Shadow Map (Shadow Map) is a technical term that is extremely important in the rendering and optimization of game graphics (technical art). An explanation of shadow drawing technology that depicts the depth (distance) of the entire scene as seen from the light (light source) in a dedicated texture and determines whether each pixel of an object is blocked from light (in the shadow).
Real-world analogy: A security system that places a "surveillance camera (shadow camera)" at the location of the light source and paints blind spots (shadows) where no light can be seen
Shadow map is a method of taking a black-and-white distance photograph (Shadow map texture) of the ``lighted area (the nearest object)'' as seen from a surveillance camera (light camera) installed at the light source.'' Afterwards, when drawing a picture with a regular camera, use this photo to check whether the place you are standing can be seen by the light source surveillance camera. If it is hidden behind another object and is a ``blind spot (in the back) that cannot be seen by the camera,'' it will be determined to be a ``shadow'' where light cannot reach and will be painted dark.
Figure: An infographic that clearly illustrates the basic processing flow and mechanism of Shadow Map (Shadow Map) in Japanese notation
Detailed mechanism and operating principle
Turn off "Cast Shadows / Receive Shadows" for small objects that do not need to cast shadows or static backgrounds, and limit the resolution (1024, etc.) and drawing distance of the shadow map and optimize it.