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13640 :: How to convert/cast seq[GLfloat_t] to openArray[Vertex] were Vertex = GLfloat[0..2]

• hmf (orginal) [2026-01-08T15:58:42+01:00] view original

  Hello,

  I am trying to cast a seq[GLfloat_t] to an openArray[Vertex] where:

  
  type
    Vertex* = object
      x*, y*, z*: GLfloat_t
  Run

  I have tried the following but these do not compile:

  
    let vp: seq[Vertex] = ...
    let t1 = cast[openArray[Vertex]](vp.addr)
    let t2 = cast[openArray[Vertex]](addr(vp[0]))
    let t3 = cast[openArray[GLfloat_t]](addr(vp[0]))
  Run

  The following works for ptr Vertex:

  
    var t0  = cast[ptr Vertex](vp.addr)
    var t1  = cast[ptr Vertex](addr(vp[0]))
  Run

  But I cannot seem t use these as arguments to:

  
  proc vertices_vbo(vertices: openArray[Vertex]): GLuint_t = ...
  Run

  What am I missing here?

  TIA

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• hmf (orginal) [2026-01-08T17:09:52+01:00] view original

  Go it to compile with:

  
    let vpv = cast[ptr UncheckedArray[Vertex]](vp[0].addr)
    doAssert vp.len mod 3 == 0
    let points_vbo = vertices_vbo(vpv.toOpenArray(0, vp.len div 3 - 1))
    let vao: GLuint_t = vao_of(points_vbo)
  Run

  My search also led me to a use:

  
  type
    Vertex* {.bycopy, packed.} = object
      x*, y*, z*: GLfloat_t
  
  static:
    assert sizeof(Vertex) == 3 * sizeof(GLfloat_t)
  Run

  Seems to be working. I just don't know if that .bcopy. is critical, but seeing as I am using a C API, I think it is best to use it.

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