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

Audio Hijack 3.2.0 - Record and enhance...
Audio Hijack (was Audio Hijack Pro) drastically changes the way you use audio on your computer, giving you the freedom to listen to audio when you want and how you want. Record and enhance any audio... Read more
FontExplorer X Pro 5.0.1 - Font manageme...
FontExplorer X Pro is optimized for professional use; it's the solution that gives you the power you need to manage all your fonts. Now you can more easily manage, activate and organize your... Read more
Calcbot 1.0.2 - Intelligent calculator a...
Calcbot is an intelligent calculator and unit converter for the rest of us. Featuring an easy-to-read history tape, expression view, intuitive conversion, and much more! Features History Tape -... Read more
MTR 5.0.0.1 - The Mac's oldest and...
MTR (was MacTheRipper)--the Mac's oldest and smartest DVD-backup app--is now updated to version 5.001 MTR -- the complete toolbox, not a one-trick, point-and-click extractor. MTR is intended for... Read more
LibreOffice 4.4.5.2 - Free, open-source...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
Adobe Lightroom 6.1.1 - Import, develop,...
Adobe Lightroom is available as part of Adobe Creative Cloud for as little as $9.99/month bundled with Photoshop CC as part of the photography package. Lightroom 6 is also available for purchase as a... Read more
File Juicer 4.41 - Extract images, video...
File Juicer is a drag-and-drop can opener and data archaeologist. Its specialty is to find and extract images, video, audio, or text from files which are hard to open in other ways. It finds and... Read more
A Better Finder Rename 9.52 - 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
OmniFocus 2.2.3 - GTD task manager with...
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
TinkerTool 5.4 - Expanded preference set...
TinkerTool is an application that gives you access to additional preference settings Apple has built into Mac OS X. This allows to activate hidden features in the operating system and in some of the... Read more

Cosmonautica (Games)
Cosmonautica 1.1 Device: iOS Universal Category: Games Price: $6.99, Version: 1.1 (iTunes) Description: Cast off! Are you ready for some hilarious adventures in outer space? | Read more »
Rescue humanity from a Demon horde in An...
Angel Stone is Fincon's follow up to the massively successful Hello Hero and is out now on iOS and Android. You play as a member of The Resistance, a group of mighty human warriors who have risen up in defiance of the Demon horde threatening to... | Read more »
Gallery Doctor (Photography)
Gallery Doctor 1.0 Device: iOS iPhone Category: Photography Price: $2.99, Version: 1.0 (iTunes) Description: Free up valuable iCloud and iPhone storage with Gallery Doctor, the only iPhone cleaner that automatically identifies the... | Read more »
You Against Me (Games)
You Against Me 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: A simple game… You. Me. Claim, steal, lock, score, win! | Read more »
Yep, it's True - Angry Birds 2 is O...
The not exactly rumors were true and the birds are back. Angry Birds 2 has come to the App Store and the world will... well I suppose it'll still be the same, but now we have more bird-flinging options! [Read more] | Read more »
You Could Design Your Own Card for Chain...
If you've ever wanted to create your own item, weapon, trap, or even monster for Chainsaw Warrior: Lords of the Night, this is your chance. Auroch Digital is currently holding a contest so that fans can fight to the death (not really) to see which... | Read more »
Bitcoin Billionaire is Going Back in Tim...
If you thought you managed to buy everything there is to buy in Bitcoin Billionaire and make all the money, well you though wrong. Those of you who made it far enough might remember investing in time travel - and it looks like that investment is... | Read more »
Domino Drop (Games)
Domino Drop 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Domino Drop is a delightful new puzzle game with dominos and gravity!Learn how to play it in a minute, master it day by day.Your... | Read more »
OPERATION DRACULA (Games)
OPERATION DRACULA 1.0.1 Device: iOS Universal Category: Games Price: $5.99, Version: 1.0.1 (iTunes) Description: 25% off launch sale!!! 'Could prove to be one of the most accurate representations of the Japanese bullet hell shmup... | Read more »
Race The Sun (Games)
Race The Sun 1.01 Device: iOS iPhone Category: Games Price: $4.99, Version: 1.01 (iTunes) Description: You are a solar craft. The sun is your death timer. Hurtle towards the sunset at breakneck speed in a futile race against time.... | Read more »

Price Scanner via MacPrices.net

Sale! 13-inch MacBook Pros on sale for $100 o...
B&H Photo has 13″ MacBook Pros on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.5GHz/500GB MacBook Pro: $999.99 save $100 - 13″ 2.7GHz/128GB Retina... Read more
Sale! Save $100 on 13-inch MacBook Airs this...
B&H Photo has the 13″ 1.6GHz/128GB MacBook Air on sale for $899.99 including free shipping plus NY tax only. Their price is $100 off MSRP, and it’s the lowest price available for this model.... Read more
Worldwide Tablet Market Decline Continues, Ap...
The worldwide tablet market declined -7.0% year-over-year in the second quarter of 2015 (2Q15) with shipments totaling 44.7 million units according to preliminary data from the International Data... Read more
TP-LINK TL-PA8030P KIT Powerline Featuring Ho...
Consumer and business networking products provider TP-LINK is now shipping its TL-PA8030P KIT AV1200 3-Port Gigabit Passthrough Powerline Starter Kit that expands your home’s network over its... Read more
Apple refurbished iPad Air 2s available for u...
The Apple Store has Apple Certified Refurbished iPad Air 2s available for up to $140 off the price of new models. Apple’s one-year warranty is included with each model, and shipping is free: - 128GB... Read more
Updated Apple iPad Price Trackers
We’ve updated our iPad Air Price Tracker and our iPad mini Price Tracker with the latest information on prices and availability from Apple and other resellers. Read more
Apple refurbished 2014 13-inch 128GB MacBook...
The Apple Store has Apple Certified Refurbished 2014 13″ MacBook Airs available starting at $759. An Apple one-year warranty is included with each MacBook, and shipping is free: - 13″ 1.4GHz/128GB... Read more
Apple’s Education discount saves up to $300 o...
Purchase a new Mac or iPad at The Apple Store for Education and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free,... Read more
Save up to $600 with Apple refurbished Mac Pr...
The Apple Store has Apple Certified Refurbished Mac Pros available for up to $600 off the cost of new models. An Apple one-year warranty is included with each Mac Pro, and shipping is free. The... Read more
Mac Pros on sale for up to $260 off MSRP
B&H Photo has Mac Pros on sale for up to $260 off MSRP. Shipping is free, and B&H charges sales tax in NY only: - 3.7GHz 4-core Mac Pro: $2799, $200 off MSRP - 3.5GHz 6-core Mac Pro: $3719.99... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
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* Online Store UAT Lead - Apple (Unite...
**Job Summary** The Apple Online Store is a fast paced and ever evolving business environment. The User Acceptance Testing (UAT) lead in this organization is able to Read more
*Apple* MAC Support Services Subject Matter...
Title: Apple MAC Support Services Subject Matter Expert Location: Pleasanton, CA Type of position: Temporary Contract for approximately 6 weeks Tasks The tasks for the Read more
Lead Infrastructure Engineer - *Apple* /Mac P...
…of a team * Requires proven problem solving skills Preferred Additional: * Apple Certified System Administrator (ACSA) * Apple Certified Technical Coordinator (ACTC) Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.