Scrolling Game Development Kit UI Help Up to Edit Maps Dialog

Special Functions

This is part of a series of pages describing the Edit Maps Dialog. This page describes the Special Functions tab.

In order to edit special functions you must have a map selected and the player sprite must have been specified. This is required because some aspects of a special function require the layer in which the player sprite resides.

Along the left side of this tab are listed the special functions defined on the selected map. This is the top level of navigation within this tab. Selecting one of these special functions loads the information for the function into the sub-tabs at the right.

Note: In version 1.1 and earlier, only functions on the player sprite's layer were listed here because the only way to activate a function was for the player (on the same layer) to touch it. The problem with this is that there was no way to edit or delete functions that may have accidentally been added to other layers. Furthermore, there is now the ability to activate any special function(s) when the game begins. So for multiple reasons, all special functions on the selected map are now listed. Functions that reside on a layer other than the player's layer are discernible by the fact that the "Action Parameters" tab hides the controls relavent to the player when such a function is selected.

Action Parameters

The first sub-tab restricts when the special function will take effect and whether it can be activated again. The following options exist on this tab.

And there are a number of options specifically geared towards correlating the input device with activation of the function. Most of these are new with version 1.4 (everything except Up, Button 1 and Down).

Notice that if the the "All at once" box is not checked, any one of the checked buttons can be pressed to activate the function.


This tab has a lot of content to support the various types of special functions that are defined in GameDev. The "Function" field at the top of this tab determines what the selected special function should do when it is activated. The information presented below the function field is specific to the selected function.

Display a Message

This type of function pops up a box that displays a message or image and waits for the player to press a button. The game freezes until the message is acknowledged. To display an image enter "#PIC" as the first 4 characters of the message and then enter the path and filename of a bitmap to display. A space following "#PIC" is optional, however there must be no spaces before or inside the text "#PIC" itself. The path should be relative to the path of the GDP file for the project. The image will display centered on the screen and act just like a message until the player presses a button.

This function has been greatly enhanced in version 1.3 and you can now set the font name, size, color and style using #FNA, #FSZ, #FCL and #FFL respectively. Each code must go on a line of its own like the #PIC code. Furthermore you can now display text on top of the picture by adding text starting on the line after the codes. The picture size will be used to determine the size of the rectangle in which the text is printed. I recommend you use the new Message Wizard button to compose your messages now instead of typing these codes in, to make this process easy.

This dialog is displayed when you click the "..." button next to the text box for the message. Here you can separately enter all your parameters for the message and the proper code will be entered for you in the message box for the function. Note that you can leave the text box blank in order to simply display a picture, or leave the image field empty if you don't want a background image for your message. In case you should need to know, the codes are formatted like this (each code goes on a line by itself followed by it's parameter. A space is optional):

Switch to a New Sprite

This changes the player sprite to a new sprite. This could come in handy for changing the appearance or functionality of the player, or switching it to an automatically controlled sprite for a period of time while it travels from one point to another. The new sprite will continue to interact with the map as the player sprite always does. There are a few options associated with this function:

Switch to a New Map

There would be little point in having multiple maps within a project if the player were not able to jump between them. This function will transport the player to another map. Usually, the current map is unloaded and the new map is initialized (default instances of sprites are created where appropriate). Then you have the option of starting the player in the default location for this map or overriding the player start position and/or sprite with one of your own choosing. Selecting "(default)" from the "As this sprite" box uses the sprite specified as the Player sprite for the map. The definition you select must be a sprite that has "Initial Instance" checked and would be automatically created when the map is initialized. If you want to override the starting position instead of using the default position for the sprite, you may check the "Set start position" box and specify an X and Y coordinate in pixels. This coordinate is given as an offset from the top left corner of the layer in which the sprite resides.

There are two new features here as of version 1.4. First, notice the "Remember Old Map" checkbox. This will store the location that the player was at before switcing to the new map so you can return to it later. Up to 5 locations can be remembered at a time. When returning to an old location, the last one stored is always used. This is ideal for switching to a menu screen or some other globally accessible location because it's easy then to switch back to the remembered location no matter what map the player was on when they switched to the new map. Next notice the "<Return to old map>" selection in the map list. This is the counterpart which implements the other half of this feature. After storing a location, you return to it by having another function that switches back to the old map. The other feature is the ability to switch to a map without restarting the sprites. The "Restart Sprites" checkbox is checked by default, but if you un-check this box, then whenever you return to this map, it will remember what sprites were there when the player last left that map. If an existing player sprite cannot be found on the map, the sprites will be re-initialized regardless of the state of this option (for instance, if this is the player's first visit to the map).

When the player switches to a new map, the inventory is retained. There may be different interactions defined on the map, but all maps are defined in terms of the same inventory. This is the reason for separating the inventory's interaction with the map (on the Player Interaction tab) from the inventory definition itself (on the Player Settings dialog).

Teleport to a Location

The player can be teleported either to an absolute position or to a position offset from the player's current position or from the trigger point. Coordinates are given in pixels. For an absolute teleport (if the "Offset" boxes are left unchecked) coordinates are given in pixels from the top left corner of the layer in which the player resides, and a preview of the destination location is displayed at the right. The coordinates specify where the top left corner of the sprite should end up. If the "Offset from current" option is checked, the teleport will be an offset from the player's current position. If "Offset from trigger" is checked, the teleport will be relative to the trigger point. The trigger point is set to the location of the last sprite collision, sprite path ending, tile interaction or function activation by the player itself. ("sprite path ending" refers to a sprite that triggers a special function when it reaches the end of its path.)

