GLScene MeshObjects
lazarus / 70-OpenGL

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dicepd · 2017-08-22 11:26

Have got around to the next stage of my program where I need
parametric mesh generation for both display and calculation.

Borrowing from Jeromes code which he has offered at various times
(GLMeshObjectHelper) I started off easy just trying to create a two
tri plane (GLMeshObjectHelper uses quads, I need tris for computation
reasons). All kind of works with the exception of the displayed faces.

This is the basic code for generating the plane:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TTestMeshObject.MakePlane(width, depth: Single);var  X, Y:
Single;begin  X := width / 2.0;  Y := depth / 2.0;   // define a rect
coplanar to the xy plane  // raised by 12 units in the positive Z
axis   // define vertices in CCW rotation from xy positive quadrant 
AddNormal(0, 0, 1);    // normal is positive z for all vertices 
AddTexCoords(0, 1);  AddVertex(X, Y, 12);   AddNormal(0, 0, 1); 
AddTexCoords(1, 1);  AddVertex(X, -Y, 12);   AddNormal(0, 0, 1); 
AddTexCoords(0, 1);  AddVertex(-X, -Y, 12);   AddNormal(0, 0, 1); 
AddTexCoords(1, 0);  AddVertex(-X, Y, 12);   // Define two tris from a
viewpoint looking towards neg Z  // i.e standard top viewpoint in a
real world orientation  AddFace(0,1,2);  // top right, top left,
bottom left     CCW winding  AddFace(0,2,3);  // top right, bottom
left, bottom right  CCW winding   // This should result in a rect
which is 12 units above the xy plane  // back culled faces should be
the faces facing the origin. end;  
However GLScene backculls the top of the plane and not the bottom.
I can't change the winding order of the tris as that is the expected
winding for computation routines.

So something is wrong. Possibilties:


I have done something wrong in the generation code and can no longer
see the wood from the trees.
I am missing some setting or not calling some base class method which
should be called.
I found a bug.


Attached is a working test project which fully demonstrates the issue.

Peter

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dicepd · 2017-08-22 12:52

Looks like my own stupidity

Points 2 and 4 transposed.

Ah well writing about it cleared the head.

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BeanzMaster · 2017-08-27 08:07

Hi, good   Don't remember if i don't answer here don't forget to post
questions on : https://sourceforge.net/p/glscene/discussion/

Just a question the procedure MakePlane in my unit "GLMeshObjectHelpe"
don't work correctly ? What is her last modified date ? because i
posted severals version in GLScene's forum.

Cheers