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client/lobby/CBonusSelection.cpp: fix difficulty overflow in bonus UI

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Before the change campaign bonus selection screen had inconsistent
overflow behaviour for difficulty selection:

```
    0 1 2 3 4 | available buttons: '-' to decrease
      ^       |                    '+' to increase
```

Before the change:

1. If we click '+' 5 times we will end up on difficulty=4 (ok, saturated).
2. If we click '-' 5 times we will end up on difficulty=1 (unexpected, wrap around).

After the change:

1. If we click '+' 5 times we will end up on difficulty=4 (saturated).
2. If we click '-' 5 times we will end up on difficulty=0 (saturated).

The inconsistency happens because `difficulty` variable has `ui8` type
and server uses `difficulty = vstd::abetween(difficulty, 0, 4)` to
implement the saturation.

For large positive values saturation works as expected:
    vstd::abetween(difficulty=5, 0, 4) -> 4
For small values it does not:
    vstd::abetween(difficulty=-1, 0, 4) -> 4

The change makes client to avoid using negative values.
This commit is contained in:
Sergei Trofimovich 2021-07-25 11:09:00 +01:00 committed by Andrii Danylchenko
parent e4dd2f6dd8
commit e407d4e547
1 changed files with 3 additions and 1 deletions
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4
client/lobby/CBonusSelection.cpp
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@ -460,7 +460,9 @@ void CBonusSelection::increaseDifficulty()
void CBonusSelection::decreaseDifficulty()
{
CSH->setDifficulty(CSH->si->difficulty - 1);
// avoid negative overflow (0 - 1 = 255)
if (CSH->si->difficulty > 0)
CSH->setDifficulty(CSH->si->difficulty - 1);
}
CBonusSelection::CRegion::CRegion(int id, bool accessible, bool selectable, const SCampPositions & campDsc)