TweetFollow Us on Twitter

Arrowheads
Volume Number:1
Issue Number:9
Column Tag:C WORKSHOP

How to Draw Arrowheaded Lines

How to Draw Arrowheaded Lines

While writing a new application, I discovered I needed to have lines with arrowheads (like the ones we all love in MacDraw). Not only that, I needed to have the line stop on the surface of an object (usually an oval or rectangle).

The first place to look, of course, is to see how MacDraw did it. After using MacDraw for some time in various applications, I was surprised to see that the arrowheads were not 3-pointed polygons but actually small wedges! This was discovered after placing an arrowhead on a thick line and noticing the curvature of the arrowhead.

Keeping with the Macintosh spirit, I decided to make the call similar to the ones used in QuickDraw (i.e. - Line and LineTo). Instead of using a LineTo call, this routine may be substituted and all of the LineTo's changed to ArrowLineTo's.

The parameter passed to it is the absolute horizontal and vertical coordinates of the end point of the line (as in LineTo). The end point is also where the arrowhead will be drawn.

The basic algorithm is simple -

1). Compute the slope of the line

2). Draw the line

3). Point the wedge in the opposite direction of the line (to create the effect of an arrowhead).

4). Draw the wedge

There is a fantastic Mac routine called PtToAngle that will compute the angle for you! All you need to do is to place a rectangle around the starting point, make the call, and the angle is returned to you (in degrees)!

The following code (written in Mac C) is pretty much self explanatory. You could experiment with the constants arrowWidth and arrowLength (as shown in Fig. 1) to vary the width and length of the arrowhead. Note - this routine could be changed so that these constants are passed as parameters, for applications that need varying sizes of arrowheads.

/************************************************************************

         ArrowLineTo.c

 Copyright 1985, FlottWare

 ************************************************************************/

#include "MacCDefs.h"// Mac ROM data structure definitions
#include "Events.h"
#include "Window.h"

extern struct P_Str *CtoPstr();
int strlen(str) char *str;
  {int i=0; while (str[i++]); return i-1;}
  
/*------------------------------------------------------------------------
    Global Data
   ------------------------------------------------------------------------*/
 
#define False 0
#define True 0xFF

Rect      windowRect = {40,4,336,508}; // Window Rectangle
WindowPtr windowPtr; // Window Pointer

EventRecord event; // Current event record

/*------------------------------------------------------------------------
    main()
   ------------------------------------------------------------------------*/
 
main()
  { 
  
  if (CatchSignal()) // Is the user quitting this application?
    ExitToShell(); // Go to Finder when done
    
  init(); // Init Mac 
 
  while (True)   // Poll events forever 
    { 
    SystemTask();// Perform System duties
    
    if (GetNextEvent(everyEvent, &event))    // Get the next event 
      {
      
      switch ( event.what ) // Which event is it? 
 {

 case autoKey:
 case keyDown:                         // Key was pressed 
 case mouseDown: // Mouse Button pressed 
   {
          Signal("All Done"); // Y - quit application
   break;
   } // case autoKey,keyDown,mouseDown:
   
 } // switch (event.what)      
      } // if (Getevent)
    } // while (true)
  } // main
  
/************************************************************************ 

   Windows
 ***********************************************************************/ 

 
/*---------------------------------------------------------------------- 
 
   init() -   
  ----------------------------------------------------------------------*/

init()
  {
   // Open a window
   
  windowPtr = NewWindow(0,&windowRect,CtoPstr("Hit Key or Mouse to Quit "),True,
                             documentProc,-1,True,0);
  SetPort(windowPtr);
  
  #define centerH 250
  #define centerV 150
  #define offset   50
   // Draw some lines with arrowheads
   
  MoveTo(centerH,centerV);
  ArrowLineTo(centerH-offset,centerV);
  
  MoveTo(centerH,centerV);
  ArrowLineTo(centerH-offset,centerV+offset);
  
  MoveTo(centerH,centerV);
  ArrowLineTo(centerH,centerV+offset);
  
  MoveTo(centerH,centerV);
  ArrowLineTo(centerH+offset,centerV+offset);
  
  MoveTo(centerH,centerV);
  ArrowLineTo(centerH+offset,centerV);
  
  MoveTo(centerH,centerV);
  ArrowLineTo(centerH+offset,centerV-offset);
  
  MoveTo(centerH,centerV);
  ArrowLineTo(centerH,centerV-offset);
  
  MoveTo(centerH,centerV);
  ArrowLineTo(centerH-offset,centerV-offset);
  
  } // end init()

/*----------------------------------------------------------------------
      ArrowLineTo(horiz,vert)
   
     This routine draws a line from the current pen location
 to point (h,v) with an arrowhead (wedge) on the end of it.
 
