Reproduction of perspective in cel animation 2D composition for real-time 3D rendering

Many 2D cel animations and 3DCG cel-style animations are still being actively produced in Japan. Cel animation has its own perspective, which is different from general 3D space. In this paper, we focus on the perspective generated by the compositing process and reproduce it by moving the vanishing point and adjusting the perspective strength. In the proposed method, we modify the projection matrix. This makes it possible to change the appearance of the 2D shape in real-time without changing the 3D shape of the model. The user controls the matrix using three 3D points called the vanishing guidance point, virtual viewpoint, and model focus point. A matrix is generated for each model. In addition, to operate the proposed method with the current major shading algorithms, we provide modified shadow mapping and rim lighting methods. Furthermore, we consider effective hierarchical structures for using the proposed method in general computer graphics software. The results confirm that this method reproduces the features of cel animation. Moreover, they show that the processing speed achieves the performance required for use in real-time rendering.