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Fix a rare chance that finalstretch displays glitchy cycle (color 7)

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It's quite rare, though possible, that during finalstretch you could see
a glitchy tileset that looked like this:

https://i.imgur.com/V7cYKDW.png

This happened because final_mapcol, the variable that controls which
color of finalstretch is rendered, could end up being 7. Normally, it's
in the range of 1..6, which perfectly correlates with the Warp Zone
tilesets in tiles2.png, and the higher the number the farther back in
the tileset it goes from the gray Warp Zone tileset. However, if it's 7,
then it'll start grabbing tiles from the Ship plus some unused blank
tiles, which does not look pretty in the slightest.

This happened because it's possible, though exceedingly unlikely, that
fRandom(), a function which returns a float between 0..1, could return
exactly 1. fRandom() calls rand(), which returns a result between 0 and
RAND_MAX, and divides it by RAND_MAX. This value is implementation
dependent, but required to be at least 32767, and on most systems is
2147483647. Even taking the value of 32767, that means there's a 0.003%
chance that you could get this glitchy tileset when the game cycled the
color in finalstretch. But of course, playing the game for long periods
of time will eventually increase this chance - cycling the color 1,000
times (around 17 minutes of playing) will result in the chance being 3%.

Then as the calculations in the finalstretch color cycling logic calls
fRandom(), then multiplies by 6 and adds 1, it was possible for
fRandom() to return exactly 1, then have
6 added to it, resulting in final_mapcol being 7.

To fix this, just decrement the multiplication by fRandom() to multiply
by 5 instead of 6. Now the only possible numbers that calculation can
produce would be 1..6.
This commit is contained in:
Misa 2022-04-09 17:31:17 -07:00
parent e47781f92f
commit b8553107ff
1 changed files with 2 additions and 2 deletions
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4
desktop_version/src/Logic.cpp
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@ -502,7 +502,7 @@ void gamelogic(void)
if (map.final_colorframe == 1) if (map.final_colorframe == 1)
{ {
map.final_colorframedelay = 40; map.final_colorframedelay = 40;
int temp = 1+int(fRandom() * 6); int temp = 1+int(fRandom() * 5);
if (temp == map.final_mapcol) temp = (temp + 1) % 6; if (temp == map.final_mapcol) temp = (temp + 1) % 6;
if (temp == 0) temp = 6; if (temp == 0) temp = 6;
map.changefinalcol(temp); map.changefinalcol(temp);
@ -510,7 +510,7 @@ void gamelogic(void)
else if (map.final_colorframe == 2) else if (map.final_colorframe == 2)
{ {
map.final_colorframedelay = 15; map.final_colorframedelay = 15;
int temp = 1+int(fRandom() * 6); int temp = 1+int(fRandom() * 5);
if (temp == map.final_mapcol) temp = (temp + 1) % 6; if (temp == map.final_mapcol) temp = (temp + 1) % 6;
if (temp == 0) temp = 6; if (temp == 0) temp = 6;
map.changefinalcol(temp); map.changefinalcol(temp);