Screen Mode 2 Detail
Technically, mode 2 is a character mode with a colorful character set. The screen is vertically divided into three 256×64 pixel areas, each of which gets its own character set. By sequentially printing the characters 0 through 255 in all three areas, the program can simulate a graphics mode where each pixel can be set individually. However, the resulting framebuffer is non-linear.
The program can also use three identical character sets, and then deal with the screen like a text mode with a colorful character set. Background patterns and sprites then consist of colorful characters. This was commonly used in games, because to fill/scroll the entire screen, only 32×24 bytes had to be moved. Games on other home computers such as the Commodore 64 also worked on a character basis. The graphics can be drawn such that the 8×8 pixel borders are not too obvious, an art where Konami was particularly well known for their excellence.
This is the TMS9918 screen mode 2 challenge: every 8×1 pixel area has two colors, foreground and background. They may be freely picked out of the 16 color palette. But within each 8×1 pixel area, only two different colors can exist. When manipulating the screen in BASIC with the LINE command, one easily could exceed the limit of max 2 colors per 8×1 area and end up with "color spill".
In comparison, the MOS Technology VIC-II used in the Commodore 64 limited programmers to 4 colors per 4×8 fat-pixel area. This meant there was less local color pressure, but more global color pressure: while three of the 4 colors could be freely picked out of palette of 16, the remaining fourth was a universal background color.
The TMS9918 does not have any scroll registers. Scrolling must be done in software.
Read more about this topic: Texas Instruments TMS9918
Famous quotes containing the words screen, mode and/or detail:
“The screen of supreme good fortune curved his absolute smile into a celestial scream.”
—John Ashbery (b. 1927)
“That the mere matter of a poem, for instance—its subject, its given incidents or situation; that the mere matter of a picture—the actual circumstances of an event, the actual topography of a landscape—should be nothing without the form, the spirit of the handling, that this form, this mode of handling, should become an end in itself, should penetrate every part of the matter;Mthis is what all art constantly strives after, and achieves in different degrees.”
—Walter Pater (1839–1894)
“Art, it seems to me, should simplify. That, indeed, is very nearly the whole of the higher artistic process; finding what conventions of form and what detail one can do without and yet preserve the spirit of the whole—so that all that one has suppressed and cut away is there to the reader’s consciousness as much as if it were in type on the page.”
—Willa Cather (1873–1947)