* * * * *
                                        
                    All that for something barely anyone saw
                                        
One of the problems of providing an RSS feed (Really Simple Syndication) [1]
is that most of my readers read it and not the site here, thus the format
change I did for April 1^st was lost, along with most of my AdSense [2]
revenue (one of the few things I can report about is my gross earnings from
Google [3], which to the nearest cent is $0.00)—I suppose I may get more
revenue if I inline the ads, such as:

 

But I don't really want to do that (nor add ads to my RSS (Really Simple
Syndication) feed, so don't worry—well, except possibly for this entry but
that depends on if your RSS agregator filters out the <SCRIPT> tag (it'll be
interesting to see).

Anyway … 

Last year's April Fools theme was greenbar printer paper, where (through the
wonders of CSS (Cascading Style Sheets)) it appeared as if this was being
printed out (in all caps no less) and it took me quite a while to find an
appropriate image of greenbar paper for the background. This years idea was
to do an old fasion monochrome monitor (green on black) with a slight resync
problem (you can see a bright green line of the electron gun being swept
across the screen). A bit easier to munge up than last year's imagry and one
I could make myself.

At first I tried a paint program, but it was a rather primitive paint program
and I had problems trying to do the 2048x100 image (2048 pixels wide to make
sure it was wide enough not to repeat for anyone). Too many problems using
the program, leading it to taking way too long.

It was then I remembered I had the GD library [4] installed.

Trivial!

How trivial?

> #include <stdio.h>
> #include <stdlib.h>
> #include "gd.h"
> 
> int main(void)
> {
>   FILE       *fpout;
>   gdImagePtr  imout;
>   int         background;
>   int         line[3];
> 
>   imout = gdImageCreate(2048,100);
> 
>   background = gdImageColorAllocate(imout,16, 32,16);
>   line[0]    = gdImageColorAllocate(imout,16, 64,16);
>   line[1]    = gdImageColorAllocate(imout,16, 96,16);
>   line[2]    = gdImageColorAllocate(imout,16,128,16);
> 
>   gdImageLine(imout,0,13,2047,23,line[0]);
>   gdImageLine(imout,0,14,2047,24,line[1]);
>   gdImageLine(imout,0,15,2047,25,line[2]);
>   gdImageLine(imout,0,16,2047,26,line[1]);
>   gdImageLine(imout,0,17,2047,27,line[0]);
> 
>   fpout = fopen("vidline.png","wb");
>   gdImagePng(imout,fpout);
>   fclose(fpout);
>   gdImageDestroy(imout);
>   return(EXIT_SUCCESS);
> }
> 

A crude attempt at anti-aliasing a beam across the page. Very poor results no
matter how I did it. It was then I remembered my Foley-van Dam book
(_Computer Graphics: Principles and Practice_ [5] by Foley, van Dam, Feiner
and Hughes, 2^nd Edition)—surely it must have a section on anti-aliasing
lines. Indeed, § 3.17 had just what I wanted—code for drawing anti-aliased
lines. A few minutes typing in the code (a page's worth) and I had myself one
nice anti-aliased beam across the page.

> int g_brightness[100];
> 
> /********************/
> 
> void init_colors(gdImagePtr img)
> {
>   int i;
>   
>   for (i = 0 ; i < 100 ; i++)
>     g_brightness[i] = gdImageColorAllocate(img,16,132-i,16);
> }
> 
> /******************/
> 
> void pset(gdImagePtr img,int x,int y,double dist)
> {
>   int    intensity;
>   
>   intensity = (int)(fabs(dist) / 1.5 * 100.0);
>   gdImageSetPixel(img,x,y,g_brightness[intensity]);
> }
> 
> /***********************/
> 
> void line(gdImagePtr img,int x1,int y1,int x2,int y2)
> {
>   int    dx;
>   int    dy;
>   int    incrE;
>   int    incrNE;
>   int    d;
>   int    x;
>   int    y;
>   int    two_v_dx;
>   double invDenom;
>   double two_dx_invDenom;
>   
>   dx              = x2 - x1;
>   dy              = y2 - y1;
>   d               = 2 * dy - dx;
>   incrE           = 2 * dy;
>   incrNE          = 2 * (dy - dx);
>   two_v_dx        = 0;		
>   invDenom        = 1.0 / (2.0 * sqrt(dx*dx + dy+dy));
>   two_dx_invDenom = 2.0 * (double)dx * invDenom;
>   x               = x1;
>   y               = y1;
>   
>   pset(img,x,y    ,0.0);
>   pset(img,x,y + 1,two_dx_invDenom);
>   pset(img,x,y - 1,two_dx_invDenom);
>   
>   while(x < x2)
>   {
>     if (d < 0)
>     {
>       two_v_dx = d + dx;
>       d += incrE;
>       x++;
>     }
>     else
>     {
>       two_v_dx = d - dx;
>       d += incrNE;
>       x++;
>       y++;
>     }
>   
>     pset(img,x,y    ,two_v_dx * invDenom);
>     pset(img,x,y + 1,two_dx_invDenom - two_v_dx * invDenom);
>     pset(img,x,y - 1,two_dx_invDenom + two_v_dx * invDenom);
>   }
> }
> 

See what I go through for stuff nobody will see?

Sigh.

(If you are curious to see the styles, and you are using Firefox [6], you can
use the menu View/Page Style to select which style you want).

[1] https://boston.conman.org/bostondiaries.rss
[2] http://www.google.com/ads/
[3] http://www.google.com/
[4] http://www.boutell.com/gd/
[5] http://www.amazon.com/exec/obidos/ASIN/0201848406/conmanlaborat-20
[6] http://www.mozilla.org/products/firefox/central.html

Email Sean Conner at sean@conman.org

.