Alter Map

This is a particularly useful function for changing a piece of the map. It copies the tiles from under another special function and puts them wherever you want. Everything must occur on the same layer as the player. It's not possible to copy tiles accross layers, or to copy areas of tiles from one place to another on a layer other than the layer where the special function was triggered. All the tiles will be copied from under the specified special function to the location specified. The location specified indicates the top left corner of where the tiles are output.

As of version 1.4, the new option "Relative to tile behind trigger point" is avilable. The trigger point is set in pixels, but this function can find the tile that contains the trigger point coordinate and use that as a tile location to set the target location of the copy. This allows, for instance, an easy way to turn a sprite into a tile when it reaches the end of its path and triggers this kind of function.

The "Pick cordinates" box is not part of the special function, but rather a tool you can use to calculate coordinates. If the function being defined happens to contain the destination rectangle (aligned to one corner) you can use the Pick coordinates box to enter the coordinates necessary to copy the rectangle to the appropriate corner. For instance you may have an "UnBlockPassage" function defined at 24,20 to 26,23 and you have an "OpenedPassage" function defined at 100,50 to 101,53 (notice the open passage is one tile narrower horizontally). "UnBlockPassage" represents the area the player can touch to activate a function that copies an image of an opened passageway into the tiles at 25,20 to 26,23. "OpenedPassage" represents this image being copied. Since 26,23 (the bottom right corner) happens to be the same for "UnBlockPassage" and for the rectangle you want to affect, you can select "Match bottom-rights" from the "Pick coordinates list" and it will enter the coordinates "25,20" for you (the top left corner of where the copy must begin to make the bottom right corners match). This tool is convenient if you don't know the coordinates of the destinaton, but you know the destination matches a corner of the function you're currently defining.

Create Sprite

Use this function to create a new instance of a sprite based on the specified sprite definition. You can override the default start position for the sprite if you like by checking the "Set start position" box and entering a pixel coordinate. If the "Absolute" option is selected, the coordinate will be interpreted as pixels relative to the top left corner of the layer. If "Relative to player" is selected, the coordinate will be added to the position of the player. The top left corner of the new sprite will start at the specified offset from the top left corner of the player sprite. If "Relative to trigger" is selected, the sprite will start at the specified offset from the trigger point (new as of version 1.4). The trigger offset feature is good for things like creating explosion effects at the location of a collision between two non-player sprites. The "Maximum count" parameter sets a maximum on how many of the sprite the function should allow. The function will not create another instance of the sprite if the maximum number already exist. (The last parameter is new with version 1.2.)

Raise an Event

This function does not require any parameters. Instead all the work in this case is handled in script. This is a particularly useful option as it allows you to do anything you want if the other function types do not cover the effect you want the special function to have. The Player object's "OnSpecialFunction" event is raised when the function is triggered, and the "SpecialFunction" object that was triggered is passed to the script code as a parameter.

As of version 1.3, any function can raise an event by checking the appropriate box in the "Action Parameters" tab. The purpose of this function type, then, is when there's nothing else you want to do besides raise an event.

Delete Sprites

To prevent the map from becoming over-populated with sprites you may want to make frequent use of this function. It allows you to delete one or all instances of sprites based on the specified sprite definition. Specifying a minimum will prevent all sprites from being deleted by the function; the function will only delete sprites if the minimum number will still exist. Specifying a minumum and checking the "Delete all above min." box will delete sprites until the specified number of sprites exist for that type of sprite. If the minimum is set to zero and the box is checked, all sprites of the specified type will be deleted at once.

Alter Inventory

The Action Parameters tab allows some simplistic manipulating of the inventory, but this only allows subtracting from the inventory and only takes effect when the function is activated by the player touching it. This Alter Inventory function allows you to do more. You may specify any item in the Item name field. You can also enter positive or negative values in the "Change by" field. Positive values will add the specified item to the inventory while negative values will subtract. You can also specify what happens if the inventory item reaches its max (if adding) or 0 (if subtracting) by choosing another function from the "If limit is hit, activate" field. This allows you to activate a special function if the player reaches an upper or lower limit on a particular item. You can also choose to automatically reset the count to the opposite limit when this occurs. One example of using these would be health and life count. A special function can be used to reduce health. When health reaches 0 you can automatically activate another function that reduces life count by 1 and check the box to have the health reset to full. The function that decreases life count could in turn activate another function to teleport you to an end game map if the life count reaches 0. This kind of function would probably be activated often from sprite collision definitions.

Activate Series of Special Functions

OK, so you don't want to write script. Besides, it's cool to show how much GameDev can do without resorting to script. So here's the answer. This may become the most powerful special function yet. It allows you to combine a number of other special functions into one so you can activate them all at once in any order any number of times. Simply select the function or functions that you want to execute in the lefthand list and click the ">" button. These functions will then be added to the list for this function. You can sequence the list however you like by selecting functions in the righthand list and clicking the up and down arrow buttons. The same function can be executed multiple times too, if necessary. And so long as you don't end up with any circular references, you can even have one series call another series. If you need to remove anything from the righthand list, click the "<" button.

Save / Load Game

This function (new as of version 1.4) performs a few different operations with save game files. Saves are represented in GameDev with a slot concept. The names and quantity of the "slots" are determined by the "Game name" values specified for save game functions by the game designer. The specific function is selected by picking one of the options on the left:

Buttons at the Bottom

There are 5 buttons along the bottom of the Special Functions dialog: