practice, therefore, view and projection are pre-calculated so that only the world matrix has to be adapted during the display. However, more complex transformations such as vertex blending are possible. Freely programmable geometry shaders that modify the geometry can also be executed. In the actual rendering step, the world matrix * camera matrix * projection matrix is calculated and then finally applied to every single point. Thus, the points of all objects are transferred directly to the screen coordinate system (at least almost, the value range of the axes are still -1..1 for the visible range, see section "Window-Viewport-Transformation"). Lighting Often a scene contains light sources placed at different positions to make the lighting of the objects appear more realistic. In this case, a gain factor for the texture is calculated for each vertex based on the light sources and the material properties associated with the corresponding triangle. In the later rasterization step, the vertex values of a triangle are interpolated over its surface. A general lighting (ambient light) is applied to all surfaces. It is the diffuse and thus direction-independent brightness of the scene. The sun is a directed light source, which can be assumed to be infinitely far away. The illumination effected by the sun on a surface is determined by forming the scalar product of the directional vector from the sun and the normal vector of the surface. If the value is negative, the surface is facing the sun. Clipping Only the primitives which are within the visual volume need to actually be rastered (drawn). This visual volume is defined as the inside of a frustum, a shape in the form of a pyramid with a cut off top. Primitives which are completely outside the visual volume are discarded; This is called frustum culling. Further culling methods such as backface culling, which reduce the number of primitives to be considered, can theoretically be executed in any step of the graphics pipeline. Primitives which are only partially inside the cube must be clipped against the cube. The advantage of the previous projection step is that the clipping always takes place against the same cube. Only the - possibly clipped - primitives, which are within the visual volume, are forwarded to the final step. Window-Viewport transformation In order to output the image to any target area (viewport) of the screen, another transformation, the Window-Viewport transformation, must be applied. This