Note: most likely this technique is not needed for simple games. So, it's not mandatory for jr-devs.
SubSource can be chosen in the Flag column of the Achievement Editor
Works similarly to
Add Source, but the
Sub Source flag makes the value in the memory address have a negative value.
Sub Source is NOT a subtraction flag. It just makes the value be negative.
Note 2: The final line (without
Add Source or
Sub Source) is still added for the final comparison.
AddSource usecase example, if we replaced it with the
Sub Source and with the same values (
value(0x8010) = 1 and
value(0x8020) = 2), the comparison would be
-1 + 2 > 0, or
1 > 0.
Using SubSource to Count Specific Incrementslink
SubSource can also be used to track specific increases in addresses. The conditions below states that the current value in address
0x0080dc less the value in the previous frame in the same address must be equal
2. Effectively, this means that the condition is true whenever the value in address
0x0080dc increases by exactly two.
Checking for a negative resultlink
If the result of your Sub Source operation is a negative number, it is possible to check for it. This is how negative numbers are represented:
- and so on...
So, let's say you want to check if
value(0x8010) = 1 minus
value(0x8020) = 2 equals
-1. This is how you would do it:
-2 + 1 = -1, which is true.
Advanced: it is also possible to use straight negative numbers in the left section of your Sub/Add Source operations. To do so, remember to change the Type from
Value, and use the values as explained above, such as
-29, for example:
-2 + (-27) = -29, which is
-2 - 27 = -29, which is true.
Take care, though, if you use a straight negative number in a Sub Source flag, it will result in a double negative, turning the number back to positive. Take a look:
- (-2) + (-27) = -29, which is
2 - 27 = -29, which is
-25 = -29, which is false.
Last 10 changes on this page:
[2020-01-15 08:23] meleu:better example of a negative number
[2019-12-31 12:14] meleu:cosmetic
[2019-02-17 23:42] meleu:better example for "Using SubSource to Count Specific Increments"
[2019-02-17 21:05] meleu:cosmetic
[2019-02-14 10:10] meleu:fix broken link
[2019-02-12 13:25] meleu:add heading to "Using SubSource to Count Increments"
[2019-02-12 13:18] meleu:fix broken link
[2019-02-12 09:37] meleu:Updated SubSource (markdown)