Games Find dominant colours in a game graphic

I have objects in my game that explode into coloured shrapnel. It would be nice if the colours of the shrapnel match the colours of the sprite, e.g. a mostly green object would explode into mostly green pieces.

Any suggestions on how to implement this? There are libraries such as ColourThief that extract the dominant colours from a bitmap, but how do I get the bitmap for a game object? I could presumably use BodyWrapper.GraphicName to find the name of the graphic and GraphicCache.GetGraphic to get that graphic as a CompressedBC. But how do I then turn a CompressedBC into a B4XBitmap?

There are quite a variety of objects so manually setting up a colour palette for each type fo exploding object would be tedious.

Choose random pixels from the game object (sprite?) until you've got say 10 samples with say alpha >50%. Or for something more deterministic, choose 20 random samples and sort them by alpha and use the "best" 10.

If that still sounds slow: precalculate it beforehand, so you have a ready-to-go array of say 10 explosive colours for each game object (sprite?).

Or can you slice up the sprite bitmap say 6 x 6 so that you have 36 pieces of shrapnel? Although they'd look odd being rectangular, so maybe try setting alpha of edge pixels to random 0..50% to give jagged edges?

Or are your explosions like mini sprite-sized 2-second movies, rather than individual pieces of shrapnel? And you want to change the movie's colour to make it more like the color of whatever it is exploding?

emexes said:

Choose random pixels from the game object (sprite?) until you've got say 10 samples with say alpha >50%. Or for something more deterministic, choose 20 random samples and sort them by alpha and use the "best" 10.

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That's the kind of thing I want to do, the question is, how to I actually get pixel colour values from the sprite?

If I had an ordinary bitmap object it would be straightforward, but the sprite comes in the form of a CompressedBC and I'm not sure how to work with that. (I can find documentation on how to convert a bitmap into a CompressedBC but not vice versa.)

I don't mind if the process is slow - as you say, I can precalculate beforehand if needed.

Andrew Gray said:

Any suggestions on how to implement this?

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I would use ColourThief (or something like it) to preprocess all graphics and get a short list of their dominant colours. That would eliminate the need to do it live.