot, these iMac Pros are “Factory... Read more
Clearance 2019 13″ 2.4GHz/256GB MacBook Pro o...
B&H Photo has dropped their price on the clearance 2019 13″ 2.4GHz/256GB Quad-Core Silver MacBook Pro by $500 off Apple’s original MSRP to a new low of only $1299. Expedited shipping is free to... Read more
$219 Apple AirPods Pro are back at Verizon, s...
Verizon has Apple AirPods Pro on sale again for a limited time for $219.99 on their online store. Their price is $30 off Apple’s MSRP, and it’s the lowest price we’ve seen for AirPods Pro. Available... Read more
Apple’s $779 13″ MacBook Air deal returns to...
Apple has clearance, Certified Refurbished, 2019 13″ MacBook Airs available again starting at $779. Each MacBook features a new outer case, comes with a standard Apple one-year warranty, and is... Read more
$200 13″ MacBook Pro discounts are back at Am...
Amazon has 2020 13″ 2.0GHz MacBook Pros on sale again today for $150-$200 off Apple’s MSRP. Shipping is free. Be sure to purchase the MacBook Pro from Amazon, rather than a third-party seller, and... Read more
Deal Alert! Apple AirPods with Wireless Charg...
Sams Club has Apple AirPods with Wireless Charging Case on sale on their online store for only $149.98 from July 6, 2020 to July 9, 2020. Their price is $50 off Apple’s MSRP, and it’s the lowest... Read more
Xfinity Mobile promo: Apple iPhone XS models...
Take $300 off the purchase of any Apple iPhone XS model at Xfinity Mobile while supplies last. Service plan required: – 64GB iPhone XS: $599.99 save $300 – 256GB iPhone XS: $749.99 save $300 – 512GB... Read more
New July 2020 promo at US Cellular: Switch an...
US Cellular has introduced a new July 2020 deal offering free 64GB Apple iPhone 11 smartphones to customers opening a new line of service. No trade-in required, and discounts are applied via monthly... Read more

Jobs Board

Product Manager, *Apple* Commercial Sales -...
Product Manager, Apple Commercial Sales Austin, TX, US Requisition Number:77652 As an Apple Product Manager for the Commercial Sales team at Insight, you Read more
Physical Therapist Assistant - *Apple* Hill...
Physical Therapist Assistant - Apple Hill Rehab - Full Time Tracking Code 62519 Job Description General Summary: Under the direct supervision of a licensed Physical Read more
Operating Room Assistant, *Apple* Hill Surg...
Operating Room Assistant, Apple Hill Surgical Center - Full Time, Day Shift, Monday - Saturday availability required Tracking Code 62363 Job Description Operating Read more
Perioperative RN - ( *Apple* Hill Surgical C...
Perioperative RN - ( Apple Hill Surgical Center) Tracking Code 60593 Job Description Monday - Friday - Full Time Days Possible Saturdays General Summary: Under the Read more
Product Manager, *Apple* Commercial Sales -...
Product Manager, Apple Commercial Sales Austin, TX, US Requisition Number:77652 As an Apple Product Manager for the Commercial Sales team at Insight, you Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.