TweetFollow Us on Twitter

Mar 94 Challenge
Volume Number:10
Issue Number:3
Column Tag:Programmers’ Challenge

Related Info: Color Quickdraw

Programmers’ Challenge

By Mike Scanlin, MacTech Magazine Regular Contributing Author

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

The rules

Here’s how it works: Each month there will be a different programming challenge presented here. First, you must write some code that solves the challenge. Second, you must optimize your code (a lot). Then, submit your solution to MacTech Magazine (formerly MacTutor). A winner will be chosen based on code correctness, speed, size and elegance (in that order of importance) as well as the postmark of the answer. In the event of multiple equally desirable solutions, one winner will be chosen at random (with honorable mention, but no prize, given to the runners up). The prize for the best solution each month is $50 and a limited edition “The Winner! MacTech Magazine Programming Challenge” T-shirt (not to be found in stores).

In order to make fair comparisons between solutions, all solutions must be in ANSI compatible C (i.e., don’t use Think’s Object extensions). Only pure C code can be used. Any entries with any assembly in them will be disqualified (except for those challenges specifically stated to be in assembly). However, you may call any routine in the Macintosh toolbox you want (i.e., it doesn’t matter if you use NewPtr instead of malloc). All entries will be tested with the FPU and 68020 flags turned off in THINK C. When timing routines, the latest version of THINK C will be used (with ANSI Settings plus “Honor ‘register’ first” and “Use Global Optimizer” turned on) so beware if you optimize for a different C compiler. All code should be limited to 60 characters wide. This will aid us in dealing with e-mail gateways and page layout.

The solution and winners for this month’s Programmers’ Challenge will be published in the issue two months later. All submissions must be received by the 10th day of the month printed on the front of this issue.

All solutions should be marked “Attn: Programmers’ Challenge Solution” and sent to Xplain Corporation (the publishers of MacTech Magazine) via “snail mail” or preferably, e-mail - AppleLink: MT.PROGCHAL, Internet: progchallenge@xplain.com, CompuServe: 71552,174 and America Online: MT PRGCHAL. If you send via snail mail, please include a disk with the solution and all related files (including contact information). See page 2 for information on “How to Contact Xplain Corporation.”

MacTech Magazine reserves the right to publish any solution entered in the Programming Challenge of the Month and all entries are the property of MacTech Magazine upon submission. The submission falls under all the same conventions of an article submission.

BITMAP TO TEXT

Have you ever seen one of those text files where if you print it out, tack it on a wall and step back it looks like a graphic? I’ve seen dragons, islands, Star Trek images, etc. done this way. This month’s challenge is to write the routine that converts a bitmap into a text equivalent.

The prototype of the function you write is:


/* 1 */
short BitMapToText(bitMapPtr, fontName,
  fontSize, outputFile)
BitMap  *bitMapPtr;
Str255  fontName;
unsigned short fontSize;
FILE    *outputFile;

BitMapPtr points to the input bits. The max size is 1000 pixels square. fontname is the name of the monospaced font to use (Monaco, Courier, for example) and fontSize is the size of that font that should be used (6pt to 24pt). outputFile is a standard C output stream that you should write your text output to, each line separated by a 0x0D byte. The return value of the function is an error code: zero if nothing went wrong or non-zero if an error occurred. Do not close outputFile when you are finished.

Your basic strategy will be to split the bitMap into character size pieces and then find the best character match for each piece. You should only use the printable ASCII characters (charCodes from 32 to 127, inclusive). The closeness-of-match algorithm is not given. It’s up to you to pick something that works reasonably well and doesn’t take 50 years to compute. This contest will be judged primarily on speed but routines that produce unrecognizable output will be disqualified (no matter how fast they are). Recognizability will be judged on the screen, at 72dpi.

Note that in order to have recognizable output the size of the smallest detail in the input image needs to be roughly equal to or larger than a single character of the given font and font size. This will be true for the test images I use (so don’t stress too much over the problem of how to represent a very small image using only 24pt glyphs).

