>> Just like PowerVR's gfx chips with tile rendering, which process >> the z-buffering for the screen in small blocks and render only >> what is visible.
This is common practice across all modern cards. A hierarchical approach is taken - there is a full z-buffer for all pixels, then a version with the farthest z for each group of 4 pixels, a version with the farthest z for each group of 16, and so on, with the effect that large portions of triangles can often be thrown away, especially if the programmer has followed the modern convention of doing a loose front to back sort before drawing. >If you >store a table of square roots for the Pythagoras, it speeds up >nicely (big table, but hell, you'll already be storing perspective >correction tables and SINE tables, so you won't be bothered about >memory). There is an entire web page somewhere dedicated to getting fast sqrts. I've seen one which uses only a 256 or 512 byte table but can do a 16bit sqrt in less than 100 cycles. >You could also try doing a view frustum cull beforehand to reduce >the list to just visible objects, or take the easy route and just >make sure the objects are forward of the camera. You count the >T-States and take your choice! Elite has the very bad habit of culling all objects that even intersect the front plane. You don't usually notice, but try flying over the front of a space station. >Right now I'm tinkering with adding 'building block' sector coords >to each object, like a vague grid reference. Then you could easily >apply a 'bitmapped' view frustum to search the main area for >potentially visible objects. I'm not convinced yet, but it may >work.... An octree does more or less this. Its a recursive structure, with the parent being a rectangle (the root node being the rectangle enclosing 'all' of space) and the children being 8 smaller rectangles. The game is that if a particular parent is entirely outside of the view frustum then you don't recurse, and if it is entirely inside the view frustum then you draw everything immediately. If it intersects the frustum (and the node has children) then you recurse. By the way, with respect to Elite, I once partially reverse engineered the ZX Spectrum version, which is visibly identical to the SAM version implying that all that is running is the Spectrum code and a mode 1 screen. In which case we are seeing the following abuses of the SAM hardware : - mode 1 display, with obvious effects on running speed - software double buffering, even though in the SAM (and 128kb Spectrum, I believe) this can be achieved in hardware If someone is planning on writing a new implementation of Elite for the SAM, then it might be worth noting that the original BBC Micro 6502 source has been released by Ian Bell but is nearly illegible. It has subsequently been converted into C using the Allegro graphics library by Christian Pinder, the source for which is available via http://www.newkind.co.uk (see Elite : The New Kind, rather than the other). I contributed the anti-aliased drawing routines, and a few other modifications regarding subpixel accuracy for that purpose! -Thomas When words aren't enough - Vodafone live! A new world of colour, sounds, picture messages and information on your mobile. <a href="http://ad.doubleclick.net/clk;4909903;7724245;q?http://www.vodafone.co.uk/live";> Click here</a> to find out more.
