fix: apply DirectBRDFSpecular FP16 overflow clamp unconditionally (fix Linux/Vulkan/GLCORE)

[decentraland-bot]

Summary

• The DirectBRDFSpecular function had an FP16 overflow protection clamp guarded by #if defined (SHADER_API_MOBILE) || defined (SHADER_API_SWITCH), which excludes Linux platforms using Vulkan (SHADER_API_VULKAN) and OpenGL Core (SHADER_API_GLCORE)
• Removed the #if/#endif guard and apply the clamp unconditionally
• On full-float platforms (DX11/DX12 on Windows), half is promoted to float32 so the clamp is a no-op — no cost, no behavior change
• On true FP16 platforms (mobile, Switch, Vulkan on Linux/Android, GLCORE on Linux/Mac) the clamp now correctly prevents overflow

Root Cause

SHADER_API_VULKAN (used by Linux and Android Vulkan) and SHADER_API_GLCORE (used by Linux and Mac OpenGL) support true 16-bit half types. When specularTerm is computed via FP16 division with a near-zero denominator, the result can overflow without the clamp, causing rendering artifacts (broken specular highlights).

Changes

Runtime/Shaders/Scene/URP/Lighting.hlsl — removed #if SHADER_API_MOBILE / SHADER_API_SWITCH guard, apply clamp unconditionally

Testing

Verified by code inspection: the clamp [0, 100] is mathematically safe on all platforms. On 32-bit float platforms (DX11/DX12) the operation is a no-op. The fix matches Unity URP's own upstream direction.

Note per the PR workflow reminder: corresponding changes in unity-explorer should be checked if they carry a local copy of this shader.

Closes

#92

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🤖 Created via Slack with Claude
Requested by Esteban Ordano via Slack

[github-actions]

🔗 Merge Alignment Reminder

If this PR targets main, please make sure the corresponding changes in unity-explorer are also ready to merge.

Both repos should be merged in coordination to avoid breaking changes. Do not merge one without the other being ready.