What's a Texture2DArray?

GPU texture with multiple slices indexed by a third coordinate. Common for terrain layers, sprite atlas variants, palette swaps. Sample via tex.Sample(sampler, float3(uv, slice)).

Why does it fail on mobile?

Format compatibility (some Android GPUs lack ASTC array support), older OpenGL ES drivers with broken layered texture impls, and missing mipmaps causing samplers to read undefined results.

Use Frame Debugger to inspect bound textures. Check texture format on device (Texture2DArray.format). Test sampling each slice in a debug shader to find which fail.

Fix: Unity Texture2DArray Element Zero on Mobile

Quick answer: Use ASTC or ETC2 compression supported by your minimum Android SDK. Generate mipmaps. Sample with explicit LOD on weak GPUs.

A terrain shader uses a Texture2DArray for 8 ground layer textures. On editor and high-end Android, renders fine. On older Android (Adreno 5xx), the lowest slice reads black, breaking the terrain.

Check Format Support

Debug.Log($"Format: {arr.graphicsFormat}");
Debug.Log($"Supports sampling: {SystemInfo.IsFormatSupported(arr.graphicsFormat, FormatUsage.Sample)}");

Some GPUs report supported but have driver bugs at runtime. Test on actual hardware.

Format Choice

For Android:

ETC2_RGBA8: universal on OpenGL ES 3.0+. Safe baseline.
ASTC_HDR / LDR: better quality, requires OpenGL ES 3.2 or extension.
RGB Compressed BC*: desktop only, don’t use on mobile.

Import Settings: Default platform uses BC; Android override to ETC2_RGBA8 for safety.

Mipmaps Required

Some sampler implementations on mobile return zero when sampling a mip level that doesn’t exist. Set Generate Mip Maps on import, or build the array with mipmaps in code:

arr = new Texture2DArray(1024, 1024, slices, TextureFormat.ETC2_RGBA8, true);

Explicit LOD in Shader

Force a known mip on shaky drivers:

float4 col = SAMPLE_TEXTURE2D_ARRAY_LOD(_TerrainArray, sampler_TerrainArray, float3(uv, slice), 0);

Bypasses derivative-based LOD selection that some drivers mishandle for array textures.

Frame Debugger Inspection

Window → Analysis → Frame Debugger on device. Step to the draw call; inspect the Texture2DArray binding. Verify all slices have data — not just slice 0 black.

Verifying

Deploy to a low-end Android device. Terrain renders with all 8 layers visible. No black areas. Cross-test on iOS and high-end Android to ensure no regressions.

“Mobile GPU drivers vary. Standard formats, mipmaps, explicit LOD: three tools that fix most array-texture bugs.”

For wide device support, ETC2 with mips on Android baselined to API level 24 covers ~98% of active phones. Test on Mali 4xx/6xx and Adreno 5xx—those expose driver quirks fastest.