   what does overdraw mean
  Hi,what does overdraw mean according to an octree ?I read about to traverse an octree in front to back manner.And that there is kind of overdraw. Does it mean todraw occluded vertices more than one times or to overdraw color values, that they are too bright. ?regards,c-mos   
  I think what they are talking about is taking advantange of a z/w buffer, so you only draw a screen pixel the least amount of times.IE. if at screen position 100x100 you have 5 objects that would change that pixel, that's five times the graphics driver has to change that bit of memory. But with a z buffer if the change is behind something that is already there it will just ignore it. So the front most pixel is the only one that gets set.   ;  Hello,thanks for the fast reply and explanation. So let's say i have an octree where I only need to draw the nodes closet to the camera/view I need some technique thatdetermines  what sub-boxes are occluded the the clostest boxes, otherwiseI have an overdraw. Boxes behind the closest boxes will also be rendered i.e.that pixel.regards,c-mos ;  Overdraw occurs when you have to overwrite a previous rendered pixel, because you now have a pixel in the same screen location which is closer to the camera. Modern graphics cards have an early-Z reject, which discards pixels that would be behind pixels that were previously rendered, so if you render objects from front-to-back, you should achieve higher performance.   ;  Hello,is there an algorithm how to traveres an octree from front to back according to the current camera position ? I checked out some occlusion cullingalgorithm's to check out what bounding volume is visible. but the examples where only with one boudning volume. and only one query is possible at one time. so how could i dtermine what node is in fornt of another node when i can only query one.regards,cmos;Quote:Original post by c-mosso how could i dtermine what node is in fornt of another node when i can only query one.Generally, you don't need to - that is what the depth buffer is there for.There are a few cases where render order is important (such as when rendering transparent objects), and for those it is usually sufficient to sort objects by their distance to the camera.   ;  Hello,thanks for reply.I want to optimize my volume rendering. So Iwant to use an octree forempty space skipping/leaping(ESL). Lately I read that the disadvantage of just ESL is a so called overdraw. To overcoem this, occlusion culling is used.But then front to back oder is needed. Here is a part of the book..."A block-based rendering techique as used for empty space skipping is alsousable to prevent the renderings of blocks that are completely occluded byobjects in front of them.To exploit the occlusion for higher performance, blocks have to be sortedand rendered in a front-to-back manner. "source: http://books.google.de/books?id=lDWOu3_KGvoC&pg=PA197&dq=real-time+volume+graphics+occlusion+cullingThats why I asked for front to back and occlusion culling. Is it neccessary for occlusion culling that objects are ordered front to back ? In this case the volumeis splitted up into lot of sub-volumes. some are visible and some not.I dont know how exaclt the occlusion culling in OpenGL works but at the moment I think its sufficient to have the first visible sub-volume with respect to theviewer.regards,c-mos   