Implementing a more flexible DIW logic

[dirkwhoffmann]

In order to get OCS/ECS behavior right for the demo mentioned in #799 (OCS must show splash screens, ECS must not), Denise needs a more accurate border processing logic:

First proposal:

Add:

• u8 borderMask[]
• bool borderMaskIsDirty
• A ring buffer for keeping track of DIWSTRT, DIWSTOP, and DIWHIGH changes. Such buffers exist already, e.g., for keeping track of color register changes.

In Denise::setDIWSTRT, Denise::setDIWSTOP, Denise::setDIWHIGH:

• Record the register change
• Mark border mask as dirty

In void Denise::hsyncHandler():

• If the border mask is dirty, update the mask.
• Draw the border (with new code using the mask).

Note: If there was a register change in line n, the border mask must be updated again in line n+1.

Deprecations:

• hflopOn, hflopOff, hpos, hflopPrev, hflopOnPrev, hflopOffPrev will be obsolete.

Pros:

• Using a border mask has precise semantics, as opposed to storing certain trigger events in multiple variables.

Cons:

• Performance may degrade a bit
  • Updating the border mask is not a big issue, as DIW register changes are rare
  • Drawing the border using a mask might impact performance because the number of memory accesses increases.

[dirkwhoffmann]

Fixed in v2.5b1