1.1 KiB
1.1 KiB
perform a shifted blit
Extending 007.masked_blit, we now add the capability to blit to non word aligned columns.
The blitter can only address word aligned screen positions. This makes drawing something on a non word aligned boundary slightly more complex.
So the algorithm for drawing to non word aligned boundaries is as follows:
- The destination address is the word aligned address to the left of the desired position.
- Command the blitter to blit an extra word to the right of our blitter object.
- We mask the trailing word of each line to prevent the extra word from being blit.
- We right shift the data by the difference in bits between the desired column and the word aligned column from (1).
- We make the line modulos #-2 so blitter object data is correctly fetched.
screenshot
