pjdixit

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About pjdixit

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  1. [quote name='Burnt_Fyr' timestamp='1351627382' post='4995551'] for an example in code, look for Eberle's paper on clipping a mesh against a plane. It has a function Get ordered vertices that does exactly what you want, and describes the process, which is essentially the same as Khos described. Pixalot's method will work as well, but might be confusing in the realm of 3d, where left and right are not absolutes. [/quote] After googling a little bit more I found it. Here is the link in case someone else needs it : http://www.geometrictools.com/Documentation/ClipMesh.pdf. I will go through it and will get back if it solves the problem. Thank you!!
  2. Hi..thanks you everyone for getting back. Can you please send me a link to Eberle's paper you mentioned?
  3. I really need some urgent help with this problem. I have a set of edges and vertices defining a polygon (not necessarily convex). The vertices and edges are in random order and I want to sort/order the vertices of this polygon in clockwise (or anti-clock wise) direction. please see this page for more detailed description: http://www.dixittech.com/blog/2012/10/28/sorting-vertices-of-a-polygon-in-ccw-or-cw-direction/ Any idea how this can be achieved?
  4. If I know field of view angle and current view volume co-ordinates defined by left_perspective, right_perspective, top_perspective, bottom_perspective, zNear, zFar. Then is it possible to some how find equivalent view volume in orthographic mode, that is left_ortho, right_ortho, top_ortho, bottom_ortho, zNear, zFar? Is it possible to reverse it (to get perspective view volume if I know orthographic view volume and FOV angle?)
  5. [quote name='pjdixit' timestamp='1334692819' post='4932264'] How did I miss that! That should work... [/quote] I guess i spoke too early. Even with correct normals because of zero-area triangles there is flickering of edges and there are artifacts with stencil shadows. I suppose it is because of limited precision of depth buffer.
  6. [quote name='irreversible' timestamp='1334690991' post='4932243'] As a robust workaround, why do you need to recalculate the normal for each triangle? You already know it per face - why can't you use that? [/quote] How did I miss that! That should work... I guess it wasn't very obvious to me as per vertex normals were re-calculated for each triangle based on the geometry and connectivity information for smooth shading in a separate dll. I guess I just need to figure out a way to pass normal information to the dll and to block re-calculation of normal for zero-area triangles. Thanks a lot!
  7. [b] [url="http://www.dixittech.com/blog/2012/04/16/glutesselator-issues-with-zero-area-triangles-and-t-intersections/"]GLUtesselator : Issues with zero-area triangles and T-intersections[/url][/b] [font=inherit][color=#373737][font=inherit][size=4]I came across this issue when I was trying to triangulate Text entities using GLUtesselator. However, it can occur during triangulation of any polygon using GLUtesselator. The problem is that sometimes GLUtesselator generates zero-area triangles. Most of the times you can ignore them but there are cases where they can’t be ignored. I am trying to find a solution so that final triangulation of a given polygon do not have any zero-area triangles or T-intersections. As far as I know, GLUtesselator is one of the most robust and stable tesselator available so I would like to stick to it and won’t mind doing some post-processing to fix the triangulation rather than writing a new tesselator myself.[/size][/font][/color][/font] [color=#373737][size=4] [font=inherit]I will try to demonstrate the problem with tessellation of character ‘H’. Input vertices to the GLUtesselator are:[/font] [/size][/color] [center][url="http://www.dixittech.com/blog/wp-content/uploads/2012/04/H_input.jpg"][img]http://www.dixittech.com/blog/wp-content/uploads/2012/04/H_input.jpg[/img][/url][/center] [font=inherit][font=inherit]This is how it was triangulated using GLUtesselator. I set the winding to GLU_TESS_WINDING_ODD and GLU_TESS_TOLERANCE was set to default 0.[/font][/font] [center][font=inherit][url="http://www.dixittech.com/blog/wp-content/uploads/2012/04/H_Tesselation4.jpg"][img]http://www.dixittech.com/blog/wp-content/uploads/2012/04/H_Tesselation4.jpg[/img][/url][/font][/center] [center] [font=inherit][url="http://www.dixittech.com/blog/wp-content/uploads/2012/04/vertexlist-table3.jpg"][img]http://www.dixittech.com/blog/wp-content/uploads/2012/04/vertexlist-table3.jpg[/img][/url][/font] [font=inherit]After preliminary inspection of the triangulation, it seemed as if there were T-intersections at vertex 5 and 10 which raised a red flag as the geometry was further processed by half-edge data structure and T-intersections were not allowed.[/font] [/center] [center][font=inherit][url="http://www.dixittech.com/blog/wp-content/uploads/2012/04/H_T-Intersection2.jpg"][img]http://www.dixittech.com/blog/wp-content/uploads/2012/04/H_T-Intersection2.jpg[/img][/url][/font][/center] [font=inherit]However, generating the list of triangles showed that tessellation actually generated zero-area triangles and not T-intersections. Here is the list of generated triangles:[/font] [center][font=inherit][url="http://www.dixittech.com/blog/wp-content/uploads/2012/04/table_trilist2.jpg"][img]http://www.dixittech.com/blog/wp-content/uploads/2012/04/table_trilist2.jpg[/img][/url][/font][/center] [center][font=inherit][b]Legend : T = True , F = False[/b][/font][/center] [font=inherit]The problem is that I can’t use zero-area triangles either as I can’t calculate normal or equation of plane correctly for zero-area triangles. Normals and equation of planes can be very critical for implementing smoothing and shadow generation algorithms so they need to have a valid value.[/font] [font=inherit]So, I am stuck here with a very bad situation: If I have zero-area triangles then I can’t calculate normal and equation of plane correctly which is a must. It is trivial to remove zero-area triangles but if I remove them then I am stuck with T-intersections and I can’t live with them either.[/font] [font=inherit]So I would like to make sure that in cases where GLUtesselator generates zero-area triangles, my application will re-triangulate a sub-portion of the polygon such that there are no zero-area triangles or T-intersections. For our example case, triangulation should look some thing like this:[/font] [center][font=inherit][url="http://www.dixittech.com/blog/wp-content/uploads/2012/04/H_Wanted_Tesselation1.jpg"][img]http://www.dixittech.com/blog/wp-content/uploads/2012/04/H_Wanted_Tesselation1.jpg[/img][/url][/font][/center] [font=inherit]I think its a very fundamental problem and a solution to it will benefit lot of developers working in a similar area. I am sure I am not the first one to stumble upon it. Any suggestions how it can be done? Any alternate approach is very welcome as well.[/font]