New Apple Silicon M4 and M5 HiDPI Limitation on 4K External Displays

Original Article ↗ Hacker News Discussion ↗

Nature of the issue

  • Discussion centers on new M4/M5 Macs limiting HiDPI framebuffer size on 4K external displays.
  • Previously, some users rendered at 8K (e.g., 7680×4320) and downscaled to 4K to improve text quality; on M4/M5 this appears capped to ~1.75× rather than 2×, breaking that setup.
  • The regression mainly affects users forcing “HiDPI at native 4K” via tools, not default macOS scaling.

Why people were doing this

  • macOS text at 1× (“LoDPI”) is widely described as fuzzy/harsh, especially after Apple removed subpixel antialiasing.
  • Supersampling (rendering at 2× and downscaling) produces noticeably better text, especially on 4K 27–32" and ultrawide monitors.
  • Some consider this a necessary workaround on non-Apple displays; others call it an odd, power-hungry edge case.

User experiences and disagreement

  • Some M4/M5 owners strongly notice blur or fuzziness on 4K/5K2K/dual-4K setups despite experimenting with BetterDisplay.
  • Others report no visible difference between M2 and M4/M5 on 4K screens, or say they can still use 1080p@2× fine.
  • A number of commenters argue 4K at 27–32" is not true HiDPI for macOS; they recommend 5K@27" or 6K@32". Others say 4K@27"/32" is fine on Windows or Linux with 150%/fractional scaling.

Tools, workarounds, and limitations

  • BetterDisplay is widely praised, but several confirm it can no longer force full 4K HiDPI on M5.
  • Some mention alternative tools (e.g., screenresolution) but note they don’t control scaling/HiDPI behavior.
  • Complex setups (PBP/PIP ultrawides, multiple cables, virtual displays) are used to regain acceptable text rendering, often with significant effort.

Technical hypotheses

  • Thread cites parsed driver/firmware structures showing per-“sub-pipe” max source widths (e.g., 6720 vs 7680) and architectural changes from M2 to M4/M5.
  • Speculation includes scaler clock limits, memory bandwidth/cache constraints, and conservative DCP firmware allocation.
  • Some think it’s a hardware/architecture choice; others suspect firmware/software policy that could be revised.

Meta: article quality and Apple response

  • Multiple commenters say the blog post appears partially LLM-generated and internally inconsistent, making diagnosis harder.
  • Suggested effective path: file concise, evidence-based bugs about “poor text on LoDPI displays,” include photographic comparisons, and/or escalate via Apple CEO email.
  • Broader frustration surfaces about Apple’s neglect of third-party displays, past DisplayPort/refresh-rate regressions, and removal of subpixel antialiasing.