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Thread: Plot 3D : both solid fill and wireframe triangles

  1. #1
    Junior Member Newbie
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    Plot 3D : both solid fill and wireframe triangles

    Hi

    I'm a newbie in OpenGL. I'm trying to create a C# library to plot (X,Y,Z) surface made from connected triangles (I just pass axis X and Y array.

    My specs are:

    * each triangle just use a plain color depending on their z-value (gradient: red to blue) => no lighting / shade effect.

    * the resulting surface is "solid" (filled) along with its wireframe (in black).

    * labeling (text and decimal) on axes shall be displayed.

    Questions:

    * Do you know any existing open-source implementation for .NET ?

    * Do you recommand to use GL_TRIANGLE_STRIP or GL_TRIANGLES to build the surface ?

    * How to both fill a triangle AND draw its black border ? I couldn't find any satisafctory answer...


    Best Regards,

  2. #2
    Advanced Member Frequent Contributor
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    Re: Plot 3D : both solid fill and wireframe triangles

    1. i know that there are, but i haven't used C# myself, take a look at nehe.gamedev.net, i know that there are some C# openGL examples there.

    2. GL_TRIANGLES is definitely easier to use than GL_TRIANGLE_STRIP.

    3. simple first draw them as solids, then draw them as wireframe, perhaps with some polygon offset if needed.

  3. #3
    Junior Member Newbie
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    Re: Plot 3D : both solid fill and wireframe triangles

    thanks zeoverlord


    I'll give a try to the polygon offset because drawing polygon fill+line does not look professional at all.

    I actually find another thread talkingabout this :

    http://www.opengl.org/discussion_boa...=020246#000000

    but obviously there are still limitations ... so NO definitive solution to this ???

    :°(

  4. #4
    Super Moderator OpenGL Lord
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    Re: Plot 3D : both solid fill and wireframe triangles

    Values 1.0 1.0 seem to be good for a lot of cases.

  5. #5
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    Re: Plot 3D : both solid fill and wireframe triangles

    Well thanks!

    The use of glPolygonOffset(1,1) seems satisfactory at this time.

    zeoverlord says that GL_TRIANGLES is definitely easier to use than GL_TRIANGLE_STRIP. Ok but what about performance in my case (solid fill + wireframe) : will it improve ?

  6. #6
    Super Moderator OpenGL Lord
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    Re: Plot 3D : both solid fill and wireframe triangles

    Triangle strips can be a bit better for perf, and well suited for regular grids.
    For arbitrary triangles, stay with GL_TRIANGLES for a start.

    Do you have performance problems now ?
    Try display lists, or VBO.

  7. #7
    Senior Member OpenGL Pro
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    Re: Plot 3D : both solid fill and wireframe triangles

    For using C# with OpenGL, you should have a look at the Tao framework. It comes with tons of examples, including a C# implementation of the NeHe tutorials.

    EDIT: Forgot the link
    http://www.taoframework.com/

  8. #8
    Junior Member Newbie
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    Re: Plot 3D : both solid fill and wireframe triangles

    Ok thanks for the answers.

    I'll take a look at Tao : does it provide code example of efficent 3d plotting (solid fill + wireframe) ?

    I got another problem : coloring the triangles. I choose to paint them each with a uniform color depending on their z-value. From blue to red - how surprising ;-)
    My solution is based on a color gradient : for that the code uses the HSL color space to move the hue according to the z-value (float between 0-red and 0.666-blue). What I don't understand is that if I lower the saturation and brightness, the plot becomes completely *white* !!??!

    Is that linked to the color depth associated with my opengl scene ? Am I in 256 colors only ? How can I check and how to change it ??? (I couldn't figure that out)


    Best regards

  9. #9
    Super Moderator OpenGL Lord
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    Re: Plot 3D : both solid fill and wireframe triangles

    >>the code uses the HSL color space to move the hue according to the z-value
    Most likely you have a bug in this part of the code.

  10. #10
    Junior Member Newbie
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    Re: Plot 3D : both solid fill and wireframe triangles

    ok,

    I guess by default opengl windows lib works at 24 or 32 bits color depth ?

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