nehe: add nehe opengl example

examples/nehe/nehe2.factor

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+IN: nehe
+USING: kernel gadgets opengl math arrays ;
+
+TUPLE: nehe2-gadget ;
+
+: width 256 ;
+: height 256 ;
+
+C: nehe2-gadget (  -- gadget )
+  [ delegate>gadget ] keep ;
+
+M: nehe2-gadget pref-dim* ( gadget -- dim )
+  drop width height 0 3array ;
+
+: gl-begin ( type quot -- )
+  >r glBegin r> call glEnd ; inline
+
+M: nehe2-gadget draw-gadget* ( gadget -- )
+  drop
+  GL_PROJECTION glMatrixMode
+  glLoadIdentity
+  45.0 width height / >float 0.1 100.0 gluPerspective
+  GL_MODELVIEW glMatrixMode
+  glLoadIdentity
+  GL_SMOOTH glShadeModel
+  0.0 0.0 0.0 0.0 glClearColor
+  1.0 glClearDepth
+  GL_DEPTH_TEST glEnable
+  GL_LEQUAL glDepthFunc
+  GL_PERSPECTIVE_CORRECTION_HINT GL_NICEST glHint
+  GL_COLOR_BUFFER_BIT GL_DEPTH_BUFFER_BIT bitor glClear
+  glLoadIdentity
+  -1.5 0.0 -6.0 glTranslatef
+  GL_TRIANGLES [
+    0.0 1.0 0.0 glVertex3f
+    -1.0 -1.0 0.0 glVertex3f
+    1.0 -1.0 0.0 glVertex3f
+  ] gl-begin
+  3.0 0.0 0.0 glTranslatef
+  GL_QUADS [
+    -1.0 1.0 0.0 glVertex3f
+    1.0 1.0 0.0 glVertex3f
+    1.0 -1.0 0.0 glVertex3f
+    -1.0 -1.0 0.0 glVertex3f
+  ] gl-begin ;
+
+: run ( -- )
+  <nehe2-gadget> "NeHe Tutorial 2" open-titled-window ;