Why is random generation behaving differently in the downloadable engine and a source-built engine?

Manic

I'm seeing different results with the random generator in the distributed binary than I am with my compiled version of the engine with identical seeds.

I built a pretty simple test function to illustrate the problem:

var rng : RandomNumberGenerator = RandomNumberGenerator.new()
    rng.seed = 0
    for i in range(0,5):
        print(rng.randi())

Results on the distributed binary:

Results on my compiled version (both 32- and 64-bit):

Looking at the code, the only reason I can see for this discrepancy is the inc (I'm guessing increment?), as the same seed was used in both runs. The code includes (pcg.h) #define PCG_DEFAULT_INC_64 1442695040888963407ULL and I believe this value is used when instantiating the random number generator. However, I can't figure out why the random number generation would be inconsistent between different compiled versions of the engine unless that INC value differs.

I'm super confused. Any ideas?

TwistedTwigleg

This really sounds like a bug, as the exported Godot game and the Godot editor should return the same results when given the same seed. The only thing I can think of that might be contributing to this issue is if code in the random number generator class changed between versions.

I would check to see if there is an open issue on the Godot GitHub repository for this issue, and if not opening a issue.

(Side note: Welcome to the forums!)

Manic

Turns out that I wasn't compiling at the right commit like I thought I was. When compiled at commit 66baa3b (the commit for 3.1.1), the results are identical, as expected:

running with godot.windows.tools.64.exe:
OpenGL ES 3.0 Renderer: GeForce GTX 1060/PCIe/SSE2
seed = 0
1613493245
3894649422
2055130073
2315086854
2925816488
3443325253
1644475139
428639621
1241310737
3521718650
338531392

running with Godot_v3.1-stable_win64.exe:
OpenGL ES 3.0 Renderer: GeForce GTX 1060/PCIe/SSE2
seed = 0
1613493245
3894649422
2055130073
2315086854
2925816488
3443325253
1644475139
428639621
1241310737
3521718650
338531392

running with Godot_v3.1.1-stable_win64.exe:
OpenGL ES 3.0 Renderer: GeForce GTX 1060/PCIe/SSE2
seed = 0
1613493245
3894649422
2055130073
2315086854
2925816488
3443325253
1644475139
428639621
1241310737
3521718650
338531392

So, I messed up my versioning at compile time, and apparently something related to random number generation changed between 66baa3b and 2c6daf73. Anyway, everything's solved now.

(Side note: Thank you! It's pretty nice here.)