Well, I think I can explain what are lightmaps and dynamic lightmapping, at least if you can understand my English.
A lightmap is an additional texture layer applied to the surfaces (usually scenery) to enhance the appearance of the lighting in a game. The most common lighting method is the vertex lighting, which is based in calculations made in real-time even by earlier graphic adaptors, consisting in the following scheme:
o The graphics engine determines the position of a given vertex of an object, the position of a light (or more) and the intensity of the light source. Through some strange matrix calculations, it receives as result the "brightness" value of the light that reaches the vertex.
o Then, the engine makes the same calculations for the neighbouring vertices, and makes a "dithering" to interpolate the brightness values across the object's surface.
This lighting scheme has two advantages: it is fast, because the calculations required are quite simple, and it's economic (in terms of video memory), because this lighting scheme only requires three non-integer values for each vertex of the object. Perhaps, it has a great disavantage: this method is unable to represent shadow casting over an object.
When we look at a ball over a table, we can observe two things about lighting: the ball seems to be brighter in the direction of the light, AND it produces a shadow over the table, as the light was an observer that painted a darker contour in the table with a silouette of the ball. This shadowing effect can not be reproduced by common vertex lighting, so the lightmaps takes place.
Usually, the game producers use a third-part program for building the lightmaps. This program looks for all lightsources in a scene, and draws in a big (or in many small) textures the sillouettes projected by the lights. This new texture set is mixed with the original textures of the scene, giving the scene the shadows the vertex lighting was unable to reproduce.
Dynamic lightmaps are the same thing, but instead of the light calculation be made by other program, the game engine itself makes the calculations. This is necessary to reallistically make shadows for moving objects (like the game's main character, which casts a moving shadow) and for moving lights (which interfere with the entire scene lighting).
This way, the cost of speed for lightmaps is the cost of applying the additional light textures to the object. For dynamic lightmaps is the same, plus the complex calculations necessary to do the trick. In terms of memory, dynamic and non-dynamic maps are basically the same (the memory occupied by the lighting textures).
That's all, any questions, just mail-me <
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