FORMATS & THEIR DIFFERENCES
In addition to data compression, which reduces the build size to shorten download times for the client, Unity also compresses textures in different formats.
The purpose of this compression is to reduce VRAM usage and thus speed up rendering. These textures are not decompressed in RAM but are read directly by the GPU, which knows how to handle different compression formats.
For example, an uncompressed 4096×4096 RGBA texture can weigh around 64 MB, whereas compression can reduce it to 8–16 MB in VRAM.
Depending on the target platform, it’s important to choose a compression format suited to the device’s capabilities and compatibility:
DXT (DirectX Texture Compression): Compatible with DirectX, mainly targeting PCs and DirectX consoles (Xbox). It’s the standard for PC with decent quality.
ETC (Ericsson Texture Compression): Compatible with OpenGL ES, mainly targeting mobile devices. It’s a basic compression supported by almost all mobile devices. Note that some versions do not support alpha channels.
ASTC (Adaptive Scalable Texture Compression): Modern format compatible with OpenGL ES, Vulkan, and Metal, targeting mobile devices and modern consoles (Switch & PlayStation). It offers variable compression ratios, resulting in better visual quality at similar memory usage.
Choosing the right compression format optimizes texture reading on the GPU for the target platform.
CPU Fallback
If the GPU cannot decompress the texture format natively, the CPU handles decompression, converting it in RAM to a format the GPU can use (usually uncompressed RGBA8).
This process:
slows down performance,
consumes significantly more VRAM (textures can become 4–8 times larger than compressed).
This is why some scenes may fail to load on mobile devices if the build uses DXT: the RAM fills up with textures unreadable by the GPU, which then decompresses them into VRAM, overloading memory.
FORMAT CHOICE FOR 8 GAME LEARN WEBGL
Considering our target (schools) and the desire to support both PCs and mobile devices (tablets), the first format to discard is DXT.
Why discard DXT?
DXT targets GPUs running DirectX, which are not natively supported on mobile devices, especially low-end devices.
While DXT is fine for PCs, it makes it much harder for mobile devices to read compressed textures, which also tend to be less powerful.
The right choice: ETC2
We are left with ASTC or ETC2. At equal performance, ASTC offers the best quality-to-size ratio.
However:
ASTC is ideal for Apple devices (via Metal) and recent Android devices (>2016, via Vulkan/OpenGL ES 3).
ETC2 will fallback to RGBA on Apple devices (which are more powerful) but works perfectly on all Android devices, including low-end models.
Given that schools often use budget devices, it’s likely they have low-end Android tablets rather than iPads or recent Android devices.
Therefore, ETC2 is the safest choice for maximum compatibility across our target audience.