Function ImBezierCubicClosestPointCasteljauStep

tutorials/common/imgui/imgui.cpp:1524–1555

Closely mimics PathBezierToCasteljau() in imgui_draw.cpp

// Closely mimics PathBezierToCasteljau() in imgui_draw.cpp
static void ImBezierCubicClosestPointCasteljauStep(const ImVec2& p, ImVec2& p_closest, ImVec2& p_last, float& p_closest_dist2, float x1, float y1, float x2, float y2, float x3, float y3, float x4, float y4, float tess_tol, int level)
{
    float dx = x4 - x1;
    float dy = y4 - y1;
    float d2 = ((x2 - x4) * dy - (y2 - y4) * dx);
    float d3 = ((x3 - x4) * dy - (y3 - y4) * dx);
    d2 = (d2 >= 0) ? d2 : -d2;
    d3 = (d3 >= 0) ? d3 : -d3;
    if ((d2 + d3) * (d2 + d3) < tess_tol * (dx * dx + dy * dy))
    {
        ImVec2 p_current(x4, y4);
        ImVec2 p_line = ImLineClosestPoint(p_last, p_current, p);
        float dist2 = ImLengthSqr(p - p_line);
        if (dist2 < p_closest_dist2)
        {
            p_closest = p_line;
            p_closest_dist2 = dist2;
        }
        p_last = p_current;
    }
    else if (level < 10)
    {
        float x12 = (x1 + x2)*0.5f,       y12 = (y1 + y2)*0.5f;
        float x23 = (x2 + x3)*0.5f,       y23 = (y2 + y3)*0.5f;
        float x34 = (x3 + x4)*0.5f,       y34 = (y3 + y4)*0.5f;
        float x123 = (x12 + x23)*0.5f,    y123 = (y12 + y23)*0.5f;
        float x234 = (x23 + x34)*0.5f,    y234 = (y23 + y34)*0.5f;
        float x1234 = (x123 + x234)*0.5f, y1234 = (y123 + y234)*0.5f;
        ImBezierCubicClosestPointCasteljauStep(p, p_closest, p_last, p_closest_dist2, x1, y1, x12, y12, x123, y123, x1234, y1234, tess_tol, level + 1);
        ImBezierCubicClosestPointCasteljauStep(p, p_closest, p_last, p_closest_dist2, x1234, y1234, x234, y234, x34, y34, x4, y4, tess_tol, level + 1);
    }
}

// tess_tol is generally the same value you would find in ImGui::GetStyle().CurveTessellationTol
// Because those ImXXX functions are lower-level than ImGui:: we cannot access this value automatically.