        Inputs : horiz       - horizontal coord of end point
                 vert        - vertical   coord of end point
  
 Written by: Rick Flott                           Mac C (Consulair) V 
1.0
 ----------------------------------------------------------------------*/

ArrowLineTo(horiz,vert)
  short horiz;
  short vert;
  {
   // Size of starting Rect used in PtToAngle
  #define rectOffset  30
   // Arrowhead (wedge) constants
 //   arrowWidth - width of 1/2 arrowhead (in degrees)
   //   arrowLength - length of arrowhead in pixels
  #define arrowWidth  25
  #define arrowLength 10
  
 // Rects used in angle calculations
  Rect  startRect; //   starting Rect used in PtToAngle
  Rect  arrowheadRect;    //   the Rect that the wedge is drawn in

  short arrowAngle;// Angle of arrowhead (in degrees)          
 
  
  Point startPt,endPt;    // Start,End points of line
  
  GetPen(&startPt);// Get the current pen location
 // Set up a rectangle around the starting point
   //    (this is needed for the PtToAngle routine)
  SetRect (&startRect,startPt.h - rectOffset,
                      startPt.v - rectOffset,
                      startPt.h + rectOffset,
       startPt.v + rectOffset);
       
  SetPt(&endPt,horiz,vert); // Set up the end point
    
   // Calculate the angle (in degrees) of the line segment
  PtToAngle(&startRect,&endPt,&arrowAngle);
   
  LineTo(horiz,vert);// Draw the line
  
  arrowAngle -= (180 + arrowWidth);// Create a arrowhead with a wedge 
facing the opposite direction

   // Set up a Rect for the wedge around the endpoint
  SetRect (&arrowheadRect,endPt.h - arrowLength,
                          endPt.v - arrowLength,
                          endPt.h + arrowLength,
           endPt.v + arrowLength);
     
        // Draw arrow head (a reversed wedge)
  PaintArc(&arrowheadRect,arrowAngle,2*arrowWidth);
  
  } // end ArrowLineTo()
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Unite 3 3.1 - Turn websites into full-fe...
Unite 3 lets you turn websites into apps on your Mac and change the way you use your computer forever Creating your app It all starts with the new Unite creation tool. Simply enter a name for your... Read more
App Tamer 2.5.2 - Efficiently manage you...
App Tamer tames your processor-monopolizing apps and keeps them from chewing up excessive CPU time and battery life. Powered by a unique AutoStop feature, App Tamer stops each application when you... Read more
Sid Meier's Civilization IV 1.74 -...
Note: Sid Meier's Civilization IV is no longer under development and the developer provides no support for it. With Civilization IV, history as you know it, is history. Rule throughout time and... Read more
Day One 4.15.3 - Maintain a daily journa...
Day One is an easy, great-looking way to use a journal / diary / text-logging application. Day One is well designed and extremely focused to encourage you to write more through quick Menu Bar entry,... Read more
Backblaze 7.0.1.450 - Online backup serv...
Backblaze is an online backup service designed from the ground-up for the Mac. With unlimited storage available for $6 per month, as well as a free 15-day trial, peace of mind is within reach with... Read more
Visual Studio Code 1.47.0 - Cross-platfo...
Visual Studio Code provides developers with a new choice of developer tool that combines the simplicity and streamlined experience of a code editor with the best of what developers need for their... Read more
Apple Pages 10.1 - Apple's word pro...
Apple Pages is a powerful word processor that gives you everything you need to create documents that look beautiful. And read beautifully. It lets you work seamlessly between Mac and iOS devices, and... Read more
Shimo 5.0.2 - VPN client for everyone.
Shimo is the most versatile VPN client for OS X and it enables really everybody to master secure network. It supports more protocols than any other VPN application out there! CiscoVPN, AnyConnect,... Read more
Yasu 6.0.1 - System maintenance app.
Note: Yasu is not being sold anymore and is listed only for people who had purchased it in the past. Yasu was created with system administrators who service large groups of workstations in mind, Yasu... Read more
Keynote 10.1 - Apple's presentation...
Easily create gorgeous presentations with the all-new Keynote, featuring powerful yet easy-to-use tools and dazzling effects that will make you a very hard act to follow. The Theme Chooser lets you... Read more

