Here you'll find descriptions for certain options that require extra explanation
Common options (in most ports) organized by section:
Display Color Format: Color depth of the app's final output framebuffer
Render Color Format: Color depth of the emulated system's framebuffer
Effect Color Format: Color depth of any intermediate shader effects
Buffer Size In Frames: Set the approximate amount of video frames worth of audio to buffer. Lower values reduce audio latency but increase the chance of audio skipping when frames drop. Not all devices can reliably handle low buffer sizes so you may need to experiment with different values.
On-screen Controls: turn touch screen controls on/off, or automatically if an alternate input device is present (slide-out keyboard, Wiimote, etc.)
On-screen Config: fine-tune virtual controls, a preview image is shown in the background
Blend Amount: control translucency, a higher percentage makes the controls more solid (not shown in the preview)
Button Size: physical size of a single face button (A, B, etc.) which is also used to calculate the size of other elements via a multiplier
Open Menu: position of shortcut command to open the app menu (this element is invisible)
Fast-forward: position of shortcut command to toggle fast forward on/off (this element is invisible)
Button Spacing: physical size of the gap between the face buttons. Increasing spacing makes it easier to push 2 buttons at once with your thumb since the gap area contains a bounding box that triggers both buttons.
Button Stagger: horizontal/vertical multipliers used when arranging face buttons. A value of 0 arranges buttons in an even grid while 1 gives a diamond shape similar to a SNES controller.
H & V Overlap: extends the horizontal/vertical bounding box for face buttons by (Button Spacing + Button Size * Overlap), "Gap-only" adds just Button Spacing.
Show Bounding Boxes: shows exact screen areas used for detecting input, the d-pad is color coded: white = single direction, green = diagonal, red = deadzone
Background Bluetooth: Keep Bluetooth connections active even when the app is in the background
Bluetooth Scan Cache: Use results from previous scans to speed up future ones. Try temporarily turning this off if you have issues during Bluetooth scans.
Auto-save state: Save a state to the "a" state slot when the game is closed, or the app backgrounds/exits.
Alt Gamepad Confirm: When using a game controller, swap the confirm/cancel buttons in menus
Title Bar Back Navigation: Places a back shortcut icon in the top left of the title bar
Remember Last Menu: When opening the menu from a game, goes to the last recently used menu instead of the main menu
Suspended App Icon: [Android only] Leave a shortcut icon in the notification bar if the app goes into the background
Dim OS Navigation: [Android 4.0+ only] Dims the navigation bar (aka "Lights Out Mode") upon app start or loading a game
Hide OS Navigation: [Android 4.0+ only] Hides the navigation bar on devices that allow it. Note that it will return automatically if the screen is touched due to OS restrictions. Only useful if you have some key-based input.
Input Device Setup:
This menu includes configuration settings for key-based input devices supported by the app & OS (Android HID gamepad/keyboard devices, In-app Wiimotes, etc.).
On-screen Input Player: The player represented by the on-screen controls
Delete Saved Device Settings: Deletes any per-device data stored in the config file. This includes anything you've changed in the device's sub-menu except for the custom key profiles
Auto-detect Device To Setup: Lets you quickly jump to an input device's sub-menu by pushing any key on it
[Device Names]: This is a list at the bottom of the menu showing all input devices available, selecting a device goes to its specific sub-menu with the following options
Player: The player the device represents. To use one device with multiple players, such as two people playing on a single keyboard, select "Multiple" to reveal additional key categories.
Profile: Select from one of the built-in or custom key profiles
Set [name of key category]: Assign keys to various in-game actions and emulated inputs for the current profile. Profiles are shared between devices so if you have 2 of the same controller, you only need to assign the keys once and switch the player/profile option in the 2nd controller's menu. If you have a controller that's split into multiple devices by the OS (ex. some Android gaming handhelds where the d-pad & buttons are 2 separate devices), use a single custom profile for both devices to keep their keys linked together.
iCade Mode: If the device uses the iCade protocol as listed on the device documentation, enable this to recognize input from it