In designing a port for Undertale, a number of changes were made to fill in gaps for lack of physical button input. Despite being available for platforms that do have touch capability, no version of Undertale makes use of device touch capability.

One of the most frequent changes made to the game’s user interface in this port was increasing the space allocated for on screen objects because of both small screen size, and the need for touch control.

Game menus, usually tight and compact because of button selection, were expanded and made larger to accommodate for smaller screen size, as well as touch functionality.

Given the size of contemporary smartphones, and the fact that players wouldn’t be using buttons to select menu items, the margins between menu items were increased. This allowed for more space between items, reducing the possibility of players mis-tapping the wrong item. Menu items were also given a border, increasing the touch target size for each menu item and allowing items to be clicked on their right side and much of their text to still be seen while tapping. Since Undertale’s overworld is paused when the menu is active, the menu size was increased to afford this additional space.

Previously, due to the nature of button selection, a menu item is highlighted at all times (fig. 1 in the left image this is indicated by the grey “ITEM” text and the heart next to the “Say Hello” item in the submenu). This isn’t the case with touch controls as players don’t always have their fingers on screen; because of this, the heart icon was removed. Now, selected items like the “CELL” menu in the image on the right, are highlighted in yellow.

In Undertale for platforms like PS4, Xbox One, Nintendo Switch and Playstation Vita, because of the ratio of the screens they’re played on in comparison to the game’s display area ratio, the game often has large black bars on the left and right side of the display area (highlighted in red below). In the game’s settings, this can been remedied with patterned frames, but the display area remains the same ratio.

In Undertale for Android, The game’s display area is stretched to fill more of the screen creating smaller black bars and utilizing more of the device’s screen as playable area. Again, this was done to make it easier for players to select exactly where they want to move their character and select which object in the world they wish to select, aiming to reduce mis-taps.

The bullet board is where much of the game’s challenge takes place and is a mostly static, but sometimes dynamic and moving play area dependent on the opponent and their abilities.

Again, to accommodate for Undertale for Android’s port to a typically smaller screen size, and now tap and drag control of the character’s SOUL, more space was created for movement as the player must now navigate their soul around the bullet board with their finger as opposed to fine button or joystick controls. On top of this they also must do so while likely covering their view of their SOUL with their finger. The expansion of the bullet board was done to balance the challenge added by adapting to the touch interface. To do so, the opponent’s character sprite was moved higher on the screen, and the aesthetic background patterns disappear while attacking, returning after the bullet hell period.

While rotating the screen to portrait orientation for bullet hell segments was considered to create more space, this was thought to be too tedious to ask players to do repeatedly and may cause issues with players’ screen orientation settings.

With no button input available via joystick or directional keys, Undertale for Android uses a destination tap or drag system of movement. Reminiscent of games like Animal Crossing: Pocket Camp, players can tap the location they’d like their character to move to, and the game will respond by moving character there after the tap, taking the straightest path possible. If players place their finger on a location on the map and drag it in a particular direction, the character will follow to the tap location, and continue to follow if the character proceeds to continue dragging their finger.

This was considered a viable solution because while Undertale’s bullet board segments require fine control of placement, they are very few places in the game’s overworld that require very fine control over player location where this system is not appropriate. The situations that do (e.g. the Undyne chase segments), require user testing and evaluation.

The Bullet Board mechanic will make use of a similar system of movement, where players must first place and hold their finger on their SOUL before the bullet hell projectiles start, and drag their finger around the board area to avoid projectiles. Should they release their finger over the SOUL icon, it will remain in place.

With no buttons, therefore no dedicated menu button, players navigating the overworld must select the menu button from the top right corner of overworld screens to open the game menu and make selections. Tapping off of the menu or submenu closes the corresponding menu.