Godot Version
4.4.1 ~ 4.8 dev6
Question
Any texture used in decals will result in doubled video memory usage - regardless of whether it has been compressed or not. (In the picture, you can see the changes of VRAM after I increased the resolution of the four textures used for Decal from 2x2 to 2K, )
Usually, an uncompressed 1K resolution texture (with alpha channel) occupies 4 MB of video memory. This is normal for general materials, and after compression, it usually only occupies 512 KB (without Mipmaps). However, when the same texture is used in a Decal node, its video memory occupation will reach about 25 MB, regardless of whether the texture is compressed or not.
To be precise, each different 1K texture used for decals will occupy an additional approximately 21 MB, which means that a decal node using 4 different 1K textures will result in a complete additional memory usage of 85 MB If it is a 2K texture, then each texture occupies an additional 85 MB<4 different 2K textures occupy an additional 340 MB of video memory, and 10 such stickers can occupy up to 3.5 GB of video memory>
The 1K texture only occupies 2.7 MB of basic video memory after compression, while the 2K texture occupies 4 times more. This is the actual video memory usage of a Stranded Material3D loaded with four identical textures
In addition, it is worth mentioning that the textures used in the light projector also have the same additional memory occupation, so this problem may exist in more than one place.
Replication method: Create a MeshInstance3D → create a Decal → create a material for MeshInstance3D → create a GradientTexture2D for albedo_texture in the material of MeshInstance3D, similarly, create 4 new GradientTexture2D for the 4 textures of Decal → set the resolution of all GradientTexture2D to 2x2.
After preparation, open Monitors in Debugger and check Video Mem, Texture Mem, Buffer Mem. Pin this window and run the scene
In the running state, modify the albedo_texture or textures used for Decal, and observe the changes in Video Mem, Texture Mem, and Buffer Mem