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
$101.58
Apple Inc.
+0.72
MSFT
$46.52
Microsoft Corpora
-0.24
GOOG
$584.77
Google Inc.
+4.82

MacTech Search:
Community Search:

Software Updates via MacUpdate

iExplorer 3.5.0.0 - View and transfer al...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more
BusyCal 2.6 - Powerful calendar app with...
BusyCal is an award-winning desktop calendar that combines personal productivity features for individuals with powerful calendar sharing capabilities for families and workgroups. BusyCal's unique... Read more
Apple iOS 8.0 - The latest version of Ap...
The latest version of iOS can be downloaded through iTunes. Apple iOS 8 comes with big updates to apps you use every day, like Messages and Photos. A whole new way to share content with your family.... Read more
Apple Digital Camera RAW Compatibility 5...
Apple Digital Camera RAW Compatibility update adds RAW image compatibility to Aperture 3 and iPhoto '11. For more information on supported RAW formats, see here.Version 5.07: Adds RAW camera... Read more
Transmit 4.4.7 - Excellent FTP/SFTP clie...
Transmit is an excellent FTP (file transfer protocol), SFTP, S3 (Amazon.com file hosting) and iDisk/WebDAV client that allows you to upload, download, and delete files over the internet. With the... Read more
Macgo Blu-ray Player 2.10.8.1715 - 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
Capture One Pro 8.0.0.433 - RAW workflow...
Capture One Pro 8 is a professional RAW converter offering you ultimate image quality with accurate colors and incredible detail from more than 300 high-end cameras -- straight out of the box. It... Read more
Adobe Acrobat Pro 11.0.09 - Powerful PDF...
Adobe Acrobat allows users to communicate and collaborate more effectively and securely. Unify a wide range of content in a single organized PDF Portfolio. Collaborate through electronic document... Read more
Adobe Reader 11.0.09 - View PDF document...
Adobe Reader allows users to view PDF documents. You may not know what a PDF file is, but you've probably come across one at some point. PDF files are used by companies and even the IRS to... Read more
iFFmpeg 4.6.1 - Convert multimedia files...
iFFmpeg is a graphical front-end for FFmpeg, a command-line tool used to convert multimedia files between formats. The command line instructions can be very hard to master/understand, so iFFmpeg does... Read more

Latest Forum Discussions

See All

KuaiBoard (formerly QuickBoard) (Utilit...
KuaiBoard (formerly QuickBoard) 1.0 Device: iOS Universal Category: Utilities Price: $1.99, Version: 1.0 (iTunes) Description: KuaiBoard is currently 50% off for launch! Billing info. Signatures. Locations. KuaiBoard allows you to... | Read more »
Treasure Fetch - Adventure Time (Games)
Treasure Fetch - Adventure Time 1.0.1 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.1 (iTunes) Description: Adventure Time Treasure Fetch is a fresh take on the classic Snake game! STRETCHY JAKE Snake your way... | Read more »
Light in the Dark (Games)
Light in the Dark 1.1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.1.0 (iTunes) Description: Be enlightened by this delightful puzzle game that has never before seen the light of day! "A physics and color-blending... | Read more »
Transmit iOS (Utilities)
Transmit iOS 1.0 Device: iOS Universal Category: Utilities Price: $9.99, Version: 1.0 (iTunes) Description: >> LAUNCH SPECIAL: Transmit iOS is ONLY $10 for a LIMITED TIME. << THE #1 FILE TRANSFER CLIENT FOR THE MAC NOW... | Read more »
Minuum - The Little Keyboard for Big Fin...
Minuum - The Little Keyboard for Big Fingers 1.0 Device: iOS iPhone Category: Utilities Price: $1.99, Version: 1.0 (iTunes) Description: Type faster, see more of your screen, and take control of autocorrect with Minuum: the little... | Read more »
TextExpander 3 + custom keyboard (Utili...
TextExpander 3 + custom keyboard 3.0 Device: iOS Universal Category: Utilities Price: $4.99, Version: 3.0 (iTunes) Description: | Read more »
Swype - Keyboard (Utilities)
Swype - Keyboard 1.0.1411 Device: iOS Universal Category: Utilities Price: $.99, Version: 1.0.1411 (iTunes) Description: Why type when you can Swype? One of the most requested apps for iPhone is finally here. "If Swype itself ever... | Read more »
Joinz (Games)
Joinz 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Joinz is a clever block sliding puzzle game that is easy to play, nice to look at but tricky to master. You will be coming back again... | Read more »
Little World Escape Review
Little World Escape Review By Jordan Minor on September 17th, 2014 Our Rating: :: EARTHBOUNDUniversal App - Designed for iPhone and iPad Little World Escape draws players in with captivating concepts before pushing them away with... | Read more »
Light in the Dark Review
Light in the Dark Review By Nadia Oxford on September 17th, 2014 Our Rating: :: LIGHT 'EM UP UP UPUniversal App - Designed for iPhone and iPad Light in the Dark is an interesting and challenging puzzle game with some amusing bits... | Read more »

Price Scanner via MacPrices.net

Logitech Bluetooth Multi-Device Cross-Platfor...
Logitech has an enviable track record of making some of the best computer keyboards and mice. At least in my estimation, the best freestanding keyboards I’ve ever used have been Logitech units,... Read more
Roundup of Apple refurbished iPad Airs and iP...
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
Sprint offers 16GB iPad mini for $199.99 with...
Sprint is offering 1st generation 16GB iPad minis for $199.99 with a 2-year service agreement. Standard MSRP for this iPad is $429. Their price is the lowest available for this model. Read more
2.5GHz Mac mini remains on sale for $549, sav...
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
Apple refurbished iMacs available for up to $...
The Apple Store has Apple Certified Refurbished iMacs available for up to $300 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free. These are the best prices on... Read more
13″ 2.5GHz MacBook Pro offered for $100 off M...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $999.99 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more
Free GIMP Professional Grade Graphics App Ver...
The latest 2.8.14 version of the oddly-named GIMP (acronym for: GNU Image Manipulation Program) open source, high-end image editing and creation alternative to Adobe’s Photoshop and refuge from... Read more
Apple Announces Record Pre-orders for iPhone...
Apple has released metrics showing a record number of first day pre-orders of iPhone 6 and iPhone 6 Plus, with over four million sold in the first 24 hours. Demand for the new iPhones exceeds the... Read more
10% off iPhone 6 and 6 Plus Otterbox cases
Get 10% off on popular Otterbox iPhone 6 and iPhone 6 Plus cases at MacMall through September 19th. Use code OTTERBOX10 to see the discount. Read more
15-inch MacBook Pros on sale for up to $125 o...
Amazon has the new 2014 15″ Retina MacBook Pros on sale for up to $125 off MSRP including free shipping: - 15″ 2.2GHz Retina MacBook Pro: $1899.99 save $100 - 15″ 2.5GHz Retina MacBook Pro: $2374... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.