nine_patch.hpp

#pragma once
 
#include <QVector2D>
#include <QVector4D>
 
#include "qml_material/scenegraph/mesh/quad.hpp"
 
namespace qml_material::sg::mesh
{
 
template<class Vertex, class CornerFillFn>
void build_nine_patch(Vertex* v, QVector2D size, QVector4D radius, CornerFillFn corner_fill) {
    constexpr int u = 6;
 
    struct cell {
        QVector2D origin;
        QVector2D size;
    };
    const cell corners[4] = {
        { { 0.0f, 0.0f }, { radius[0], radius[0] } },
        { { size.x() - radius[1], 0.0f }, { radius[1], radius[1] } },
        { { 0.0f, size.y() - radius[2] }, { radius[2], radius[2] } },
        { { size.x() - radius[3], size.y() - radius[3] }, { radius[3], radius[3] } },
    };
 
    for (int i = 0; i < 4; ++i) {
        corner_fill(v + u * i, i, corners[i].origin, corners[i].size);
    }
 
    // Edge and center cells: stitched by copying corner vertices.
    // See ASCII diagram in docs; vertex indices hand-verified against the pre-refactor
    // src/scenegraph/geometry.cpp::update_rectangle_geometry.
    quad(v + u * 4, v[5],         v[u + 0],     v[4],         v[u + 2]);     // Top
    quad(v + u * 5, v[u * 2 + 1], v[u * 3 + 0], v[u * 2 + 4], v[u * 3 + 2]); // Bottom
    quad(v + u * 6, v[3],         v[4],         v[u * 2 + 0], v[u * 2 + 1]); // Left
    quad(v + u * 7, v[u + 2],     v[u + 4],     v[u * 3 + 0], v[u * 3 + 1]); // Right
    quad(v + u * 8, v[4],         v[u + 2],     v[u * 2 + 1], v[u * 3 + 0]); // Center
}
 
} // namespace qml_material::sg::mesh