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

Lyn 1.8.5 - Lightweight image browser an...
Lyn is a fast, lightweight image browser and viewer designed for photographers, graphic artists, and Web designers. Featuring an extremely versatile and aesthetically pleasing interface, it delivers... Read more
Apple iOS 10.2.1 - The latest version of...
iOS 10 is the biggest release of iOS ever. A massive update to Messages brings the power of the App Store to your conversations and makes messaging more personal than ever. Find your route with... Read more
Apple Security Update 2016-003 Supplemen...
Apple Security Update is recommended for all users and improves the security of OS X. For detailed information about the security content of this update, please visit: http://support.apple.com/kb/... Read more
Apple macOS Sierra 10.12.3 - The latest...
With Apple macOS Sierra, Siri makes its debut on Mac, with new features designed just for the desktop. Your Mac works with iCloud and your Apple devices in smart new ways, and intelligent... Read more
BetterTouchTool 1.992 - Customize Multi-...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more
Viber 6.5.5 - Send messages and make cal...
Viber lets you send free messages and make free calls to other Viber users, on any device and network, in any country! Viber syncs your contacts, messages and call history with your mobile device, so... Read more
Opera 42.0.2393.137 - High-performance W...
Opera is a fast and secure browser trusted by millions of users. With the intuitive interface, Speed Dial and visual bookmarks for organizing favorite sites, news feature with fresh, relevant content... Read more
iClock Pro 3.4.7 - Customize your menuba...
iClock Pro is a menu bar replacement clock for Apple's default clock. iClock Pro is an update, total rewrite and improvement to the popular iClock. Have the day, date and time in different fonts and... Read more
PhotoDesk 4.1.5 - Instagram client for p...
PhotoDesk lets you view, like, comment, and download Instagram pictures/videos. (NO Uploads! / Image Posting! Instagram forbids that! AND you need an existing Instagram account). But you can do so... Read more
Capo 3.5.1 - Slow down and learn to play...
Capo lets you slow down your favorite songs so you can hear the notes and learn how they are played. With Capo, you can quickly tab out your songs atop a highly-detailed OpenCL-powered spectrogram... Read more

Collect pets and sling arrows in Arcane...
Mobile gaming is a crowded market, but regular updates are a good way to keep us attention-short players keen. The brand new content in Arcane Online is a prime example. Published by Japanese developer Gala, Arcane Online is a fantasy MMO that... | Read more »
Super Mario Run dashes onto Android in M...
Super Mario Run was one of the biggest mobile launches in 2016 before it was met with a lukewarm response by many. While the game itself plays a treat, it's pretty hard to swallow the steep price for the full game. With that said, Android users... | Read more »
WarFriends Beginner's Guide: How to...
Chillingo's new game, WarFriends, is finally available world wide, and so far it's a refreshing change from common mobile game trends. The game's a mix of tower defense, third person shooter, and collectible card game. There's a lot to unpack here... | Read more »
Super Gridland (Entertainment)
Super Gridland 1.0 Device: iOS Universal Category: Entertainment Price: $1.99, Version: 1.0 (iTunes) Description: Match. Build. Survive. "exquisitely tuned" - Rock Paper Shotgun No in-app purches, and no ads! | Read more »
Red's Kingdom (Games)
Red's Kingdom 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Mad King Mac has kidnapped your father and stolen your golden nut! Solve puzzles and battle goons as you explore and battle your... | Read more »
Turbo League Guide: How to tame the cont...
| Read more »
Fire Emblem: Heroes coming to Google Pla...
Nintendo gave us our first look at Fire Emblem: Heroes, the upcoming mobile Fire Emblem game the company hinted at last year. Revealed at the Fire Emblem Direct event held today, the game will condense the series' tactical RPG combat into bite-... | Read more »
ReSlice (Music)
ReSlice 1.0 Device: iOS Universal Category: Music Price: $9.99, Version: 1.0 (iTunes) Description: Audio Slice Machine Slice your audio samples with ReSlice and create flexible musical atoms which can be triggered by MIDI notes or... | Read more »
Stickman Surfer rides in with the tide t...
Stickson is back and this time he's taken up yet another extreme sport - surfing. Stickman Surfer is out this Thursday on both iOS and Android, so if you've been following the other Stickman adventures, you might be interested in picking this one... | Read more »
Z-Exemplar (Games)
Z-Exemplar 1.4 Device: iOS Universal Category: Games Price: $3.99, Version: 1.4 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

Deal alert! 13-inch 2.0GHz MacBook Pros for $...
B&H Photo has the new 2016 13″ 2.0GHz non-Touch Bar MacBook Pros in stock today and on sale for $225 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.0GHz MacBook Pro... Read more
Free LibreOffice Portable 5.2.4 Complete Offi...
PortableApps.com and The Document Foundation have announce the release of LibreOffice Portable 5.2.4. LibreOffice Portable is an Open Source full-featured office suite — including a word processor,... Read more
Apple Planning Three New Tablets For 2017 – D...
Digitimes’ Rebecca Kuo and Joseph Tsai say that unnamed insider sources report Apple having three new tablets in the pipeline for 2017 release: a 9.7-inch model with a friendly price range, a new mid... Read more
Roundup of 15-inch Touch Bar MacBook Pro sale...
B&H Photo has the new 2016 15″ Apple Touch Bar MacBook Pros in stock today and on sale for up to $150 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 15″ 2.7GHz Touch Bar... Read more
Apple refurbished iPad Pros available for up...
Apple has Certified Refurbished 9″ and 12″ Apple iPad Pros available for up to $160 off the cost of new iPads. An Apple one-year warranty is included with each model, and shipping is free: - 32GB 9″... Read more
16GB iPad Air 2, Apple refurbished, available...
Apple has Certified Refurbished 16GB iPad Air 2s available for $319 including free shipping. A standard Apple one-year is included. Their price is $60 off original MSRP for this model. Read more
Apple iMacs on sale for up to $120 off MSRP
B&H Photo has 21″ and 27″ Apple iMacs on sale for up to $120 off MSRP, each including free shipping plus NY sales tax only: - 27″ 3.3GHz iMac 5K: $2199 $100 off MSRP - 27″ 3.2GHz/1TB Fusion iMac... Read more
Apple refurbished Apple TVs available for up...
Apple has Certified Refurbished 32GB and 64GB Apple TVs available for up to $30 off the cost of new models. Apple’s standard one-year warranty is included with each model, and shipping is free: -... Read more
Save up to $350 with Apple Certified Refurbis...
Apple has Certified Refurbished 2015 21″ & 27″ iMacs available for up to $350 off MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are available: - 21″ 3.... Read more
2015 12-inch Retina MacBooks, Apple refurbish...
Apple has Certified Refurbished 2015 12″ Retina MacBooks available for up to $410 off original MSRP. Apple will include a standard one-year warranty with each MacBook, and shipping is free. The... Read more

Jobs Board

*Apple* & PC Desktop Support Technician...
Apple & PC Desktop Support Technician job in Manhattan, NY Introduction: We have immediate job openings for several Desktop Support Technicians with one of our most Read more
*Apple* & PC Desktop Support Technician...
Apple & PC Desktop Support Technician job in Stamford, CT We have immediate job openings for several Desktop Support Technicians with one of our most well-known Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Site Security Manager - Apple (Unite...
# Apple Site Security Manager Job Number: 54692472 Culver City, California, United States Posted: Jan. 19, 2017 Weekly Hours: 40.00 **Job Summary** The Apple Read more
*Apple* macOS Systems Integration Administra...
…most exceptional support available in the industry. SCI is seeking an Junior Apple macOS systems integration administrator that will be responsible for providing Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.