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







  
 
AAPL
$101.04
Apple Inc.
+0.51
MSFT
$45.02
Microsoft Corpora
-0.31
GOOG
$584.26
Google Inc.
-2.60

MacTech Search:
Community Search:

Software Updates via MacUpdate

Tidy Up 3.0.15.0 - Find duplicate files...
Tidy Up is a complete duplicate finder and disk-tidiness utility. With Tidy Up you can search for duplicate files and packages by the owner application, content, type, creator, extension, time... Read more
Parallels Desktop 10.0 - Run Windows app...
Parallels Desktop is simply the world's bestselling, top-rated, and most trusted solution for running Windows applications on your Mac. With Parallels Desktop for Mac, you can seamlessly run both... Read more
Apple Final Cut Pro X 10.1.3 - Professio...
Apple Final Cut Pro X is a professional video editing solution.Completely redesigned from the ground up, Final Cut Pro adds extraordinary speed, quality, and flexibility to every part of the post-... Read more
Apple Compressor 4.1.3 - Adds power and...
Compressor adds power and flexibility to Final Cut Pro X export. Customize output settings, work faster with distributed encoding, and tap into a comprehensive set of delivery features. Powerful... Read more
Chromium 36.0.1985.143 - Fast and stable...
Chromium is an open-source browser project that aims to build a safer, faster, and more stable way for all Internet users to experience the web. FreeSMUG-Free OpenSource Mac User Group build is... Read more
Macgo Blu-ray Player 2.10.6.1691 - Blu-r...
Macgo Mac Blu-ray Player can bring you the most unforgettable Blu-ray experience on your Mac. Overview Macgo Mac Blu-ray Player can satisfy just about every need you could possibly have in a Blu-ray... Read more
Apple Motion 5.1.2 - Create and customiz...
Apple Motion is designed for video editors, Motion 5 lets you customize Final Cut Pro titles, transitions, and effects. Or create your own dazzling animations in 2D or 3D space, with real-time... Read more
A Better Finder Rename 9.39 - File, phot...
A Better Finder Rename is the most complete renaming solution available on the market today. That's why, since 1996, tens of thousands of hobbyists, professionals and businesses depend on A Better... Read more
PopChar X 6.6 - Floating window shows av...
PopChar X helps you get the most out of your font collection. With its crystal-clear interface, PopChar X provides a frustration-free way to access any font's special characters. Expanded... Read more
MacUpdate Desktop 6.0.2 - Install Mac ap...
MacUpdate Desktop 6 brings seamless 1-click installs and version updates to your Mac. With a free MacUpdate account and MacUpdate Desktop 6, Mac users can now install almost any Mac app on macupdate.... Read more

Latest Forum Discussions

See All

Space Colors – Tips, Tricks, Strategies,...
Hello Cadets: Want to know what we thought about this hectic space combat/roguelike? Check out our Space Colors review! Space Colors is a cool shooter/roguelike from Team Chaos. You travel from planet to planet across a huge galaxy and complete a... | Read more »
Tap Sports Baseball – Tips, Tricks, and...
Tap Sports Baseball is a pretty simple game to learn, but that doesn’t mean it’s an easy game to master, by any means. To start your batting career off well, we thought we’d give you the heads up on some handy tips and tricks. Hey Batter-Batter:... | Read more »
Tap Sports Baseball Review
Tap Sports Baseball Review By Jennifer Allen on August 20th, 2014 Our Rating: :: LET'S PLAY BALLUniversal App - Designed for iPhone and iPad Tap Sports Baseball is briefly fun but lacks some important features.   | Read more »
Frontier Heroes Review
Frontier Heroes Review By Andrew Fisher on August 20th, 2014 Our Rating: :: BLAZES NO TRAILSUniversal App - Designed for iPhone and iPad Despite awesome visuals and great music, Frontier Heroes just doesn’t quite deliver enough fun... | Read more »
Echo Prime is Now on Sale for $0.99
Echo Prime is Now on Sale for $0.99 Posted by Jessica Fisher on August 20th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Star Realms Review
Star Realms Review By Andrew Fisher on August 20th, 2014 Our Rating: :: A STAR IS BORNUniversal App - Designed for iPhone and iPad Star Realms is an excellent adaptation of an outstanding deck-builder. With great visuals and an... | Read more »
This. Is. SPRINGFIELD! War comes to The...
This. Is. SPRINGFIELD! | Read more »
One Tap RPG Review
One Tap RPG Review By Campbell Bird on August 20th, 2014 Our Rating: :: DUNGEON SLIDERUniversal App - Designed for iPhone and iPad This casual arcade game introduces some very light rpg elements into its fantasy-themed pachinko... | Read more »
Goodbye Paywall – Table Tennis Touch Eli...
Goodbye Paywall – Table Tennis Touch Eliminates In-App Purchases Posted by Jessica Fisher on August 20th, 2014 [ permalink ] | Read more »
Go to Bed – An Interview With Touchfight...
Touchfight Games is an exciting new indie studio that was co-formed between game journalist and author Nathan Meunier, artist Leonard Kenyon, and programmer Jon Kenyon. Their debut game Go To Bed will be released this fall, and with all the... | Read more »

Price Scanner via MacPrices.net

Apple now offering certified refurbished 2014...
 The Apple Store is now offering Apple Certified Refurbished 2014 MacBook Airs for up to $180 off the cost of new models. An Apple one-year warranty is included with each MacBook, and shipping is... Read more
Best Buy’s College Student Deals: $100 off Ma...
Take an additional $100 off all MacBooks and iMacs, $50 off iPad Airs and iPad minis, at Best Buy Online with their College Students Deals Savings, valid through September 6th. Anyone with a valid .... Read more
MacBook Airs on sale for $100 off MSRP, free...
B&H Photo has three 2014 MacBook Airs on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only. They also include free copies of Parallels Desktop and LoJack for Laptops... Read more
Razer Taipan Mouse For Gamers And Non-Gamers...
If you’re a serious gamer on either Mac or Windows PCs, a serious gaming mouse is a necessity for first-tier performance. However, even if like me you’re not much of a gamer, there’s still a strong... Read more
15-inch 2.2GHz MacBook Pro on sale for $1899,...
Adorama has the new 15″ 2.2GHz Retina MacBook Pro on sale for $1899 including free shipping plus NY & NJ sales tax only. Their price is $100 off MSRP, and it’s the lowest price available for this... Read more
Mid-Size Tablet Shootout Posted: iPad mini wi...
I ‘m curious about how many iPads Apple is actually selling these days. It’s been widely rumored and anticipated that new models with A8 SoCs, 2 GB of RAM, 8 megapixel cameras, and fingerprint... Read more
The 15 Biggest iPad Air Problems And How To A...
What’s this? Fifteen “biggest” problems with the iPad Air? Does that mean there are a lot of smaller problems as well? Say it isn’t so! My old iPad 2 has manifested no hardware problems in three... Read more
TYLT Syncable-Duo, 2-in-1 USB Cable With Appl...
TYLT has introduced the Syncable-Duo, a universal cable solution for charging and syncing data to smartphones and tablets. The Syncable-Duo eliminates the need for multiple cables by incorporating... Read more
Save up to $140 off MSRP with Apple refurbish...
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
2.5GHz Mac mini on sale for $549, save $50
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

Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
*Apple* Solutions Consultant - Apple (United...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** Being a Business Manager at an Apple Store means you're the catalyst for businesses to discover and leverage the power, ease, and flexibility of Apple Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** At the Apple Store, you connect business professionals and entrepreneurs with the tools they need in order to put Apple solutions to work in their Read more
Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.