62 lines
2.6 KiB
C#
62 lines
2.6 KiB
C#
using OpenTK.Mathematics;
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namespace VoxelEngine.Rendering;
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// View-frustum for culling chunk AABBs. Built from a world→clip matrix in this
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// engine's row-vector convention (clip = worldPos * view * projection, matching
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// the chunk vertex shader). Planes point inward; a point is inside when it is on
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// the positive side of all six.
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public readonly struct Frustum
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{
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// Each Vector4 is (a, b, c, d) for plane a*x + b*y + c*z + d = 0, normalized.
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private readonly Vector4 _left, _right, _bottom, _top, _near, _far;
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private Frustum(Vector4 l, Vector4 r, Vector4 b, Vector4 t, Vector4 n, Vector4 f)
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{
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this._left = l; this._right = r; this._bottom = b;
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this._top = t; this._near = n; this._far = f;
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}
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// `vp` maps a world-space row vector p to clip space via p * vp. In that
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// convention clip.x = p · column0, clip.w = p · column3, etc., so each plane
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// is a combination of vp's columns (Gribb–Hartmann, row-vector form).
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public static Frustum FromViewProjection(Matrix4 vp)
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{
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Vector4 c0 = vp.Column0, c1 = vp.Column1, c2 = vp.Column2, c3 = vp.Column3;
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return new Frustum(
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Normalize(c3 + c0), // left: clip.w + clip.x >= 0
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Normalize(c3 - c0), // right: clip.w - clip.x >= 0
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Normalize(c3 + c1), // bottom: clip.w + clip.y >= 0
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Normalize(c3 - c1), // top: clip.w - clip.y >= 0
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Normalize(c3 + c2), // near: clip.w + clip.z >= 0 (GL NDC z in [-1,1])
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Normalize(c3 - c2)); // far: clip.w - clip.z >= 0
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}
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// True if the axis-aligned box [min,max] is at least partially inside.
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public bool Intersects(Vector3 min, Vector3 max)
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{
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return InsideOrCrossing(this._left, min, max)
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&& InsideOrCrossing(this._right, min, max)
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&& InsideOrCrossing(this._bottom, min, max)
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&& InsideOrCrossing(this._top, min, max)
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&& InsideOrCrossing(this._near, min, max)
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&& InsideOrCrossing(this._far, min, max);
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}
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// The box is fully outside a plane only if its most-positive vertex (the
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// corner farthest along the plane normal) is still behind the plane.
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private static bool InsideOrCrossing(Vector4 plane, Vector3 min, Vector3 max)
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{
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float px = plane.X >= 0 ? max.X : min.X;
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float py = plane.Y >= 0 ? max.Y : min.Y;
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float pz = plane.Z >= 0 ? max.Z : min.Z;
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return plane.X * px + plane.Y * py + plane.Z * pz + plane.W >= 0f;
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}
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private static Vector4 Normalize(Vector4 p)
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{
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float len = new Vector3(p.X, p.Y, p.Z).Length;
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return len > 0f ? p / len : p;
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}
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}
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