The fragment Z is the PSP's Z / 65536, and flat draws land exactly on an
integer Z. floor(z * 65535) put that Z - Z/65536 just above the boundary, so
float error (which differs with W) could drop it by one: Patlabor redraws a
HUD icon at the same depth with GEQUAL, and the second draw failed on
Vulkan. Floor Z + 0.01 instead, and store Z / 65535, as clears and the depth
clamp path do. Also fixes Heroes Phantasia #6485.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
