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  1. #1
    Regular Contributor
    Join Date
    Jan 2005
    Posts
    154

    Draw two faces of a Polygon in OpenGL ES!!

    Hello,

    i have just found out that glPolygonMode() function is not implemented in OGLES?!!! How can i draw the two faces of a polygon without this function?

    cheers
    AF

  2. #2
    Regular Contributor
    Join Date
    Apr 2007
    Location
    Germany, Stuttgart
    Posts
    241

    Re: Draw two faces of a Polygon in OpenGL ES!!

    I'm not sure if I got your question right. glPolygonMode is to select a mode how a polygon is painted ( GL_POINT, GL_LINE, GL_FILL ), and to select on which faces this mode is used.
    Both faces will be painted, if you deactivate cull face with glDisable(GL_CULL_FACE). To select only one face to be drawn activate cull face and use glCullFace(GL_BACK) or GL_FRONT.
    The drawing mode (points, line, triangles) can be selected directly in the glDrawArrays( GL_LINES,.... ) statements.

    I hope this was helpfull...

    Best Regards,
    Andi

  3. #3
    Nokia Developer Expert
    Join Date
    Mar 2003
    Posts
    68

    Re: Draw two faces of a Polygon in OpenGL ES!!

    Hi.

    glPolygonMode() is actually NOT part of the OpenGL ES API. As only *triangles* are supported as a way to render polygons, there is no need for this API entry point. LINEs and POINTs are supported as render primitives (but not as polygon render modes).

    If the original question was about two-sided lighting (since OpenGL ES does not support separate materials for front and back), then there is no other way than to render two-sided geometry twice (once with front material and once with back material and setting cullface/frontface accordingly).

    glCullFace() and glFrontFace() are supported normally.

    Jani Vaarala
    Graphics Architect
    Nokia

  4. #4
    Regular Contributor
    Join Date
    Jan 2005
    Posts
    154

    Re: Draw two faces of a Polygon in OpenGL ES!!

    Thanx for the reply.
    Actually i was confused a bit with glPolygonMode and its GL_FILL mode. I did not think about the GL_CULL_FACE state!! Now i got both faces rendered fully.

    cheers

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