# PixelSort

by James Hall: L6 Age ~16

## Introduction

James has produced a spectacular motion graphics application in only about a hundred lines of code. You can now try a web version. Click the left mouse button to create randomly coloured lines emanating from the cursor. Drag the mouse with the left button down to create effects similar to the example shown below. The path of each line depends upon the red, green and blue components of its colour.

Output

In order to run program PixelSort, you will need to have downloaded Stefan Berinde`s wingraph.zip file as described in our Graphics tutorial. You should copy the unzipped wincrt.pas, wingraph.pas and winmouse.pas (from the src folder) into your program folder. (The compiled units are included in the zip file but you might as well have the source code available for reference). You should find these three files useful for your own motion graphics programs.

## The Program

program PixelSort; { Copyright (c) 2011 James Hall Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License, as described at http://www.apache.org/licenses/ and http://www.pp4s.co.uk/licenses/ } uses SysUtils, wingraph, wincrt, winmouse, math; type Tpeeps = record x, y : array[1..200] of integer; colr, colg, colb : integer; realx, realy, targx, targy, speed, angle : real; end; var gd, gm : smallint; mousex, mousey, numpeeps, i, j, len : integer; screen : array[1..700,1..700] of integer; tehpeeps : array[1..10000] of Tpeeps; tri : array[1..3,1..3] of real; begin len := 2; numpeeps := 0; randomize; gd := 9; gm := 13; setwindowsize(700,700); initgraph(gd,gm,'PixelSort'); updategraph(updateoff); tri[1,1] := 0; tri[2,1] := 2*pi/3; tri[3,1] := 4*pi/3; repeat mousex := getmousex; mousey := getmousey; case getmousebuttons of MouseLeftButton : begin if numpeeps < 5000 then begin inc(numpeeps); with tehpeeps[numpeeps] do begin for i := 1 to len do begin x[i] := mousex; y[i] := mousey; end; realx := mousex; realy := mousey; colr := random(256); colg := random(256); colb := random(256); speed := 7; angle := 0; end; end; end; end; //case for i := 1 to 3 do begin tri[i,1] := tri[i,1] + pi/180; if tri[i,1] > 2*pi then tri[i,1] := tri[i,1] - 2 * pi; if tri[i,1] < 0 then tri[i,1] := tri[i,1] + 2 * pi; tri[i,2] := 350 + round(sin(tri[i,1])*200); tri[i,3] := 350 + round(cos(tri[i,1])*200); end; if numpeeps > 0 then for i := 1 to numpeeps do begin with tehpeeps[i] do begin angle := angle + pi/360; if colr+colb+colg <> 0 then begin targx := (colr*tri[1,2] + colg*tri[2,2] + colb * tri[3,2])/(colr+colb+colg); targy := (colr*tri[1,3] + colg*tri[2,3] + colb * tri[3,3])/(colr+colb+colg); end; if (targy-realy) < 0 then angle := arctan((targx-realx)/(targy-realy)) + pi; if (targy-realy) > 0 then angle := arctan((targx-realx)/(targy-realy)); if ((targy-realy) = 0) then if (targx-realx) > 0 then angle := pi/2 else angle := 3*pi/2; if angle > 2*pi then angle := angle - 2*pi; if angle < 0 then angle := angle + 2*pi; realx := realx + sin(angle)*speed; realy := realy + cos(angle)*speed; for j := 1 to len-1 do begin x[len+1-j] := x[len-j]; y[len+1-j] := y[len-j]; end; x[1] := round(realx); y[1] := round(realy); for j := 1 to len-1 do begin setcolor(colr+256*colg+65536*colb); line(x[j],y[j],x[j+1], y[j+1]); end; end; end; updategraph(updatenow); until closegraphrequest; end.

We intend to replace this code with a commented version using meaningful variable names.

## Remarks

Can you think of a program like this that you could write?