Here's a version that has the correct appearence.
However, it does it at the expense of repeating
the edges of the quads, so each normal applies to
each set of separately added four vertices, which is
not good either.
Another idea is that probably the normal should be
calculated by the edge and not by the face, since in
the unadulterated quad strip each face is added only
with another edge. The value of the edge normal would
be the average of the two adjacent face normals.
Does that make sense?
NB. =========================================================
gsngon=: 3 : '+. (_1^2%y)*^:(<y) 1'
P=: gsngon 4 NB. regular planar polygon
P0=: P,._1
P1=: P,. 1
Q=: _3]\,P0,.P1 NB. quad strip (last not added to look inside)
GS_AMBIENT=: 0.15
GS_DIFFUSE=: 0.7
GS_SPECULAR=: 0.7
GS_ROTXYZ=: 294 360 287
paint=: 3 : 0
gsinit GS_LIGHT
gsdrawviewbox RED
(0.05;YELLOW) gsmark 4{. Q
(0.05;CYAN ) gsmark 2{.4}.Q
gsdrawpolygon P0;(gsnormal P0);RED
gsdrawpolygon P1;(gsnormal P1);BLUE
gsdrawquadstrip Q;'';GREEN
gsfini''
)
NB. ------------------------- TBD in jzopenglutil.ijs ---
gsnormal=: (% +/&.(*:"_))@(+/)
gsvertnorm=: glVertex [ [EMAIL PROTECTED]
gsquadnorms=: (2,:4)&(gsvertnorm;._3)
gsdrawquadstrip=: 3 : 0 "2
'v n c'=. y
v=. gscol3 v
if. #c do. gscolor c end.
glBegin GL_QUAD_STRIP
gsquadnorms v
glEnd''
)
gsmark=: 0.1&$: : (4 : 0)"1
glPushMatrix ''
glTranslate y
gsdrawcube&>/ 2{.(boxopen x),<SKYBLUE
glPopMatrix ''
)
----- Original Message ----
From: Brian Schott <[EMAIL PROTECTED]>
To: Programming forum <[email protected]>
Sent: Saturday, July 29, 2006 12:05:37 PM
Subject: Re: [Jprogramming] opengl geometry meshes?
Oleg,
I altered your script to show the flat sides more
clearly. I added the following line to your paint verb
below gsinit.
glShadeModel GL_FLAT
This resulted in more distinct sides, but may not have been
what you wanted. I think you can see the result by holding
down the right-arrow or up-arrow key and watching the
lighting change. I see the most dramatic changes with the
right- or left-arrow key movements from the original
position.
I noticed a peculiar feature in the graphic that may
be a reult of your model, or may be a "feature" of the J
openGL. The feature is that the light shading changes
dramatically as soon as you press any scene movement key,
such as j, x, or arrow. Whereas initially the forward end of
the cylinder is brightly lit, as soon as any key is pressed
(while the graphic window is in focus), the same end is NOT
lit any longer.
Btw, I ran your graphic by embedding it in the file
/Users/brian/j601/system/examples/graphics/opengl/demo/glviews.ijs
. This is done by replacing the 2 characters "XX" in the
file by your code.
(B=)
On Thu, 27 Jul 2006, Oleg Kobchenko wrote:
+ Well, I don't see how OpenGL automatically creates
+ normals. In all examples with light and n-gons (strips, quads, etc.)
+ the normals are explicit. Thus, we can have the utility
+ verb to optionally automatically generate the normals,
+ as shown below. Though I don't like the result very much:
+ there's definitely some normals, but are they correct?
+
+ P=: +. (4%:_1)*^:(<8) 1 NB. regular planar octagon
+ P0=: P,._1
+ P1=: P,. 1
+ Q=: _3]\,P0,.P1 NB. quad strip (last not added to look inside)
+
+ GS_AMBIENT=: 0.15
+ GS_DIFFUSE=: 0.7
+ GS_SPECULAR=: 0.7
+ GS_ROTXYZ=: 25 40 0
+
+ paint=: 3 : 0
+ gsinit GS_LIGHT
+ gsdrawviewbox RED
+ gsdrawpolygon P0;'';RED
+ gsdrawpolygon P1;'';BLUE
+ gsdrawquadstrip Q;'';GREEN
+ gsfini''
+ )
+
+ NB. ========================= TBD in jzopenglutil.ijs ===
+ gsnormal=: (% +/&.(*:"_))@(+/)
+ gsquadnormal=: (2,:4)&(gsnormal;._3)
+
+ gsdrawquadstrip=: 3 : 0 "2
+ 'v n c'=. y
+ v=. gscol3 v
+ if. 0=#n do. n=. gsquadnormal v end.
+ if. #c do. gscolor c end.
+ glBegin GL_QUAD_STRIP
+ for_i. i.&.-: #v do.
+ if. i>0 do. glNormal (-:i-2){n end.
+ glVertex (i+i.2){v
+ end.
+ glEnd''
+ )
+
+
+ ----- Original Message ----
+ From: "Miller, Raul D" <[EMAIL PROTECTED]>
+ To: Programming forum <[email protected]>
+ Sent: Thursday, July 27, 2006 8:08:39 PM
+ Subject: RE: [Jprogramming] opengl geometry meshes?
+
+
+ Oleg Kobchenko wrote:
+ > Here's the simplest I could think of.
+ > But no triangles here: a polygon and a quad strip.
+
+ Thanks.
+
+ I'll try to look at it in more depth when I have the
+ chance to figure out jzopenglutil.
+
+ > The problem here is light/normals: it looks like
+ > OpenGL cannot automatically figure out normals (?).
+
+ That's odd. Normally it does.
+
+ And they're extremely simple to figure out --
+ take the (3d) cross product of the two vectors
+ leading out from any corner of a face, and the
+ result is normal to that face. Divide by the
+ length and you have the normal.
+
+ I was under the impression that opengl did
+ this by default unless you configured it
+ such that you're providing normals manually.
+
+ --
+ Raul
+
+ ----------------------------------------------------------------------
+ For information about J forums see http://www.jsoftware.com/forums.htm
+ ----------------------------------------------------------------------
+ For information about J forums see http://www.jsoftware.com/forums.htm
+
(B=) <----------my "sig"
Brian Schott
Atlanta, GA, USA
schott DOT bee are eye eh en AT gee em ae eye el DOT com
http://schott.selfip.net/~brian/
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
