Optical cameras give detailed images in clear waters. However, in dark or turbid waters, information coming from electro-optical sensors is insufficient for accurate scene perception. Imaging sonars, also known as acoustic cameras, can provide enhanced target details in these scenarios. In this paper, a computationally efficient 2D high-frequency, forward-looking sonar image simulator is presented. Stages and requirements of the image formation process are explained in detail. For the postprocessing of the returned sonar signals, a novel computation engine is proposed based on the geometric structures of the simulated surfaces. By treating all the continuous surfaces separately, the simulator is able to exactly calculate bright and shadowed zones in the 2D sonar image.