doc-en/par-eclairageponctuel-en.tex

   1 \newpage
   2 \section{Lighting by a point light source}
   3
   4 Two parameters, the first one positions the \Index{light source}, the second one sets the \Index{light intensity}:
   5 \begin{compactitem}
   6     \item \Lkeyword{lightsrc}=20 30 50 in Cartesian coordinates, or
   7 \texttt{\Lkeyword{lightsrc}=\Lkeyval{viewpoint}} to put the light source at the view point.
   8     \item \texttt{\Lkeyword{lightintensity}=2} (default value).
   9 \end{compactitem}
  10 \begin{center}
  11 \newcommand\LIGHTSRC[3]{%
  12 \pstVerb{
  13          /xLIGHTSRC #1 def
  14          /yLIGHTSRC #2 def
  15          /zLIGHTSRC #3 def
  16          /RADIUS 4 def
  17          /THETA yLIGHTSRC xLIGHTSRC atan def
  18          /DISTANCE xLIGHTSRC dup mul  yLIGHTSRC dup mul add zLIGHTSRC dup mul add sqrt def
  19          /PHI zLIGHTSRC DISTANCE div arcsin def
  20          /ALPHA RADIUS DISTANCE div arccos def
  21          /OH ALPHA cos RADIUS mul def
  22          /radius_cone ALPHA sin RADIUS mul def
  23          /Hauteur_cone DISTANCE OH sub def
  24          /X_C xLIGHTSRC OH mul DISTANCE div def
  25          /Y_C yLIGHTSRC OH mul DISTANCE div def
  26          /Z_C zLIGHTSRC OH mul DISTANCE div def
  27          /rotX_axe_cone PHI 90 sub def
  28          /rotZ_axe_cone THETA 90 sub def
  29          }
  30 \psset{Decran=50,viewpoint=50 10 15}
  31 \psSolid[object=sphere,r=RADIUS,fillcolor=blue,ngrid=18 36,
  32         lightsrc=xLIGHTSRC yLIGHTSRC zLIGHTSRC](0,0,0)
  33 \psPoint(xLIGHTSRC,yLIGHTSRC,zLIGHTSRC){LS}
  34 \psset{lightsrc=}
  35 \psSolid[object=cone,r=radius_cone,h=Hauteur_cone,fillcolor=yellow!50,
  36        ngrid=1 36,RotX=rotX_axe_cone,RotZ=rotZ_axe_cone,opacity=0.5,
  37        linecolor=yellow](X_C,Y_C,Z_C)
  38 \psdot(LS)}
  39
  40 \begin{pspicture}(-2,-2.5)(5,5)
  41 \psset{unit=0.5}
  42 \LIGHTSRC{0}{8}{8}
  43 \uput[45](LS){Light Source}
  44 \axesIIID(4,4,4)(6,6,6)
  45 \end{pspicture}
  46 \begin{pspicture}(-4,-2.5)(5,2.5)
  47 \psset{unit=0.5}
  48 \LIGHTSRC{2}{-5}{0}
  49 \uput[l](LS){Light Source}
  50 \axesIIID(4,4,4)(6,6,6)
  51 \end{pspicture}
  52
  53 \begin{pspicture}(-1,-2.5)(9,2.5)
  54 \psset{unit=0.5}
  55 \LIGHTSRC{0}{20}{0}
  56 \uput[r](LS){Light Source}
  57 \axesIIID(4,4,4)(6,6,6)
  58 \end{pspicture}
  59 \end{center}
  60
  61 As you can see, the intersecting \Index{plane} (section of the sphere with the cone of
  62 \Index{light}) divides the object into two half spaces: the first half space
  63 (the one on the side of the \Index{light source}) is illuminated and the other half space is the shadow region referring to this light source position.
  64
  65 Now it is clear, that if the view point is setup with the same coordiates as the light source, the object is illuminated uniquely.
