Scale a UV mapping to fit a exact rectangle

Question

Because I'm making tileable mesh, I have to resort to some programming hack in order to automatically generate missing textures for having them tileable without to adding too much pressure on my artist (later he can repaint some junction pieces if he want, but I'm pretty sure the image blending algorithm will be fine for the 95% of the cases).

However to do that I need to place UV coordinates with pixel perfect precision.

Here's actually my 3D model:

If you look carefully to the above picture you will see that the UV mapping is not fitting exactly in 1/4 of the original texture.

I want to align the UV mapping to have extreme corners at a texture corner and at texture center (basically => fit inside 1/4 of the final texture)

Most UV vertices need to be placed manually snapping to 1/64 increments. (think to the texture as a chessboard with 64 cells on each side: there are 64+1 possible coordinates on each dimension). That's also because some UV maps are deformed by Blender, so I cannot just "scale" those to fit in exact areas.

I need either to know:

• How to enter manually UV coordinates in UV/Image editor
• Or how to snap UV coordinates to 1/64 or 1/32 grid.

Answer 1

You may select the desired vertex of the uv island, press G, then X (or Y depending on what axis you want it to transform) and type the value using keyboard. You can also enable the Snap during transform (Increment) option to snap the vertex to the grid in the Uv Editor (hold Shift to snap by smaller distances).

You can also use the vertex coordinates buttons in the UV Vertex panel of the UV Editor's properties shelf (N).

You can edit your UV island's appearance using the same tools as in 3d view window. To make the edge perfectly horizontal or vertical select the vertex you want the other ones to allign to and press Shift+S-->Cursor to Selected. Next (with the pivot type set to 2D Cursor) select the vertices to allign and scale it by 0 along X or Y axes (S,X (or Y),0).