Colour overlays

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Feature proposal.png This article covers a feature proposal.

Feature proposals are suggestions what kind of features the PARPG engine should support. Feature proposals are used as basis for code proposals, which describe how to implement the proposed features.


Colour overlay

A colour overlay is a separate image file that lies on top of the base sprite and provides additional colour information about it. Each individual sprite has its own colour overlay for each frame of animation. Each overlay could in theory contain as many channels as there are colours, but I would dare say that in practice it will be highly unlikely you will need more than 4 channels per overlay. The standard four colours and their corresponding channels I propose are:

  • red - primary colour channel
  • green - secondary colour channel
  • blue - terciary colour channel
  • black - neutral channel, no colour change

In Fallout it was possible to re-colour critters (and other objects?), but there was no way to re-colour only certain parts of the sprite. By using overlays, you get a lot more control over colouring the base sprite.

The 1st image is the base sprite, the 2nd one is the colour overlay and the 3rd one shows a few of the many possible colour combinations. Black means no colour change so those parts are left grey, or whatever colour these parts are on the base sprite. By using only two image files you get toilets galore, for no additional work or increased file size.
By using multiple overlays per base sprite you can quickly get various results with a single base sprite. Red and green channels in the top-right result have the same colour applied.

Other characteristics of a colour overlay

  • it should be completely optional, so the game developers choose whether it benefits their needs or not
  • areas of the base sprite that are influenced by the overlay should be in greyscale, everything else can be of any colour
  • option to change colour of the primary, secondary and terciary colour channel while the game is running. This would be done by the player using either a set of given colours or using a colour picker to choose any possible colour. It should be possible to change colours for all parts of the critter at once (shield, body, cape, etc.)
  • option to lock specified colour channels, so they cannot be edited by the player while the game is running
  • one base sprite should have one or more different overlays to choose from, but only one overlay should be in use at any given time. It should also be possible to change what overlay is in use while the game is running. This would allow the players to choose from different colour distributions over the sprite. For example, the player could pick what pattern/insignia he wants to have on his shield or armour.
  • it should be possible to change different overlays for multiple parts of the critter at once. For example if the player wanted to change his insignia from cross to chess pattern, all of the critter parts would change from cross to chess pattern, this includes, capes, shields, armour etc.

Benefits of colour overlays

  • Reduced number of needed base sprites
  • increased flexibility and customization
  • Since a colour overlay has a limited amount of different colours (usually only 4), it doesn't take much disk space, especially when the image is compressed
  • they are easy to make, the artist must simply apply red, blue, green and black shadeless materials to apropriate parts of the 3d model, turn of antialiasing and re-render the sprite


  • An overlay has no antialiasing so borders between different colours are rather sharp. However, if the sprites are not too big, this problem is not so obvious

Is it possible to have antialiasing in colour overlays?

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