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	demo.design 3D programming FAQ

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ÎÑÂÅÙÅÍÈÅ<br>5.1. Ìîäåëü îñâåùåíèÿ

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<p>Îñâåùåííîñòü ïðîèçâîëüíî âçÿòîé òî÷êè P, ïîÿâèâøóþñÿ èç-çà èñòî÷íèêà ñâåòà,
èçëó÷àþùåãî âî âñå ñòîðîíû (omnilight) â îáùåì ñëó÷àå áóäåì âû÷èñëÿòü ïî
óðàâíåíèþ Ôîíãà:

<p class=expression>ambient = Ka,<br>
diffuse = Kd * cos(N, L),<br>
specular = Ks * pow(cos(R, V), Ns),<br>
intensity = ambient + amp * (diffuse + specular).<br>

<p><center><img src="illu/illu51a.gif" width=270 height=180 alt="ðèñóíîê (illu/illu51a.gif)"></center>

<p>Çäåñü èñïîëüçîâàíû ñëåäóþùèå îáîçíà÷åíèÿ:

<p><table width=480 cellspacing=0 cellpadding=0 border=0 align=center>
<tr><td valign=top><p class=expression>Ka</div></td><td>êîýôôèöèåíò ôîíîâîé èíòåíñèâíîñòè (õàðàêòåðèñòèêà îêðóæàþùåé ñðåäû)</td></tr>
<tr><td><p class=expression>Kd</td><td>êîýôôèöèåíò ðàññåÿíèÿ (õàðàêòåðèñòèêà ïîâåðõíîñòè)</td></tr>
<tr><td><p class=expression>Ks</td><td>êîýôôèöèåíò îòðàæåíèÿ (õàðàêòåðèñòèêà ïîâåðõíîñòè)</td></tr>
<tr><td><p class=expression>Ns</td><td>êîýôôèöèåíò âèäà îòðàæåíèÿ (õàðàêòåðèñòèêà ïîâåðõíîñòè)</td></tr>
<tr><td><p class=expression>amp</td><td>"ìîùíîñòü" èñòî÷íèêà ñâåòà</td></tr>
<tr><td><p class=expression>P</td><td>ðàññìàòðèâàåìàÿ òî÷êà</td></tr>
<tr><td><p class=expression>N</td><td>íîðìàëü ê ïîâåðõíîñòè èçîáðàæàåìîãî îáúåêòà â òî÷êå P</td></tr>
<tr><td><p class=expression>L</td><td>âåêòîð, ïðîâåäåííûé èç òî÷êè P â èñòî÷íèêà ñâåòà (ëó÷ ñâåòà)</td></tr>
<tr><td><p class=expression>V</td><td>âåêòîð, ïðîâåäåííûé èç òî÷êè P â "òî÷êó çðåíèÿ" êàìåðû</td></tr>
<tr><td><p class=expression>R</td><td>îòðàæåííûé ëó÷ ñâåòà (îòðàæåíèå L îòíîñèòåëüíî N)</td></tr>
<tr><td><p class=expression>ambient</td><td>"ôîíîâàÿ" îñâåùåííîñòü</td></tr>
<tr><td><p class=expression>diffuse</td><td>"ðàññåÿííàÿ" îñâåùåííîñòü</td></tr>
<tr><td><p class=expression>specular</td><td>"îòðàæåííàÿ" îñâåùåííîñòü</td></tr>
<tr><td><p class=expression>intensity</td><td>îñâåùåííîñòü (ñóììàðíàÿ)</td></tr>
<tr><td><p class=expression>cos(A,B)</td><td>êîñèíóñ óãëà ìåæäó âåêòîðàìè A è B</td></tr>
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<p>Ýòî óðàâíåíèå äàæå ïîääàåòñÿ îòíîñèòåëüíî ïðîñòîìó îáúÿñíåíèþ - îñâåùåííîñòü
êàê áû ñêëàäûâàåòñÿ èç ôîíîâîãî óðîâíÿ îñâåùåííîñòè, ðàññåÿííîãî (ïî âñåì
íàïðàâëåíèÿì - à çíà÷èò, è ïî íàïðàâëåíèþ ãëàçà) â ýòîé òî÷êå ñâåòà îò
èñòî÷íèêà è îòðàæåííîãî (òîæå â ãëàç) ñâåòà îò èñòî÷íèêà.

<p>Êàê îáû÷íî, ðàñ÷åòû ïî ýòîé ôîðìóëå äàäóò äîâîëüíî ðåàëèñòè÷íûé ðåçóëüòàò,
íî ñ÷èòàòü âñå ýòî äëÿ êàæäîé òî÷êè ãðàíè ñëèøêîì ìåäëåííî.

<p>Äà, êîñèíóñ óãëà ìåæäó âåêòîðàìè ñ÷èòàåòñÿ êàê

<p class=expression>cos(A,B) = A*B/(|A|*|B|),<br>

<p>ãäå A*B - ñêàëÿðíîå ïðîèçâåäåíèå âåêòîðîâ, |A| è |B| - èõ äëèíû. Ïîýòîìó
èìååò ñìûñë âñå âåêòîðû ïåðåä èñïîëüçîâàíèåì ïðèâåñòè ê äëèíå 1, òîãäà
êîñèíóñ óãëà ìåæäó âåêòîðàìè áóäåò ðàâåí èõ ñêàëÿðíîìó ïðîèçâåäåíèþ.
Íåáîëüøàÿ îïòèìèçàöèÿ.

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