Controllable image structure editing has attracted increasing attention. While recent interactive point-based methods are convenient and realistic, they often lack fine-grained control over localized content. Partial sketches provide a simple yet expressive interface for local structure manipulation. However, existing partial-sketch-based manipulation methods relying on generative adversarial networks (GANs) suffer from limited generalization and fidelity. Moreover, although diffusion-based adapters excel at global conditioning (e.g., edge maps), localized editing with partial strokes remains challenging due to two key issues: effectively injecting sparse stroke conditions during denoising and preserving non-edited regions to avoid unintended changes. To address these challenges, we propose DiffStroke, a mask-free framework for localized image manipulation with partial sketches. We introduce trainable Image-Stroke Fusion (ISF) blocks to fuse source images and strokes at the feature level, enabling precise local shape control while maintaining appearance consistency. We further develop a self-supervised mask estimator to protect irrelevant regions without manual input. Specifically, we leverage Tweedie's formula to estimate a clean latent image from noisy latents, blend the denoised result with the source, and train the mask estimator by minimizing the error between the blended latent and the target latent. Experiments on natural and facial images demonstrate that DiffStroke outperforms state-of-the-art methods on both simple and complex stroke-based editing tasks. DiffStroke can also be combined with text prompts to produce diverse and creative results. Code is available at https://github.com/CMACH508/DiffStroke.

Recent advances in vision-language models have facilitated progress in sketch generation. However, existing specialized methods primarily focus on generic synthesis and lack mechanisms for precise control over sketch styles. In this work, we propose a training-free framework based on diffusion models that enables explicit style guidance via textual prompts and referenced style sketches. Unlike previous style transfer methods that overwrite key and value matrices in self-attention, we incorporate the reference features as auxiliary information with linear smoothing and leverage a style-content guidance mechanism. This design effectively reduces content leakage from reference sketches and enhances synthesis quality, especially in cases with low structural similarity between reference and target sketches. Furthermore, we extend our framework to support controllable multi-style generation by integrating features from multiple reference sketches, coordinated via a joint AdaIN module. Extensive experiments demonstrate that our approach achieves high-quality sketch generation with accurate style alignment and improved flexibility in style control. The official implementation of M3S is available at https://github.com/CMACH508/M3S.