harry@ruuinf.UUCP (Harry van Stedum) (12/24/88)
Hi there, I'm writing a couple of routines for manipulating bitmaps. I've now come to the hardest part, namely, rotating the maps. I've read some postings about it in this newsgroup (CORDIC, hardware solutions), but most solutions deal with pointmaps, i.e. maps of all coordinates of the pixels. My def of a bitmap is an array of chars, where a char consists of 8 bits, each bit standing for a pixel. So rotating this bitmap-type cannot be done by just "pushing" all coordinates through an apropriate matrix (with cos, sin etc.), 'cause you can't access a pixel directly and you don't know the coordinates of a pixel. I would like suggestions, algorithms, etc., to do the nasty rotating. I was thinking of something recursive, mainly for its speed and efficiency (I may be wrong on this!). At this moment I have some ideas: rotating through double shearing and transposing the map, but these operations are quite time-consuming (...) and not the most efficient (read: fast). References are also welcome, but most stuff I read sofar, deals with special equipment. I've got to do it software-matic, on an Atari 1040ST (argh!). Thanks in advance && best wishes for '89 !!! Harry ------------------------------------------------------------------------------- Harry van Stedum UUCP:...!hp4nl!ruuinf!harry Dept. of Computer Science Univ. of Utrecht "I can't change the world, Padualaan 14, P.O.Box 80.089 but I can change the world in me, 3508 TB Utrecht if I rejoice"-U2 Holland -------------------------------------------------------------------------------
turk@Apple.COM (Ken "Turk" Turkowski) (12/31/88)
The best techniques are the 2- and 3-pass methods described in: Alvy Ray Smith, "3-D Transformations of Images in Scanline Order", SIGGRAPH '80 proceedings, pp. 279-285. Steve Gabriel and Larry Evans, Method and System for Spacially (sic) Transforming Images (ADO patent), #4,631,750, December 23, 1986. Alan Paeth, "A Fast Algorithm for General Raster Rotation", Graphics Interface '86 Proceedings, pp. 77-81. Ken Turkowski @ Apple Computer, Inc., Cupertino, CA Internet: turk@apple.com Applelink: Turkowski1