TWO MONTHS AGO WINNER

Of the eight entries I received for the Connect The Dots challenge, six worked correctly. Bill Karsh (Chicago, IL) joins the ranks of Challenge superstars for coming in first place for the second time. Bill previously won the Who Plays Who challenge and is now tied in a 4-way tie for the most number of Challenge wins. Bill’s line drawing routine is about 3x faster than Color QuickDraw for long lines and about 30x faster for very short lines (for the special cases given in the challenge: no clipping, pen size (1, 1), patCopy, no bitMaps). If you have intensive line-drawing routines in your code you ought to consider casing out those cases that Bill’s code handles and using it instead of many calls to Line or LineTo.

Here are the code sizes and average times (for medium to long line-length tests) of each entry. Numbers in parens after a person’s name indicate how many times that person has finished in the top 5 places of all previous Programmer Challenges, not including this one:

Name Time Code

Bill Karsh (2) 1114 1314

Kevin Cutts (2) 1370 1802

Bob Boonstra (5) 1434 750

Allen Stenger (2) 1623 1664

John Heaney 1711 710

Stefan Pantke 2500 876

Color Quickdraw 3219 ?

There were three cases that had to be dealt with: 8-bit, 16-bit and 32-bit deep pixMaps. Once the appropriate pixel value to stuff has been figured out, all three cases are the same (as far as determining which pixels are part of the line). Bill solved this redundant code problem by having the guts of each case #included in three different places. This makes it easy to update the line generating code for all three cases at the same time. And as did nearly everyone else, Bill handles the common cases of horizontal and vertical lines separately (which is a big win for those cases).

For the 8-bit case he uses his own RGB2Index routine instead of the ROM’s Color2Index, which would be fine if his routine worked all the time, but it doesn’t. It only works if the RGB value you’re trying to convert is an exact match with one of the index values. However, the main point of this challenge was about drawing lines fast, not inverse color table lookups.

Kevin Cutts (Schaumburg, IL) and Bob Boonstra (Westford, MA) deserve a mention here because in some of the very short line cases their code was faster than Bill’s. But I think the average line drawn by QuickDraw is longer than a few pixels and Bill’s code is faster for those cases so he wins.

I’d also like to apologize to Alan Hughes (Ames, IA) for the mixup last month that caused his on-time and correct entry to the Present Packing Challenge to get to me after I had sent in the column. His 94.2 average puts him in 3rd place and knocks Dave Darrah out of the top 5.

As readers of this column know, I have been stressing 680x0 optimizations in this column for over a year (and C code that generates better 680x0 code in Think C). Now that the PowerPC is coming out I am faced with a choice: Which platform should I run the challenge on, 680x0 or 601? Obviously, if there is a switch to 601 it would not happen for at least a couple of months after they are made generally available. But are readers interested in 601 tricks or should we stick to the installed base of 680x0s for many more months? And if and when we switch to the 601, what PPC compiler should I use to test challenge entries? Send me e-mail at the progchal addresses in the front of the magazine and let me know what you think. Thanks.

Here’s Bill’s winning solution:

ConnectTheDots

Response to Jan 94 MacTech Programmer's Challenge.

Object: Go around QD to draw color lines as fast as possible.

Specs:

• nDots >= 2,

• handle only cases {(pixelSize,cmpSize,cmpCount) = (8,8,1), (16,5,3), (32,8,3)},

• arbitrary alpha-bits,

• don't bother clipping,

• penSize = 1,1,

• patCopy mode.

Notes on method: Specify segment by two endpoints {(x,y)=(a,b),(A,B)}. Form of line is {(x,y): (y-b)/(x-a) = m}, where slope m = (B-b)/(A-a). Then, y = m*(x-a)+b.

