pff@beach.cis.ufl.edu (Pablo Fernicola) (08/28/89)
Are overlays and underlays available on the Personal Iris? The info on page 11-1 of the Graphics Library User's Guide is not clear about it. If they are not available, can I achieve the same results using writemasks? Thanks! Pablo pff@beach.cis.ufl.edu -- pff@beach.cis.ufl.edu Pablo Fernicola - Machine Intelligence Laboratory - UF "That has nothing to do with computers; it is software."
woo@sharona.csd.sgi.com (Mason Woo) (08/29/89)
In article <20790@uflorida.cis.ufl.EDU>, pff@beach.cis.ufl.edu (Pablo Fernicola) writes: > Are overlays and underlays available on the Personal Iris? > If they are not available, can I achieve the same results using writemasks? If you have a 24 bitplane Personal IRIS, you also get 2 bitplanes of overlay/underlay (as well as 2 bitplanes for the window manager overlays). If you have the entry-level 8 bitplane machine, I believe (someone at SGI correct me if I'm wrong!) you only get the 2 bitplanes for the window manager overlays. You cannot achieve the same results with writemasks with an RGB application. RGBwritemask would preserve bitplanes which would be directly used to display colors. You couldn't draw into these bitplanes and then overlay the other RGB bitplanes. The writemask command can be used for overlays/underlays with a color map application. However, you will need to alter the loaded colors in your color map to achieve the desired effect. Each bitplane used doubles the number of colors available for overlays/underlays (actually 2 to the N minus 1), but also halves the number of colors available for the normal drawing. For example, with an 8 bitplane system, if 3 are used for overlays, then there are 7 overlay colors and 32 (2 to the 5th) standard image colors. Double buffering makes a large difference when using writemasks. If you use the 2 special bitplanes provided on the 24-bitplane Personal IRIS, then the static overlay/underlay is only drawn once, and swapping buffers will have no effect on the overlay/underlay. If you use writemask, then the bitplanes are reserved in both buffers. Commercial message: Overlays and underlays are currently discussed in the first IRIS 4D Graphics course. Writemasks are not discussed in neither the Graphics nor the Advanced Graphics courses, but we are thinking about including them when we revise the courses. -- Mason ("sex, lies, and workstations") Woo (415) 962-3314 Silicon Graphics Computer Systems Internet: woo@SGI.COM UUCP: {ames,ucbvax,decwrl,sun}!sgi!woo
tjh@bu-cs.BU.EDU (Timothy Hall) (08/29/89)
In article <41054@sgi.sgi.com> woo@sharona.csd.sgi.com (Mason Woo) writes: >In article <20790@uflorida.cis.ufl.EDU>, pff@beach.cis.ufl.edu (Pablo Fernicola) writes: >> Are overlays and underlays available on the Personal Iris? >> If they are not available, can I achieve the same results using writemasks? > >You cannot achieve the same results with writemasks with an RGB application. >RGBwritemask would preserve bitplanes which would be directly used to >display colors. You couldn't draw into these bitplanes and then overlay >the other RGB bitplanes. > True, but if one is willing to give up the LSB of the RGB planes it is possible to fake 3 more overlay planes. So you could use RGBwritemask( 0xfe, 0xfe, 0xfe ) when writing to the RGB planes and RGBwritemask( 1, 1, 1 ) when writing to the "overlays". Use the gammaramp function to set what your overlay colors will be. -Tim tjh@bu-pub.bu.edu
zombie@voodoo.UUCP (Mike York) (08/29/89)
In article <41054@sgi.sgi.com> woo@sharona.csd.sgi.com (Mason Woo) writes: >Commercial message: Overlays and underlays are currently discussed in the >first IRIS 4D Graphics course. Writemasks are not discussed in neither the >Graphics nor the Advanced Graphics courses, but we are thinking about >including them when we revise the courses. When I took the beginning gl class 4 years ago, writemasks were covered thoroughly. Now, when we we get a new person in our group and send them to the basic gl class, no writemasks. Writemasks are essential for our application. There are things you can do with writemasks in doublebuffer mode that can't be done with underlays/overlays. Writemasks should be covered in the basic gl class. -- Mike York Boeing Computer Services, Renton, Washington (206) 234-7724 uw-beaver!ssc-vax!voodoo!zombie