// 智能拼版算法 (PHP)
public function calculateImposition($width, $height, $qty) {
    // 获取大版纸张尺寸 (例如: 889x1194)
    $paperSize = $this->getPaperSize('da_du'); 
    
    // 计算横排与竖排的最大拼版数
    $numX = floor(($paperSize['w'] - 10) / ($width + 2)); // 含出血
    $numY = floor(($paperSize['h'] - 10) / ($height + 2));
    
    $totalOnSheet = $numX * $numY;
    
    // 计算所需大版纸张张数
    $totalSheets = ceil($qty / $totalOnSheet);
    
    // 阶梯报价逻辑
    $printPrice = $this->getPriceStep($totalSheets);
    
    // 后道工艺费 (例如覆膜)
    $filmPrice = $totalSheets * $this->filmRate;
    
    return [
        'layout' => "{$numX}x{$numY}",
        'sheets_needed' => $totalSheets + $this->lossRate, // 含损耗
        'total_price' => $printPrice + $filmPrice
    ];
}