hi,

in fact it's a GX restriction, since your texture is divided in a matrix of 2x2 textel  to be displayed/maped you will need a mul of 4

now you can easily forget about this restriction since you just have to add missing lines or row (to get a mul of 4) using a full transparent color using your fav drawing software (gimp is really easy to handle this things)

ie you can have a texture of only one pixel (create a full transparent 4x4 png, and draw your pixel on the top left corner)

if you need more info, just ask

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