frustum() - question about the definition of coordinates of clipping planes

edited November 2017 in Programming Questions

Hello Community,

can somebody explain to me how to define the coordinates of the clipping planes of a viewing frustum? I cannot find a clear answer on the processing page.

As it is only one coordinate per plane i can imagine it to be a kind of offset. Maybe the coordinate for the left clipping plane is the offset from the left side of the near-plane to the left side of the far-plane?

Thank you for your help!



  • it's just the value of y, isn't it? if you have a left clipping plane at -10 then anything with a y less than that gets clipped.

    the big question is whether that's transformed coordinates or not.

    (a hint might be to look at the opengl frustum documentation because the processing version is generally a thin layer on top of the opengl original)

  • Extract from OpenGL Red Book

    Screen Shot 2017-11-30 at 10.50.15

    void glFrustum(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble near, GLdouble far);

    Creates a matrix for a perspective-view frustum and multiplies the current matrix by it. The frustum's viewing volume is defined by the parameters: (left, bottom, -near) and (right, top, -near) specify the (x, y, z) coordinates of the lower-left and upper-right corners of the near clipping plane; near and far give the distances from the viewpoint to the near and far clipping planes. They should always be positive. The frustum has a default orientation in three-dimensional space. You can perform rotations or translations on the projection matrix to alter this orientation, but this is tricky and nearly always avoidable.

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