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Orange
9212b1f51f
Adds comprehensive documentation for the pattern scanning API. Details parsing behavior, complexity, and usage examples. Includes troubleshooting tips and minimal test sketches. Clarifies edge-case handling and implementation notes.
99 lines
2.9 KiB
Markdown
99 lines
2.9 KiB
Markdown
# `omath::primitives::create_plane` — Build an oriented quad (2 triangles)
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> Header: your project’s `primitives/plane.hpp`
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> Namespace: `omath::primitives`
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> Depends on: `omath::Triangle<omath::Vector3<float>>`, `omath::Vector3<float>`
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```cpp
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[[nodiscard]]
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std::array<Triangle<Vector3<float>>, 2>
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create_plane(const Vector3<float>& vertex_a,
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const Vector3<float>& vertex_b,
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const Vector3<float>& direction,
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float size) noexcept;
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```
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---
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## What it does
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Creates a **rectangle (quad)** in 3D oriented by the edge **A→B** and a second in-plane **direction**. The quad is returned as **two triangles** suitable for rendering or collision.
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* Edge axis: `e = vertex_b - vertex_a`
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* Width axis: “direction”, **projected to be perpendicular to `e`** so the quad is planar and well-formed.
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* Normal (by right-hand rule): `n ∝ e × width`.
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> **Sizing convention**
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> Typical construction uses **half-width = `size`** along the (normalized, orthogonalized) *direction*, i.e. the total width is `2*size`.
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> If your implementation interprets `size` as full width, adjust your expectations accordingly.
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---
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## Parameters
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* `vertex_a`, `vertex_b` — two adjacent quad vertices defining the **long edge** of the plane.
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* `direction` — a vector indicating the **cross-edge direction** within the plane (does not need to be orthogonal or normalized).
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* `size` — **half-width** of the quad along the (processed) `direction`.
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---
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## Return
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`std::array<Triangle<Vector3<float>>, 2>` — the quad triangulated (consistent CCW winding, outward normal per `e × width`).
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---
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## Robust construction (expected math)
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1. `e = vertex_b - vertex_a`
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2. Make `d` perpendicular to `e`:
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```
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d = direction - e * (e.dot(direction) / e.length_sqr());
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if (d.length_sqr() == 0) pick an arbitrary perpendicular to e
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d = d.normalized();
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```
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3. Offsets: `w = d * size`
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4. Four corners:
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```
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A0 = vertex_a - w; A1 = vertex_a + w;
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B0 = vertex_b - w; B1 = vertex_b + w;
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```
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5. Triangles (CCW when viewed from +normal):
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```
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T0 = Triangle{ A0, A1, B1 }
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T1 = Triangle{ A0, B1, B0 }
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```
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---
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## Example
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```cpp
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using omath::Vector3;
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using omath::Triangle;
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using omath::primitives::create_plane;
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Vector3<float> a{ -1, 0, -1 }; // edge start
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Vector3<float> b{ 1, 0, -1 }; // edge end
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Vector3<float> dir{ 0, 0, 1 }; // cross-edge direction within the plane (roughly +Z)
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float half_width = 2.0f;
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auto quad = create_plane(a, b, dir, half_width);
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// e.g., compute normals
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for (const auto& tri : quad) {
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auto n = tri.calculate_normal(); (void)n;
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}
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```
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---
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## Notes & edge cases
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* **Degenerate edge**: if `vertex_a == vertex_b`, the plane is undefined.
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* **Collinearity**: if `direction` is parallel to `vertex_b - vertex_a`, the function must choose an alternate perpendicular; expect a fallback.
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* **Winding**: If your renderer expects a specific face order, verify and swap the two vertices in each triangle as needed.
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