I have a plane defined by the standard plane equation a*x + b*y + c*z + d = 0, which I would like to be able to draw using OpenGL. How can I derive the four points needed to draw it as a quadrilateral in 3D space?
My plane type is defined as:
struct Plane {
float x,y,z; // plane normal
float d;
};
void DrawPlane(const Plane & p)
{
???
}
EDIT:
So, rethinking the question, what I actually wanted was to draw a discreet representation of a plane in 3D space, not an infinite plane. Base on the answer provided by @a.lasram, I have produced this implementation, which doest just that:
void DrawPlane(const Vector3 & center, const Vector3 & planeNormal, float planeScale, float normalVecScale, const fColorRGBA & planeColor, const fColorRGBA & normalVecColor)
{
Vector3 tangent, bitangent;
OrthogonalBasis(planeNormal, tangent, bitangent);
const Vector3 v1(center - (tangent * planeScale) - (bitangent * planeScale));
const Vector3 v2(center + (tangent * planeScale) - (bitangent * planeScale));
const Vector3 v3(center + (tangent * planeScale) + (bitangent * planeScale));
const Vector3 v4(center - (tangent * planeScale) + (bitangent * planeScale));
// Draw wireframe plane quadrilateral:
DrawLine(v1, v2, planeColor);
DrawLine(v2, v3, planeColor);
DrawLine(v3, v4, planeColor);
DrawLine(v4, v1, planeColor);
// And a line depicting the plane normal:
const Vector3 pvn(
(center[0] + planeNormal[0] * normalVecScale),
(center[1] + planeNormal[1] * normalVecScale),
(center[2] + planeNormal[2] * normalVecScale)
);
DrawLine(center, pvn, normalVecColor);
}
Where OrthogonalBasis() computes the tangent and bi-tangent from the plane normal.
To see the plane as if it's infinite you can find 4 quad vertices so that the clipped quad and the clipped infinite plane form the same polygon. Example:
Sample 2 random points P1
and P2
on the plane such as P1 != P2
.
Deduce a tangent t
and bi-tangent b
as
t = normalize(P2-P1); // get a normalized tangent
b = cross(t, n); // the bi-tangent is the cross product of the tangent and the normal
Compute the bounding sphere of the view frustum. The sphere would have a diameter D
(if this step seems difficult, just set D
to a large enough value such as the corresponding sphere encompasses the frustum).
Get the 4 quad vertices v1
, v2
, v3
and v4
(CCW or CW depending on the choice of P1 and P2):
v1 = P1 - t*D - b*D;
v2 = P1 + t*D - b*D;
v3 = P1 + t*D + b*D;
v4 = P1 - t*D + b*D;
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