Latest Forum Discussions

See All

Puzzle & Dragons welcomes the cast o...
Puzzle & Dragons has a history of wild crossovers, and its latest is no exception. The gates of hell are now open, and the cast of Devil May Cry have made their grand entrance into the world Puzzle & Dragons. The collaboration is set to... | Read more »
Meteorfall: Krumit's Tale is launch...
Meteorfall: Krumit's Tale is getting an iOS & Android beta test this Thursday, and you can sign up now to get involved. [Read more] | Read more »
Marvel Duel, NetEase's promising ca...
Marvel Duel, NetEase's collectable card battler, has now opened for pre-registration in Thailand, Indonesia, Malaysia, and the Philippines. [Read more] | Read more »
PUBG Mobile teams up with Yamaha for a l...
PUBG Mobile has had various collaborations with various companies since it first burst onto the scene. The latest sees the popular battle royale title teaming up with vehicle and marine products company Yamaha, meaning players can take one of... | Read more »
Marvel Super War launches its third seas...
Marvel Super War, NetEase's popular MOBA, has kicked off its third season today, introducing its Zone Invasion beta and an all-new playable superhero. [Read more] | Read more »
Brave Dungeon, Unlock Games' idle-R...
Brave Dungeon, Unlock Games' idle-RPG and auto chess title, has been downloaded over 1 million times since it launched last week. To commemorate reaching this milestone the developers have decided to host a series of in-game events. [Read more] | 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 »
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 »

Price Scanner via MacPrices.net

Apple has 2020 13″ 4-Core MacBook Airs availa...
Apple has a full line of Certified Refurbished 2020 13″ 4-Core MacBook Airs available for $200 off the cost of new models. Each MacBook features a new outer case, comes with a standard Apple one-year... Read more
Apple restocks clearance 2019 13″ MacBook Pro...
Apple has restocked Certified Refurbished 2019 13″ 1.4GHz 4-Core Touch Bar MacBook Pros starting at $979 and up to $440 off original MSRP. Apple’s one-year warranty is included, shipping is free, and... Read more
US Cellular offers $300 off any new Cellular...
US Cellular is offering a $300 discount on any new Cellular Apple iPad, iPad Air, iPad Pro, or iPad mini with a new line of service. According to US Cellular, “Promotional pricing requires purchase... Read more
Sale! 16″ MacBook Pros for $400 off Apple’s M...
Amazon has 16″ MacBook Pros on sale for $400 off Apple’s MSRP today with prices starting at $1999. Shipping is free: – 2019 16″ 2.6GHz 6-Core MacBook Pro Space Gray: $1999.99 $400 off MSRP – 2019 16... Read more
Lowest price ever: Apple AirPods Pro for $214...
Amazon-owned Woot has new Apple AirPods Pro on sale for today only (Monday, July 13th) for $214.99 including free shipping for Prime members. Their price is $35 off Apple’s MSRP, and it’s the lowest... Read more
Woot is selling refurbished Apple iPhones tod...
Amazon-owned Woot is selling refurbished unlocked Apple iPhones today for as low as $99. Shipping is free for prime members. The following models are available, and note that many will sell out... Read more
Take $50 off the 64GB Apple iPhone SE at Simp...
Use coupon code SUMMER2020 at Simple Mobile through July 31, 2020, and take 20% off the 64GB Apple iPhone SE + service plan. This is in addition to their standard $50 discount on the iPhone SE.... Read more
Weekend Sale: Woot offers clearance MacBook,...
Amazon-owned Woot is blowing out a wide range of MacBooks, MacBook Airs, and MacBook Pros starting at only $389. All models are open-box returns, and according to Woot, “these MacBooks are in New-... Read more
Apple’s 2020 Mac minis on sale for up to $100...
B&H Photo has Apple’s 2020 Mac minis on sale today for $40-$100 off MSRP, each including free expedited delivery for many US addresses. These are the same Mac minis sold by Apple in their retail... Read more
Apple restocks refurbished 10.5″ iPad Airs fo...
Apple has restocked 10.5″ WiFI iPad Airs models for up to $100 off MSRP, Certified Refurbished. Each iPad comes with Apple’s standard one-year warranty and includes a new outer case. Shipping is free... Read more

Jobs Board

Blue *Apple* Cafe Student Worker - Fall - P...
…to enhance your work experience. Student positions are available at the Blue Apple Cafe. Employee meal discount during working hours is provided. Duties include food Read more
Geek Squad Advanced Repair *Apple* Professi...
**769390BR** **Job Title:** Geek Squad Advanced Repair Apple Professional **Job Category:** Store Associates **Store Number or Department:** 000580-Reading-Store Read more
Executive Team Leader GM Sales (Assistant Man...
…(Assistant Manager General Merchandise and Operations) - Apple Valley, CaliforniaApply NowJob ID:R0000082364job family:Store Managementschedule:Full Read more
Executive Team Leader Assets Protection (Assi...
…Assets Protection (Assistant Manager Loss Prevention) - Apple Valley, CaliforniaApply NowJob ID:R0000082365job family:Store Managementschedule:Full Read more
*Apple* Computing Sales Professional - Best...
**768543BR** **Job Title:** Apple Computing Sales Professional **Job Category:** Store Associates **Store Number or Department:** 002509-Riverdale-Store **Job Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.