symdat <'vertexData' is a pointer to the data (not header).
If you want to update without re-assigning the name, you
could do something like
p=. symdat <'vertexData'
d=. 1&fc (new vertex data)
d memw p,0,(#d),2
but beware of any side effects
Tue, 03 Mar 2020, Brian Schott написал(а):
> All,
>
> Recall that I am (re)developing a multiple turtle, turtle graphics system
> using modern openGL. I have been unable to find examples of how to do this,
> and the examples that come close use C++ and GLM which hide from me some of
> the essentials. What follows is my current understanding of how I might
> proceed. I want advice, please.
>
> Consider the "model-view" line (just below) for transformations in
> shader.ijs. (The "Projection" line immediately after the "model-view" line
> in the code is not relevant to my comments.)
>
> NB. model-view (*********line wrap is bad here********)
> mvp=: (gl_Rotate (0{R), 1 0 0 ) mp (gl_Rotate (1{R), 0 1 0) mp (gl_Rotate
> (2{R), 0 0 1) mp (gl_Scale STEPS%100) mp (gl_Translate 0 0 _8) mp
> glu_LookAt EYE,LR,UD,IO,UP
>
> But I do not think that "model-view" line can be used effectively in a
> turtleS (plural) graphical system because the calculation is really moving
> the system camera (I call it the Eye) so it can focus on a specific target
> in the scene.
>
> I believe, but want to proved wrong, that instead each turtle has to have
> its own vertexData array and that array must be rewritten after each
> position or heading change. It is possible that only turtles that do so
> move require a change of their vertices and position. Furthermore, a
> separate current heading matrix and gl_Position for each turtle must be
> computed and stored after each rotation and translation, respectively.
>
> I may be wrong about gl_Position above, because that special value may be
> associated with the camera and not with the individual objects. Does anyone
> know about that?
>
> If I am correct that each turtle's moving or turning vertices have to be
> altered, I believe I understand how gl_Rotate and gl_Translate can be
> applied to vertices to generate knew vertices, and how a new 3x3 heading
> array can be computed after each rotation and how revised position vectors
> can be computed. Saving the heading array and the position vectors may be
> more efficient in j than in openGL, but I have not thought that through.
>
> It seems to me that it might be very desirable to save the revised
> vertexData vertices in their original location so that the pointer in
> "symdat <'vertexData'" can be used without rebinding the vector buffer. But
> I have no idea if or how that might be done. Help, please.
>
> Any help on these issues would be greatly appreciated.
>
> --
> (B=)
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
--
regards,
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