Two successive values of y are: y2 = m*(x2-a)+b; y1 = m*(x1-a)+b, and the diff is, y2-y1 = m, since x2-x1 will always = 1 (pixel).

Therefore, as we move from x to x, we add or sub m to the previous value of y.

Speed: The cases that arise for combinations of {dy,dx} fall generally into 8 octants that cover the plane. Diagonally opposite octants are treated together, so there are 4 main cases to worry about. We first weed out 3 special cases: exactly horizontal, vertical, and diagonal segs. These are the simplest, most common, and fastest.

In a given octant, one of |dx|, |dy| is strictly larger than the other. Our loop over pixels will always be over the larger magnitude for higher resolution drawing. The slope is formed then by smallNum/largeNum which must have quotient == 0, and remainder == smallNum. Adding the slope is a matter of accumulating remainders. If this sum exceeds largeNum, we move to next pixel.


/* 2 */
#pragma options( honor_register, !assign_registers )
#pragma options( !check_ptrs )

#include"ConnectTheDots.h"

#define HiFiveMask 0xF800
#define Abs( a ) (a > 0 ? a : -a)

/* RGB2Index
 *
 * Expects rgb color is an exact member of table, to avoid time spent 
close
 * matching. Index is just position in table.
 */
static Byte RGB2Index( ColorSpec *cSpec, RGBColor *rgb )
{
 register ColorSpec*cs = cSpec;
 register short  entries = ((short*)cs)[-1]+1;
 register short  red = rgb->red,
 green = rgb->green,
 blue = rgb->blue;
 do {
 if( red   == cs->rgb.red  &&
 blue  == cs->rgb.blue &&
 green == cs->rgb.green )
 return cs-cSpec;
 ++cs;
 } while( --entries );
}
/* Lines8
 *
 * Depth == 8 case.
 *
 * To maximize register usage, chose to put rowBytes in address reg. 
 
 * Also, some vars like v_Cnt are dual purpose.
 */
static void Lines8(
 PixMapPtrpm,
 Point  dot[],
 unsigned short  nDots,
 register Byte   pixel )
{
 register Ptr  at;
 #include "ConnectTheDots.com"
}

/* Lines16
 */
static void Lines16(
 PixMapPtrpm,
 Point  dot[],
 unsigned short  nDots,
 register short  pixel )
{
 register short  *at;
 #include "ConnectTheDots.com"
}

/* Lines32
 *
 * align ensures 4-byte stack alignment for better speed.
 */
static void Lines32(
 PixMapPtrpm,
 Point  dot[],
 unsigned short  nDots,
 short  align,
 register long   pixel )
{
 register long   *at;
 #include "ConnectTheDots.com"
}

/* ConnectTheDots */
void ConnectTheDots(
 unsigned short  nDots,
 Point  dot[],
 PixMapHandle    pmH,
 RGBColor color )
{
 register PixMapPtrpm = *pmH;
 register unsigned short  pix16;
 register Ptr    p32;
 long   pix32;
 
 if( pm->pixelSize == 8 ) {
 
 Lines8( pm, dot, nDots,
 RGB2Index(&(**pm->pmTable).ctTable, &color) );
 }
 if( pm->pixelSize == 16 ) {

 pix16  = (color.red   & HiFiveMask) >> 1;
 pix16 |= (color.green & HiFiveMask) >> 6;
 pix16 |= (color.blue  & HiFiveMask) >> 11;
 
 Lines16( pm, dot, nDots, pix16 );
 }
 if( pm->pixelSize == 32 ) {
 
 p32 = ((Byte*)&pix32) + 1;
 *p32++ = *(Byte*)&color.red;
 *p32++ = *(Byte*)&color.green;
 *p32++ = *(Byte*)&color.blue;
 
 Lines32( pm, dot, nDots, 0, pix32 );
 }
}

This is the part of the line drawing algorithm common to all three depths, and it’s in its own separate file called ConnectTheDots.com. This is an unusual, but very useful way to use #include directive. Treat this file like a .h file, though it contains code instead of interface info. That means, like a .h file, you do not directly compile or link this file. If using Think C, don't put it in your project. It automatically becomes part of the .c file at compile time.

