subdivision.hh

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/*
 
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Copyright (c) 2026 PCSX-Redux authors
 
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*/
 
#pragma once
 
#include <stdint.h>
 
#include "psyqo/primitives/common.hh"
#include "psyqo/vector.hh"
 
namespace psyqo {
 
namespace Subdivision {
 
struct TexturedVertex {
    Vec3 position;
    PrimPieces::UVCoords uv;
};
 
enum Edge : unsigned {
    NoEdges = 0,
    EdgeAB = 1 << 0,
    EdgeBD = 1 << 1,
    EdgeCD = 1 << 2,
    EdgeAC = 1 << 3,
    AllEdges = EdgeAB | EdgeBD | EdgeCD | EdgeAC,
};
 
[[nodiscard]] constexpr TexturedVertex half(const TexturedVertex& a, const TexturedVertex& b) {
    return TexturedVertex{
        .position = (a.position + b.position) / 2,
        .uv = {.u = static_cast<uint8_t>((static_cast<unsigned>(a.uv.u) + b.uv.u) / 2),
               .v = static_cast<uint8_t>((static_cast<unsigned>(a.uv.v) + b.uv.v) / 2)},
    };
}
 
template <typename Decide, typename EmitQuad, typename EmitFill>
void divideQuad(const TexturedVertex& a, const TexturedVertex& b, const TexturedVertex& c,
                const TexturedVertex& d, unsigned depth, unsigned edges, Decide&& decide, EmitQuad&& emitQuad,
                EmitFill&& emitFill) {
    if ((depth == 0) || !decide(a, b, c, d, depth)) {
        emitQuad(a, b, c, d);
        return;
    }
 
    const auto ab = half(a, b);
    const auto cd = half(c, d);
    const auto ac = half(a, c);
    const auto bd = half(b, d);
    const auto center = half(ab, cd);
 
    // Every edge of this quad that borders something which may not be divided
    // is about to gain a vertex the neighbour does not have. Cover each one.
    if (edges & EdgeAB) emitFill(a, ab, b);
    if (edges & EdgeBD) emitFill(b, bd, d);
    if (edges & EdgeCD) emitFill(c, cd, d);
    if (edges & EdgeAC) emitFill(a, ac, c);
 
    const unsigned next = depth - 1;
    divideQuad(a, ab, ac, center, next, edges & (EdgeAB | EdgeAC), decide, emitQuad, emitFill);
    divideQuad(ab, b, center, bd, next, edges & (EdgeAB | EdgeBD), decide, emitQuad, emitFill);
    divideQuad(ac, center, c, cd, next, edges & (EdgeAC | EdgeCD), decide, emitQuad, emitFill);
    divideQuad(center, bd, cd, d, next, edges & (EdgeBD | EdgeCD), decide, emitQuad, emitFill);
}
 
}  // namespace Subdivision
 
}  // namespace psyqo