The eddh_PatDestBlt function handles a BitBlt of a pattern onto the display. Structurally, it is very similar to eddh_SrcDestBlt in that it enumerates through the clipping regions passed to it, and for each rectangle that the operation intersects, it calls one of two routines: PatDestBltColor or PatDestBlt1To8. PatDestBltColor performs patblts where the pattern is taken from a color bit map. The most common color pattern blt is the 2x2 dither used to paint the desktop in 8-bit-per-pel modes. Even portions of windows that appear to be white are, in fact, dithered. The pattern bit map may need to be rotated to align with the destination. If this is the case, PatDestBltColor builds a rotated copy of the pattern in the Phunk. When built, the pattern is copied into off-screen VRAM. The pattern is then tiled across the destination with successive hardware blts. In the case of a pattern copy, the first row of the destination is built, and then used as the source for the successive blts. This operation could be performed more efficiently on S3 chips by detecting patterns that are up to 2x2, 4x4, or 8x8, putting them in off-screen VRAM, and performing blts with them with a single S3 pattern-blt command.

PatDestBlt1To8 handles monochrome patterns. It calls either PattBlt24, for the 24 bpp case, PattBlt1x8, or PattBlt8x8. PattBlt1x8 is a special case routine that handles 1 high by 8 wide monochrome patterns. This special case routine is one of the few pattern blts that the original 8514/A could perform in a single operation. The S3 driver performs this operation as a monochrome expansion through the pel port. If your hardware does not handle 1x8 monochrome blts, do not implement this special case routine.

PattBlt8x8 controls the more general case of 8x8 monochrome pattern. The S3 chip can perform this as a single-blt operation. For the S3 driver, the PattBlt8x8 aligns the pattern, copies it into off-screen VRAM, and then issues a command to the S3 chip to do the pattern blt.

Because the various S3 chips do not directly support packed 24-bit-per-pel modes, PattBlt24 processes more than PattBlt8x8. It expands the pattern into off-screen memory and then repeatedly blts this off-screen pattern onto the display using a VRAM-to-VRAM copy blt. After it has filled a single row of the pattern, it then repeatedly blts that entire row, doubling the height of the source each time. For example, if the pattern is 1 pel high by 8 wide, PattBlt24 first builds a row of the pattern 1 pel high. It then copies that row to the second row. Next, it copies both the first and second rows to the third and fourth rows. It then copies the first four rows to the next four. It then continues to double until it has filled the destination rectangle.