Which Mesa to install to a system that currently uses i915 (and xserver-xorg-video-intel)?

Which Mesa to install to a system that currently uses i915 (and xserver-xorg-video-intel)?

I read that contemporary versions may drop the i915 driver and replace it with i915g. Then some sources said that updating is at one's own risk.

1. So should I install the Amber Branch instead?

2. Does the Ubuntu version used matter?

3. Does one need to uninstall the previous drivers?

In particular, I have the Intel HD 4000.

BTW, I also get with vulkaninfo the following outputs:

MESA-INTEL: warning: Ivy Bridge Vulkan support is incomplete
WARNING: lavapipe is not a conformant vulkan implementation, testing use only.
VK_LAYER_MESA_overlay (Mesa Overlay layer) Vulkan version 1.1.73, layer version 1:
WARNING: lavapipe is not a conformant vulkan implementation, testing use only.
    driverName         = Intel open-source Mesa driver
    driverInfo         = Mesa 21.2.6
    driverName                                           = Intel open-source Mesa driver
    driverInfo                                           = Mesa 21.2.6
    driverInfo         = Mesa 21.2.6 (LLVM 12.0.0)

MESA-INTEL: warning: Ivy Bridge Vulkan support is incomplete
WARNING: lavapipe is not a conformant vulkan implementation, testing use only.
WARNING: lavapipe is not a conformant vulkan implementation, testing use only.
    conformanceVersion = 1.2.0.0
    conformanceVersion                                   = 1.2.0.0
    conformanceVersion = 1.0.0.0

While the reference to i915 is related to:

sudo lshw -c video
  *-display                 
       description: VGA compatible controller
       product: 3rd Gen Core processor Graphics Controller
       vendor: Intel Corporation
       physical id: 2
       bus info: pci@0000:00:02.0
       version: 09
       width: 64 bits
       clock: 33MHz
       capabilities: msi pm vga_controller bus_master cap_list rom
       configuration: driver=i915 latency=0
       resources: irq:33 memory:d4000000-d43fffff memory:c0000000-cfffffff ioport:4000(size=64) memory:c0000-dffff

The Intel HD Graphics 4000 iGPU uses i965 as its OpenGL driver, not i915/i915g. In recent versions of Mesa, i965 has been replaced with Crocus, which is well-tested on 4xxx series iGPUs.

Additionally, it appears you are on Ubuntu 20.04, which ships with a Mesa version from before the legacy drivers (including i965) were moved to Amber. The legacy drivers were dropped in Mesa 22.0, while Ubuntu 20.04 has Mesa 21.2, so Amber will not change anything here anyway.

TL;DR no, you don't need to install the Mesa Amber drivers. They are only required for extremely ancient graphics cards. Ubuntu is using the best configuration for your Intel GPU out of the box. Updating to Ubuntu 22.04 or updating your Mesa driver will get you the newer Crocus driver, which can improve performance and support newer versions of OpenGL.

Side note: You may be confused that your GPU does indeed use i915, but i915 is also the name of the Intel kernel graphics driver, which is different from the i915/i915g OpenGL drivers. This driver is the same for all Intel GPUs and it is part of the Linux kernel, not Mesa (https://blogs.igalia.com/itoral/2014/07/29/a-brief-introduction-to-the-linux-graphics-stack/).

I've personally used Crocus on both Sandy Bridge and Ivy Bridge, and it really works well and can basically run games up to limits of the hardware (Ironically on Sandy Bridge, no DXVK but wine through wined3d will run some D3D11 games, while in Windows it only supports D3D10.) As you get to more and more graphically demanding games, you hit the point where frame rate on "low settings" is too low well before you hit the point where the games needs newer shader models and such than wine/wined3d/Crocus manage to provide.

On the even older Intel GPUs that do use Amber.. my Dad uses a desktop with a Core 2 Quad in it, and I can say Amber worked on it, but even just running glxgears (with vsync disabled) the GPU is so slow (and modern software renderer fast enough) that it's faster to not install it and let a core or so of CPU do the OpenGL work. (This is not a fault of Amber, those oldest Intel GPUs would just about max out running the screensavers.) The software renderer also supports a newer OpenGL version than the 1.4/2.1 that the hardware does. I removed Amber.