  66
  67 \encadre{In order to get some shadow regions to appear in the graphic---which emphasises the 3D character---we would suggest choosing the light source and the view point differently.}
  68
  69 \newpage
  70 Here follow a few examples:
  71
  72 \begin{pspicture}(-3,-2)(3,3)
  73 \psset{unit=0.3}
  74 \psset{Decran=1e3,
  75     viewpoint=500 0 1000,
  76     lightsrc=10 20 30,mode=3}
  77 \psSolid[object=sphere,r=5,fillcolor=blue](0,0,8)
  78 \rput(0,-3.5){\texttt{lightsrc=10 20 30}}
  79 \end{pspicture}
  80 \begin{pspicture}(-3,-2)(3,3)
  81 \psset{unit=0.3}
  82 \psset{Decran=1e3,
  83     viewpoint=500 0 1000,
  84     lightsrc=-10 -20 30,mode=3}
  85 \psSolid[object=sphere,r=5,fillcolor=blue](0,0,8)
  86 \rput(0,-3.5){\texttt{lightsrc=-10 -20 30}}
  87 \end{pspicture}
  88 \begin{pspicture}(-3,-2)(3,3)
  89 \psset{unit=0.3}
  90 \psset{Decran=1e3,
  91     viewpoint=500 0 1000,
  92     lightsrc=30 -20 30,mode=3}
  93 \psSolid[object=sphere,r=5,fillcolor=blue](0,0,8)
  94 \rput(0,-3.5){\texttt{lightsrc=30 -20 30}}
  95 \end{pspicture}
  96
  97 When the option \verb+[lightsrc=value1 value2 value3]+
  98 is not specified, the object is uniformly illuminated.
  99
 100 \begin{center}
 101  \begin{pspicture}(-6,-2)(6,2)
 102 %\psframe(-6,-4)(6,4)
 103 \psset{viewpoint=50 50 30 rtp2xyz,Decran=40,unit=0.6}
 104 \psSolid[object=datfile,file=./tore1836,deactivatecolor]
 105  %\psSolid[r1=3.5,r0=1,object=tore,ngrid=18 36,fillcolor={[rgb]{.372 .62 .628}}]%
 106  \axesIIID(0,4.5,0)(6,6,4)
 107  \end{pspicture}
 108 \end{center}
 109
 110
 111
 112 Here are some examples, where we always keep the same object, the same view point, the same light
 113 source coordinates and just vary the \Lkeyword{lightintensity} value:
 114
 115 \begin{pspicture}(-3,-2)(3,3)
 116 \psset{unit=0.3}
 117 \psset{Decran=1e3,
 118     viewpoint=500 0 1000,
 119     lightsrc=-10 -20 30,mode=4,lightintensity=1}
 120 \psSolid[object=sphere,r=5,fillcolor=green](0,0,8)
 121 \rput(0,-3.5){\texttt{lightintensity=2}}
 122 \end{pspicture}
 123 \begin{pspicture}(-3,-2)(3,3)
 124 \psset{unit=0.3}
 125 \psset{Decran=1e3,
 126     viewpoint=500 0 1000,
 127     lightsrc=-10 -20 30,mode=4,lightintensity=3}
 128 \psSolid[object=sphere,r=5,fillcolor=green](0,0,8)
 129 \rput(0,-3.5){\texttt{lightintensity=3}}
 130 \end{pspicture}
 131 \begin{pspicture}(-3,-2)(3,3)
 132 \psset{unit=0.3}
 133 \psset{Decran=1e3,
 134     viewpoint=500 0 1000,
 135     lightsrc=-10 -20 30,mode=4,lightintensity=8}
 136 \psSolid[object=sphere,r=5,fillcolor=green](0,0,8)
 137 \rput(0,-3.5){\texttt{lightintensity=8}}
 138 \end{pspicture}
 139
 140 Here we can see, that by increasing the \Lkeyword{lightintensity} value, the shading nuances of the solid are decreasing.
 141
 142
 143
 144 \endinput