/* 3 */
/* ConnectTheDots.com
*/

// start
 register Ptr    rowBytes;
 register short  *pnt;
 register short  dh, dv, h_Sum, v_Cnt;
 Ptr    savedRowBytes;
 short  *savedPnt;
 short  pad;
 
 --nDots;
 
 pnt = (short*)dot;
 savedRowBytes = (Ptr)(pm->rowBytes & 0x7fff);

 do {

 // find this seg's dimensions {dv,dh} and endpoints in bounds coordinate
 // system.  ends are (v,h) and (v+dv,h+dh).
 // point to pixels, and restore rowBytes, which are altered in loop.

 dv       = *pnt++;
 dh       = *pnt++;
 v_Cnt    = *pnt;
 h_Sum    = pnt[1];
 dv      -= v_Cnt;
 dh      -= h_Sum;
 v_Cnt   -= pm->bounds.top;
 h_Sum   -= pm->bounds.left;
 at       = pm->baseAddr;
 rowBytes = savedRowBytes;
 
 if( !dh ) {
 // do vertical line
 if( dv < 0 ) {
 v_Cnt += dv;
 dv = -dv;
 }

 at = (Ptr)at + (long)v_Cnt*(short)rowBytes;
 at += h_Sum;
 
 v_Cnt = dv + 1;
 
doVert:
 do {
 *at = pixel;
 at = (Ptr)at + (long)rowBytes;
 } while( --v_Cnt );
 }
 else if( !dv ) {
 
 // do horizontal line
 
 if( dh < 0 ) {
 h_Sum += dh;
 dh = -dh;
 }
 
 at = (Ptr)at + (long)v_Cnt*(short)rowBytes;
 at += h_Sum;
 
 ++dh;
 
 do {
 *at++ = pixel;
 } while( --dh );
 }
 else if( Abs( dv ) >= Abs( dh ) ) {
 
 // more vertical or diagonal
 
 if( dv < 0 ) {
 v_Cnt += dv;
 h_Sum += dh;
 dv = -dv;
 dh = -dh;
 }
 
 at = (Ptr)at + (long)v_Cnt*(short)rowBytes;
 at += h_Sum;
 
 v_Cnt = dv + 1;
 
 if( dh == dv ) {
 rowBytes += sizeof(pixel);
 goto doVert;
 }
 else if( -dh == dv ) {
 rowBytes -= sizeof(pixel);
 goto doVert;
 }
 else {

 h_Sum = 0;
 
 savedPnt = pnt;
 pnt = (short*)sizeof(pixel);
 
 if( dh < 0 ) {
 dh = -dh;
 pnt = (short*)-sizeof(pixel);
 }

 do {
 *at = pixel;
 at = (Ptr)at + (long)rowBytes;
 
 h_Sum += dh;
 
 if( h_Sum >= dv ) {
 h_Sum -= dv;
 at = (Ptr)at + (long)pnt;
 }
 } while( --v_Cnt );
 
 pnt = savedPnt;
 }
 }
 else {
 
 // more horizontal
 
 if( dh < 0 ) {
 v_Cnt += dv;
 h_Sum += dh;
 dv = -dv;
 dh = -dh;
 }
 
 at = (Ptr)at + (long)v_Cnt*(short)rowBytes;
 at += h_Sum;
 
 v_Cnt = dh + 1;
 h_Sum = 0;

 if( dv < 0 ) {
 dv = -dv;
 rowBytes = (Ptr)(-(short)rowBytes);
 }
 
 do {
 *at++ = pixel;
 
 h_Sum += dv;
 
 if( h_Sum >= dh ) {
 h_Sum -= dh;
 at = (Ptr)at + (long)rowBytes;
 }
 } while( --v_Cnt );
 }
 } while( --nDots );
 
