Hermes 1.3 API: Palette Handling

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## 2. Palette Handling

If you want to use 8 bit indexed modes, you will have to use palettes. Also, if you want to use indexed modes, you will have to tell HERMES what palette you are using so it can create lookup tables, and so on.

HERMES needs lookup tables in order to convert efficiently from 8 bit to other formats without worrying you. If you just make a few function calls, HERMES will make sure your 8 bit mode works on any other mode.

As a last remark, palettes are stored as 8 bit per colour component values, NOT 6 bit. Keep it in mind.

## 2.1 HermesHandle Hermes_PaletteInstance()

This function returns a handle for you to use in subsequent palette handling operations. It will return zero on failure. Store this handle somewhere, you will need it for the following functions. This has to be the first function to be called before any palette handling.

## 2.2 void Hermes_PaletteReturn(HermesHandle handle)

If you are finished, use this to return your palette. This will free up the memory occupied by the palette and all the cached tables, etc. If you pass an invalid handle, your call will be ignored.

## 2.3 void Hermes_PaletteSet(HermesHandle handle,int32 *palette)

Surely, if you have a palette, you might want to set it. Use this function to copy 256 4-byte values from the pointer provided into the internal HERMES palette specified by handle. It would be a wise thing not to use this at all, i.e. not to store your own palette, but use the one already in HERMES, otherwise you are storing everything twice. In this case, look at the next function that says how to get access to the internal palette. But read on for caveats.

If you call this function, HERMES will assume that your palette has changed and flag all it's lookup tables invalid. So do NOT call it in a loop or anything unless your palette really does change. Lookup table recreation does not take place in there, however, but only when you actually convert something.

CAVEAT: This is the only function that invalidates the lookup tables of HERMES. If you use the next function, Hermes_PaletteGet, to get a pointer and then modify the palette, HERMES will not know that it has changed. Thus, any conversion to a non-indexed mode will draw garbage. You can use the Hermes_PaletteInvalidateCache in this case to force regeneration of lookup tables upon the next conversion.

## 2.4 int32* Hermes_PaletteGet(HermesHandle handle)

As said up there somewhere, it is probably wiser to let HERMES store the palette you want to use as it has to do it anyway. You can use this function to get a pointer to a 256-integer array of colour values.

Feel free to modify the palette, but keep in mind what is written above, you will trick HERMES and its lookup tables will be invalid. Call the next function documented below to resolve this.

Also, HERMES will return 0 if you pass an invalid handle. Take care of this as it will probably cause you a segmentation fault.

## 2.5 void Hermes_PaletteInvalidateCache(HermesHandle handle)

As described above, this function will cause HERMES to mark invalid all its lookup tables. As a consequence, when the next conversion from 8 bit is done, one of them will have to be regenerated. (By the way, 'regenerate a lookup table' sounds like pulling your teeth out. It is not. It's a minor thing, just a 256 byte table, no need to worry)

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