CAST3D: Customizing Arbitrary 2D Assets into 3D World

High-quality 2D assets have become increasingly abundantand easy to edit, providing a rich foundation for creative content acrossart, design, and virtual environments. However, while diffusion-based 3Dgeneration has achieved remarkable progress in single-object synthesis,leveraging such 2D assets for controllable 3D composition remains a chal-lenging problem. To address this, we introduce CAST3D, a training-freeframework that enables Customized Composition in 3D: transformingarbitrary 2D assets into a coherent 3D object or scene under textualguidance. CAST3D consists of two stages: 3D Layout Hinting and Com-positional Generation. To maintain structural consistency and eliminateartifacts, we further design stochastic trajectory manipulation (STM)for structure-preserving modification and a connectivity-based pruningstrategy for clean geometry integration. Extensive experiments demon-strate that CAST3D produces semantically consistent and visually faith-ful 3D compositions, bridging 2D asset creation and 3D world synthesis.