// end







  
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

CrossOver 14.1.3 - Run Windows apps on y...
CrossOver can get your Windows productivity applications and PC games up and running on your Mac quickly and easily. CrossOver runs the Windows software that you need on Mac at home, in the office,... Read more
Little Snitch 3.5.3 - Alerts you about o...
Little Snitch gives you control over your private outgoing data. Track background activity As soon as your computer connects to the Internet, applications often have permission to send any... Read more
OmniGraffle Pro 6.2.3 - Create diagrams,...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
OmniFocus 2.2 - GTD task manager with iO...
OmniFocus helps you manage your tasks the way that you want, freeing you to focus your attention on the things that matter to you most. Capturing tasks and ideas is always a keyboard shortcut away in... Read more
Cocktail 8.4 - General maintenance and o...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
PDFKey Pro 4.3 - Edit and print password...
PDFKey Pro can unlock PDF documents protected for printing and copying when you've forgotten your password. It can now also protect your PDF files with a password to prevent unauthorized access and/... Read more
Kodi 15.0.beta1 - Powerful media center...
Kodi (was XBMC) is an award-winning free and open-source (GPL) software media player and entertainment hub that can be installed on Linux, OS X, Windows, iOS, and Android, featuring a 10-foot user... Read more
DiskCatalogMaker 6.4.12 - Catalog your d...
DiskCatalogMaker is a simple disk management tool which catalogs disks. Simple, light-weight, and fast. Finder-like intuitive look and feel. Super-fast search algorithm. Can compress catalog data... Read more
Macs Fan Control 1.3.0.0 - Monitor and c...
Macs Fan Control allows you to monitor and control almost any aspect of your computer's fans, with support for controlling fan speed, temperature sensors pane, menu-bar icon, and autostart with... Read more
Lyn 1.5.11 - Lightweight image browser a...
Lyn is a lightweight and fast image browser and viewer designed for photographers, graphic artists and Web designers. Featuring an extremely versatile and aesthetically pleasing interface, it... Read more

Moleskine Timepage – Calendar for iCloud...
Moleskine Timepage – Calendar for iCloud, Google & Exchange 1.0 Device: iOS iPhone Category: Productivity Price: $4.99, Version: 1.0 (iTunes) Description: The most elegant calendar for your pocket and wrist, Timepage is a... | Read more »
QuizUp Gets Social in its New Update
Plain Vanilla Corp has released a new and improved version of their popular trivia game, QuizUp. The app now emphasizes social play so you can challenge friends from all over the world. [Read more] | Read more »
The Deep (Games)
The Deep 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Swipe Controls Delve into the deep in this retro rogue-like! Swipe to move your diver around and keep away from the enemies as you... | Read more »
Battle of Gods: Ascension (Games)
Battle of Gods: Ascension 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: TURN-BASED TACTICAL COMBATFight tactical battles against the forces of Hades! In Battle of Gods: Ascension you play... | Read more »
Shadowmatic's Latest Update Adds a...
Shadowmatic's shadowy shadow-ness is getting a little shadowy-er thanks to a recent update that adds an Arcade Mode. [Read more] | Read more »
Sunrise Calendar and Slack Have Assimila...
Wunderlist is perhaps one of the most populat and beloved productivity apps on the App Store - and now it's gone and incorporated itself into other useful services like Sunrise Calendar and Slack. [Read more] | Read more »
Crossy Road Devs Hipster Whale are Bring...
Hipster Whale, the minds behind the rather popular (and rather great) Crossy Road, have teamed-up with Bandai Namco to create PAC-MAN 256: an absolutely bonkers looking maze runner chaser thing. | Read more »
Meet the New Spotify Music
Spotify Music  has a lot going on. They're introducing 3 new modes to serve all your musical needs, with the "Now" start page  gives you curated playlists based on your particular tastes. As you listen the app will learn more about your tastes and... | Read more »
What the Apple Watch Gets Right, and Wha...
| Read more »
Celebrate PAC-MAN's 35th Birthday W...
BANDAI NAMCO Entertainment America is celebrating PAC-MAN's 35th anniversary by releasing updates for PAC-MAN and PAC-MAN Lite for iOS. [Read more] | Read more »

