Blitter (Amiga)
The Blitter is an Amiga - co-processor for fast copying and moving memory contents ( bit blit ). Physically it is part of the Agnus chip.
The blitter can copy and move memory blocks at bit level quickly - and without taking up the processor time of the main processor - and also link them logically . The most obvious application is to perform appropriate operations in graphics memory . The blitter can automatically draw lines using the Bresenham algorithm .
It can simultaneously link up to three source memory areas with each other and save the result in a fourth one. The four memory areas can be organized as bitplanes of different sizes as long as the area to be scanned is the same size. Bit-by-bit shifts can be carried out without additional expenditure of time using the barrel shifter . This z. B. Punching irregularly shaped objects into an existing graphic by linking them with a mask, also known as cookie cutting ( English for "biscuit cutting").
A typical task of the blitter is to display moving objects on the screen, the so-called blitter objects . They differ from sprites in that BOBs are actually copied into the image memory, while hardware sprites are in their own registers or memory areas and are only switched into the data stream to the monitor with each image build-up.
By implementing it as dedicated hardware , it was possible to achieve a working speed in the graphics area that was not usual at the time the Amiga was presented. Previously, graphics blocks had to be moved by the main processor using a routine using two nested loops.
The blitter is still used for MFM encoding and decoding for the floppy disk drives. The coding requires three passes, the decoding one.
The name Blitter is derived from the activity of block image transfer , abbreviated as BLIT.
Jay Miner , the developer and "father" of the Amiga chipset, equipped the blitter with additional functions, such as filling out areas with bit patterns or drawing straight lines, which he saw as a reason to also " Bimmer ”for“ Bit-Mapped Image Manipulator ”.
Individual evidence
- ↑ The Blitter in the Agnus 8370
- ↑ The Amiga's blitter is also located in the Agnus chip
- ↑ What is the Blitter?
- ↑ Phillip Robinson: The Amiga's Custom Graphics Chips. (PDF; 3.4 MB) Retrieved on August 23, 2020 (English).
