Hi i woul like to paint my logo on a weighmap for my grass system but i cant figure out how to change the brush or use a texture like in texture paint mode. Is it nor possible? Should i draw the logo on hand?
To transfer a texture to vertex weights, you can use a Vertex Weight Edit Modifier, which accepts a texture as a mask.
Personally, I find the current documentation unhelpful, and I haven't managed to reverse-engineer the logic of the modifier's fields from its behavior, so this answer isn't as complete as it should be.
The 'Logo Tex' texture in this example is a white out of black logo. The 'Logo Group' vertex group is all the vertices of a subdivided plane, set to 0, initially.
The critical settings for this case appear to be a smooth or spherical falloff, and a value in the Add Threshold slightly above the Default Weight.
You can apply the modifier and take the result into Weight Paint to smooth, or make other alterations to it.
It would be great if in a comment or proper answer to this question, someone could explain exactly what the settings are doing, or point me in the direction of a tutorial that isn't actually about something else, or based on guesswork.