Price Scanner via MacPrices.net

What Would the ideal Apple Productivity Platf...
For the past four years I’ve kept a foot in both the Mac and iPad camps respectively. my daily computing hours divided about 50/50 between the two devices with remarkable consistency. However, there’... Read more
PageMeUp 1.2.1 Ten Dollar Page Layout Applica...
Paris, France-based Softobe, an OS X software development company, has announced that their PageMeUp v. 1.2.1, is available on the Mac App Store for $9.99. The license can be installed on up to 5... Read more
Eight New Products For USB Type-C Application...
Fresco Logic, specialists in advanced connectivity technologies and ICs, has introduced two new product families targeting the Type-C connector recently introduced across a number of consumer... Read more
Scripps National Spelling Bee Launches Buzzwo...
Scripps National Spelling Bee fans can monitor the action at the 2015 Spelling Bee with the new Buzzworthy app for iOS, Android and Windows mobile devices. The free Buzzworthy app provides friendly... Read more
13-inch 2.5GHz MacBook Pro on sale for $120 o...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $979 including free shipping plus NY sales tax only. Their price is $120 off MSRP, and it’s the lowest price for this model (except for Apple’... Read more
27-inch 3.3GHz 5K iMac on sale for $1899, $10...
B&H Photo has the new 27″ 3.3GHz 5K iMac on sale for $1899.99 including free shipping plus NY tax only. Their price is $100 off MSRP. Read more
Save up to $50 on iPad Air 2, NY tax only, fr...
B&H Photo has iPad Air 2s on sale for up to $50 off MSRP including free shipping plus NY sales tax only: - 16GB iPad Air 2 WiFi: $469 $30 off - 64GB iPad Air 2 WiFi: $549.99 $50 off - 128GB iPad... Read more
Updated Mac Price Trackers
We’ve updated our Mac Price Trackers with the latest information on prices, bundles, and availability on systems from Apple’s authorized internet/catalog resellers: - 15″ MacBook Pros - 13″ MacBook... Read more
New 13-inch 2.9GHz Retina MacBook Pro on sale...
B&H Photo has the 13″ 2.9GHz/512GB Retina MacBook Pro on sale for $1699.99 including free shipping plus NY tax only. Their price is $100 off MSRP, and it’s the lowest price for this model from... Read more
Apple refurbished 2014 MacBook Airs available...
The Apple Store has Apple Certified Refurbished 2014 MacBook Airs available starting at $679. An Apple one-year warranty is included with each MacBook, and shipping is free: - 11″ 1.4GHz/128GB... Read more

Jobs Board

Senior Software Engineer - *Apple* SIM - Ap...
Changing the world is all in a day039s work at Apple . If you love innovation, here039s your chance to make a career of it. You039ll work hard. But the job comes with Read more
Lead *Apple* Solutions Consultant - Retail...
**Job Summary** Job Summary The Lead ASC is an Apple employee who serves as the Apple business manager and influencer in a hyper-business critical Reseller's store Read more
Architect / Senior Software Engineer, *Apple...
Changing the world is all in a day039s work at Apple . If you love innovation, here039s your chance to make a career of it. You039ll work hard. But the job comes with Read more
*Apple* Pay Support Readiness Project Manage...
Changing the world is all in a day039s work at Apple . If you love innovation, here039s your chance to make a career of it. You039ll work hard. But the job comes with Read more
Hardware Design Validation Engineer - *Apple...
**Job Summary** The Apple Watch team is looking for a Hardware Design Validation Engineer. This person will be part of the Apple Watch hardware team with Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.