Update Geargrafx docs

Author: drhelius

docs/library/geargrafx.md

@@ -4,7 +4,7 @@
 
 Geargrafx is an open source, cross-platform, PC Engine / TurboGrafx-16 / SuperGrafx emulator written in C++.
 
-- Accurate emulation supporting the entire HuCard PCE / SGX catalog.
+- Very accurate emulation supporting the entire HuCard PCE / SGX catalog.
 - Support for CD-ROM², Super CD-ROM² and Arcade CD-ROM² systems.
 - Backup RAM and Memory Base 128 support.
 - Multi Tap support (up to 5 players).
@@ -173,8 +173,31 @@ Settings with (restart) means that core has to be closed for the new setting to
 
 - **No Sprite Limit** [geargrafx_no_sprite_limit] (**Disabled**|Enabled)
 
-    Enabling this option removes the per-line sprite limit, but may cause glitches in certain games.
-    It's best to keep this core option disabled.
+    Remove the per-line sprite limit. This reduces flickering but may cause glitches in certain games. It's best to keep this option disabled.
+
+- **Video Low-Pass Filter** [geargrafx_lowpass_filter] (**Disabled**|Enabled)
+
+    Enable a low-pass video filter to simulate the signal degradation of analog video output on CRT displays.
+
+- **Video LPF Intensity** [geargrafx_lowpass_intensity] (**100**|0 - 100)
+
+    Set the intensity of the video low-pass filter as a percentage from 0 to 100.
+
+- **Video LPF Cutoff** [geargrafx_lowpass_cutoff] (**5.0 MHz**|3.0 MHz|3.5 MHz|4.0 MHz|4.5 MHz|5.0 MHz|5.5 MHz|6.0 MHz|6.5 MHz|7.0 MHz)
+
+    Set the cutoff frequency of the video low-pass filter. Lower values produce a softer image.
+
+- **Video LPF HuC6270 5.36 MHz** [geargrafx_lowpass_speed_536] (**Disabled**|Enabled)
+
+    Apply the video low-pass filter when HuC6270 is running in 5.36 MHz dot clock mode (256px width).
+
+- **Video LPF HuC6270 7.16 MHz** [geargrafx_lowpass_speed_716] (**Enabled**|Disabled)
+
+    Apply the video low-pass filter when HuC6270 is running in 7.16 MHz dot clock mode (341px width).
+
+- **Video LPF HuC6270 10.8 MHz** [geargrafx_lowpass_speed_108] (**Enabled**|Disabled)
+
+    Apply the video low-pass filter when HuC6270 is running in 10.8 MHz dot clock mode (512px width).
 
 - **Backup RAM (restart)** [geargrafx_backup_ram] (**Enabled**|Disabled)
 
@@ -184,6 +207,10 @@ Settings with (restart) means that core has to be closed for the new setting to
 
 	When enabled, ensures deterministic emulation behavior for netplay by setting consistent reset values for memory and hardware registers. This helps prevent desyncs during netplay sessions.
 
+- **Safe VDC Defaults (Homebrew)** [geargrafx_safe_vdc_defaults] (**Disabled**|Enabled)
+
+	When enabled, sets safe default values for the VDC (Video Display Controller) registers. This can help some homebrew software run correctly.
+
 - **CD-ROM (restart)** [geargrafx_cdrom_type] (**Auto**|Standard|Super CD-ROM|Arcade CD-ROM)
 
     Select the CD-ROM system type. The *Auto* setting automatically selects the appropriate CD-ROM system based on the loaded content.
@@ -203,7 +230,7 @@ Settings with (restart) means that core has to be closed for the new setting to
 
 - **HuC6280A Audio Chip** [geargrafx_psg_huc6280a] (**Enabled**|Disabled)
 
-	Enable or disable the HuC6280A audio chip emulation. The HuC6280A provides the PSG (Programmable Sound Generator) functionality.
+	Enable the HuC6280A audio chip, as found in the SuperGrafx and CoreGrafx I. When disabled, the original HuC6280 chip from the PC Engine is used instead.
 
 - **PSG Volume** [geargrafx_psg_volume] (**100**|0 - 200)