Commodore Amiga A1000, Hardware Reference Manual

Page: 193 / 380

LINE MODE
In addition to all of the functions described above, the blitter can draw patterned lines.
The line draw mode is selected by setting bit 0 (LINEMODE) of BLTCON1, which changes
the meaning of some other bits in BLTCON0 and BLTCON1. In line draw mode, the blitter
can draw lines up to 1024 pixels long, it can draw them in a variety of modes, with a
variety of textures, and can even draw them in a special way for simple area fill.
Many of the blitter registers serve other purposes in line-drawing mode. Consult Appendix
A for more detailed descriptions of the use of these registers and control bits in line-
drawing mode.
In line mode, the blitter draws a line from one point to another, which can be viewed as a
vector. The direction of the vector can lie in any of the following eight octants. (In the
following diagram, the standard Amiga convention is used, with x increasing towards the
right and y increasing down.) The number in parenthesis is the octant numbering; the
other number represents the value that should be placed in bits 4 through 2 of BLTCON1.
Figure 6-8: Octants for Line Drawing
Line drawing based on octants is a simplification that takes advantage of symmetries
between x and -x, y and -y. The following Table lists the octant number and
corresponding values:
- 184 Blitter Hardware -