minigl | A minimal Game Library built on top of the Gosu gem | Game Engine library

You have to use glVertexAttribIPointer, when defining the array of generic vertex attribute data, for the vertex attrbute in ivec3 Glob_pos;. glVertexAttribPointer is for floating point attributes only (integral data will be converted to floating point).

See the Khronos group reference page for glVertexAttribPointer:

For glVertexAttribPointer, if normalized is set to GL_TRUE, it indicates that values stored in an integer format are to be mapped to the range [-1,1] (for signed values) or [0,1] (for unsigned values) when they are accessed and converted to floating point. Otherwise, values will be converted to floats directly without normalization.

For glVertexAttribIPointer, only the integer types GL_BYTE, GL_UNSIGNED_BYTE, GL_SHORT, GL_UNSIGNED_SHORT, GL_INT, GL_UNSIGNED_INT are accepted. Values are always left as integer values.

Note, probably Glob_pos is never set and has always the same, but undefined value.

Since you don't use glGetAttribLocation to get the attribute indices for the vertex attributes (position, color, Glob_pos), you should use Layout Qualifiers: