Depth: paper, front and back

How a flat picture becomes a solid, and the few decisions behind it. For the steps, see Make a 3D model.

A column per pixel

Rise gives every fully opaque pixel a column of voxels (cubes). The column has three parts:

• Paper: the one voxel the pixel always has. A picture you never touch is paper everywhere, one voxel thick, a card cut to the shape of your art.
• Front: how many extra voxels stand out toward the viewer.
• Back: how many extra voxels reach away from the viewer.

So a pixel with front 2 and back 1 is 1 + 2 + 1 = 4 voxels thick. Front and back are each one byte (0 to 255) per pixel, which is why the stored depth map is exactly two bytes per pixel; see File formats.

The model is the art, extruded. Its texture is one image with the front picture on the left and the back picture on the right, a one-pixel gutter between them so a sample exactly on the front half's right edge (models sample with NEAREST, and float rounding can land on the edge) never reads the back half. The sides of every column take the color of the art's edge pixel there, so a column whose edge pixel is near black gets a near-black side. That is how it is drawn, not a bug; give the edge a lighter outline if you want lighter sides. Where two layers own a column's front and back, its side changes from the back owner's color to the front owner's at the seam. A layer under the top one is colored with its own rolled color, so the back shows the right layer's color.

Sets cooked before this stacking rule keep the models they were cooked with; cook again to get the new ones.

"Depth" means two things here

The Explorer's depth is a layer's position in the stack: depth 1 paints first and sits furthest back. That is paint order, and it decides which layer hides which. The Rise page's depth is thickness, how far a pixel stands out of or sinks behind its own plane. The two meet only when a Recipe is risen: the stack is flattened to one picture by paint order, and each visible pixel takes the thickness of the whole stack there: the front reaches as far as any solid layer's front, the back as far as any layer's back, and each face takes the color of the layer that owns it. A layer on top can add relief but never cut away what a layer under it built.

One solid, from finished art

A model is built from one finished image, never from layers. A Recipe's roll is composited first, exactly as cooking composites it, and the single result rises. So a model always matches the picture you would have shipped.

A voxel is there or it is not

Rise asks one question of every pixel: is it fully opaque? Yes means a column. Anything else, fully clear or partly transparent, is not solid.

Fully clear is fine: nothing is there. Partly transparent is the difficulty. A 40%-opaque pixel has no correct voxel: a cube is 100% there, and any rule that turns the pixel solid or empty throws away something you drew. nfty will not choose for you silently, so a picture with a partly transparent pixel is refused, naming it. For a stack, the check runs on every layer before compositing, so a partial pixel cannot hide beneath an opaque one.

Why 2D only is derived

A book, Recipe or Ingredient is 2D only when any of its art has a partly transparent pixel. That is a fact about the pixels, so nfty never keeps it as a setting you could get wrong. The partialAlpha flag in each manifest is a listing cache: every writer recomputes it from the pixels, and every reader that decodes pixels recomputes it again. A hand-edited flag cannot make a soft-edged book look voxel-ready, and a fixed book cannot stay marked.

The cost of deriving is a pixel scan per Ingredient each time the tree rebuilds, which is why the mark appears after a save rather than on every keystroke.

Partial alpha stays legal for everything else. Images, metadata and rarity do not care; only models do. That is why the padlock that keeps painting opaque can be turned off, with a warning, rather than removed.

Why "make voxel-ready" is a tool, not a default

Snapping partly transparent pixels to solid or clear (at 50% alpha) is a decision about your art, so it happens only when you ask, shows you every variant it will change, and can be undone. The alternative, rounding on export, would produce a model that differs from the picture in your collection without ever saying so. Compare Why nfty never resizes your art.

Why the debug mark never reaches a model

Cooking can stamp each asset's number in a corner, for checking a sheet by eye. That is a property of an exported image, applied on the way out to a copy. A model is copied as cooked, and its texture is the unstamped asset, so a mark can never end up painted on a 3D model. The export card says so beside the mark option.

Why a gray layer rises gray

A Dynamic or Static layer is stored as a gray value-map, and its color is decided when an asset is cooked (Why layers are drawn in gray). Risen from the Rise page, such a variant is therefore its gray pixels, exactly like a loose picture of them. A model of a cooked asset carries the colors that asset rolled, because cooking has colored it by then.