Searching for an X-Ray resource pack for Minecraft 1.12.2 usually means you're looking for a way to see through blocks like stone and dirt to find ores (diamonds, gold, etc.) more easily.
For optimal performance, many of these packs, such as the popular Xray Ultimate, require users to disable "Smooth Lighting" in their video settings to ensure ores are fully illuminated underground. Installation and Usage x ray 1.12 2 resource pack
Prerequisites:
An X-Ray resource pack is a modified set of textures that makes certain blocks (like stone, dirt, and deepslate) fully or partially transparent, while leaving valuable ores (diamonds, gold, emeralds, etc.) visible. This allows a player to see ore veins through the ground, essentially “cheating” to find resources instantly. Searching for an X-Ray resource pack for Minecraft 1