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I wanted to use flowmap texture for direction / rotation of instances generated by geometry nodes.

I saw quite nice explanation of basics behind, but ... it says in one part - pure Green channel goes in up (Y) direction and later under color grid the same color is pointing to up-left direction. What I'm missing here?

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Another story is ... When I tried to apply this grid texture to orient instances under GN it takes Red in X dir, Green in Y dir ... and completely ignores negative (dark) direction as shown in the grid texture.

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What I'm missing in my node tree?

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Basically I wanted to use awesome addon Flowmap Painter (of Clemens Beute) to paint texture let instances orient in a brush movement ...

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Edit

Provided solution in answer works great ... Thank you guys :)

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    $\begingroup$ A color value is always positive, so you would have to map it to a range from $-1$ to $1$. $\endgroup$
    – quellenform ♦
    Commented Aug 31, 2022 at 9:33

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Even if @Crantisz was once again faster, here nevertheless my answer to it, because here also the directions are treated correctly:

enter image description here

Note that the colors play an essential role here, as already discussed in this question:
Colour/color space option for image textures in geometry nodes

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  • $\begingroup$ Thanks a lot :) Will test it more ... $\endgroup$
    – vklidu
    Commented Sep 1, 2022 at 6:27
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    $\begingroup$ I had an issue with flowmap painter wrong orientation, than I noticed my grid texture in sample blend file (I took from net) was flipped on X compare to standard UV coordinates (like black at bottom-right should be at bottom-left). So I edit my picture and switched Map Range value for Red channel at your image. Anyway works nicely imgur.com/KnLZKJB ... I have also issue with using on sphere object, so probably I will ask for additional help later :) $\endgroup$
    – vklidu
    Commented Sep 1, 2022 at 19:26
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There are a lot of issues here. First one, we need to tell Blender that we need non-color data. So that open your image in shader editor and change color space to Non-color or linear

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Next, as quellenform sad, you need to change the range of colors from 0...1 to -1...0, Or subtract 0.5

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You should also make a Z-component based on the length of X+Y components

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  • $\begingroup$ Thank you, I appreciate your help. $\endgroup$
    – vklidu
    Commented Sep 1, 2022 at 6:30
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    $\begingroup$ Pedantic: I think you meant "...to -1...+1"? $\endgroup$
    – Matthew
    Commented Sep 2, 2022 at 0:36
  • $\begingroup$ Your node tree works for me for texture grid orientated with black bottom-left (that I flipped later). I skipped Z since it twisted instances a bit imgur.com/rXLGfLu ... what I can't figure out why bottom row (red) is slightly shifted down (and not 45 deg as quellenform's) imgur.com/FLgcB6N for uflowmap seems to be identical (or less noticeable?) $\endgroup$
    – vklidu
    Commented Sep 2, 2022 at 7:35

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