Fix initial GetMouseDelta on GLFW

[ve-nt]

The initial mouse delta is often very large, depending on where the cursor was before the window opened. This is because the first mouse delta is the x/y coordinates your cursor entered the screen from. This can (and often does) cause the free camera to make a sudden jump when its moved for the first time.

The solution to this is to initialize the previousPosition and the currentPosition to the same value on the first mouse input, essentially ignoring the first mouse delta.

[ve-nt]

This fixes #4654

[ve-nt]

@asdqwe
Strange, I don't get the same output when I run your test code on my machine:

Mouse start position OUTSIDE the area where window will be created:

WARNING: time:1.05   pos: 409.00 x 225.00   delta: 0.00 x 0.00
WARNING: time:1.07   pos: 409.00 x 223.00   delta: 0.00 x -2.00
WARNING: time:1.09   pos: 408.00 x 222.00   delta: -1.00 x -1.00
WARNING: time:1.10   pos: 407.00 x 220.00   delta: -1.00 x -2.00
WARNING: time:1.12   pos: 407.00 x 219.00   delta: 0.00 x -1.00
WARNING: time:1.14   pos: 407.00 x 219.00   delta: 0.00 x 0.00
WARNING: time:1.15   pos: 407.00 x 219.00   delta: 0.00 x 0.00
WARNING: time:1.17   pos: 407.00 x 219.00   delta: 0.00 x 0.00

Mouse start position INSIDE the area where window will be created:

WARNING: time:0.93   pos: 416.00 x 214.00   delta: 0.00 x 0.00
WARNING: time:0.95   pos: 416.00 x 214.00   delta: 0.00 x 0.00
WARNING: time:0.97   pos: 416.00 x 215.00   delta: 0.00 x 1.00
WARNING: time:0.98   pos: 414.00 x 216.00   delta: -2.00 x 1.00
WARNING: time:1.00   pos: 413.00 x 216.00   delta: -1.00 x 0.00
WARNING: time:1.02   pos: 411.00 x 217.00   delta: -2.00 x 1.00
WARNING: time:1.03   pos: 411.00 x 217.00   delta: 0.00 x 0.00
WARNING: time:1.05   pos: 411.00 x 217.00   delta: 0.00 x 0.00
WARNING: time:1.07   pos: 411.00 x 217.00   delta: 0.00 x 0.00

This is with me positioning my cursor, running your code, and moving my cursor slightly. Then I strip off the excess zero deltas. I'm assuming that's how you're running it as well.

[ve-nt]

Am I supposed to see that delta on the second frame without any mouse input? The first two frames always have a delta of 0.00 x 0.00 for me. I've tried triggering a delta on the second frame by moving my mouse as I start the program, but even then its just coming up zero.

I.E.

WARNING: time:0.12   pos: 400.00 x 225.00   delta: 0.00 x 0.00
WARNING: time:0.13   pos: 409.00 x 225.00   delta: 0.00 x 0.00
WARNING: time:0.15   pos: 395.00 x 222.00   delta: -14.00 x -3.00
WARNING: time:0.17   pos: 386.00 x 222.00   delta: -9.00 x 0.00
WARNING: time:0.18   pos: 380.00 x 223.00   delta: -6.00 x 1.00

If you need any info on platform differences let me know and I'll try and provide any info I can. Currently I'm building your test code by adding it to the examples/others directory. Here's the compile command from make:

gcc -o others/test others/test.c -Wall -std=c99 -D_DEFAULT_SOURCE -Wno-missing-braces -Wunused-result -O2 -D_DEFAULT_SOURCE -I. -I/home/vent/dev/repo/raylib/src -I/home/vent/dev/repo/raylib/src/external  -I/usr/local/include -I/home/vent/dev/repo/raylib/src/external/glfw/include -L. -L/home/vent/dev/repo/raylib/src -L/home/vent/dev/repo/raylib/src -L/usr/local/lib -lraylib -lGL -lm -lpthread -ldl -lrt -lX11 -latomic -DPLATFORM_DESKTOP -DPLATFORM_DESKTOP_GLFW

[ve-nt]

Here's what I'm seeing: https://www.youtube.com/watch?v=rXTMOdLJj6A

[raysan5]

This is one of the most horrible things I've seen in some time. I'm afraid I'm not adding this dirty hack to raylib... just for macOS!!! 😱

[raysan5]

Just for clarification, does it happen with other platforms?

[ve-nt]

As said in the other thread, this issue is not limited to macOS. I'm seeing the same issue on Linux.

[raysan5]

Thanks for clarification, still thinking it should be addressed at GLFW level.

[raysan5]

If the issue is related to GLFW, it should be addressed by GLFW, not hacked in raylib.