kicad-zone-resistance/fill_resistance/raster.py

"""Rasterization of the fill polygons onto a shared multi-layer grid, and
electrode mask construction.

Grid convention: layer l, row i, col j maps to the cell center
    x = x0_nm + (j + 0.5) * h_nm
    y = y0_nm + (i + 0.5) * h_nm
in KiCad board coordinates (y grows down). Row 0 is the minimum-y row,
the TOP of the board as drawn in the editor; plots use origin='upper'.
All layers share the same frame, so cell (i, j) is vertically aligned
across layers (via links connect equal (i, j) on different layers).

Connectivity restriction lives in solver.py: it needs the via edges.
"""
from __future__ import annotations

import math
from dataclasses import dataclass

import numpy as np
from matplotlib.path import Path as MplPath
from PIL import Image, ImageDraw
from scipy import ndimage

from . import config
from .errors import ElectrodeError, GridSizeError
from .geometry import Electrode, Problem, Rect

# 4-connectivity: matches the in-plane 5-point stencil of the solver
_STRUCT4 = ndimage.generate_binary_structure(2, 1)


@dataclass
class RasterStack:
    masks: np.ndarray         # bool (L, ny, nx), True = copper
    x0_nm: float              # grid origin (outer corner of cell [., 0, 0])
    y0_nm: float
    h_nm: float
    layer_names: list[str]
    buildup: np.ndarray | None = None   # bool (L, ny, nx): solder buildup
                                        # (mask opening ∩ copper)
    chain: np.ndarray | None = None     # bool (L, ny, nx): cells that are
                                        # copper only through a 1D trace chain
    chain_edges: tuple | None = None    # (a, b, g_dc, layer) arrays: explicit
                                        # DC conductances of the chain links

    @property
    def nlayers(self) -> int:
        return self.masks.shape[0]

    @property
    def shape2d(self) -> tuple[int, int]:
        return self.masks.shape[1:]

    def cell_centers(self, i0: int, i1: int, j0: int, j1: int):
        xs = self.x0_nm + (np.arange(j0, j1) + 0.5) * self.h_nm
        ys = self.y0_nm + (np.arange(i0, i1) + 0.5) * self.h_nm
        return np.meshgrid(xs, ys)

    def cell_of(self, x_nm: float, y_nm: float) -> tuple[int, int] | None:
        """(i, j) of the cell containing the point, or None if outside."""
        ny, nx = self.shape2d
        j = math.floor((x_nm - self.x0_nm) / self.h_nm)
        i = math.floor((y_nm - self.y0_nm) / self.h_nm)
        if 0 <= i < ny and 0 <= j < nx:
            return i, j
        return None

    def extent_mm(self) -> tuple[float, float, float, float]:
        """imshow extent (left, right, bottom, top) for origin='upper',
        y axis in board orientation (increasing downward)."""
        ny, nx = self.shape2d
        return (
            self.x0_nm * 1e-6,
            (self.x0_nm + nx * self.h_nm) * 1e-6,
            (self.y0_nm + ny * self.h_nm) * 1e-6,
            self.y0_nm * 1e-6,
        )


def choose_cell_size(bbox_nm: tuple[int, int, int, int], nlayers: int) -> float:
    """Pick the cell size h [nm]; TARGET_CELLS counts TOTAL cells across
    all layers. Raise if the grid would exceed HARD_MAX_CELLS."""
    x0, y0, x1, y1 = bbox_nm
    w, ht = float(x1 - x0), float(y1 - y0)
    if w <= 0 or ht <= 0:
        raise GridSizeError("Copper geometry has a degenerate bounding box.")

    if config.CELL_UM_OVERRIDE is not None:
        if config.CELL_UM_OVERRIDE <= 0:
            raise GridSizeError(
                f"Cell size must be positive "
                f"(got {config.CELL_UM_OVERRIDE:g} um)."
            )
        h = config.CELL_UM_OVERRIDE * 1000.0
    else:
        h = math.sqrt(w * ht * nlayers / config.TARGET_CELLS)
        h = min(max(h, config.MIN_CELL_UM * 1000.0), config.MAX_CELL_UM * 1000.0)

    ncells = math.ceil(w / h) * math.ceil(ht / h) * nlayers
    if ncells > config.HARD_MAX_CELLS:
        raise GridSizeError(
            f"Grid would need ~{ncells / 1e6:.1f} M cells over {nlayers} "
            f"layer(s) at cell size {h / 1000:.0f} um (limit "
            f"{config.HARD_MAX_CELLS / 1e6:.0f} M). Raise MAX_CELL_UM / "
            f"CELL_UM_OVERRIDE in config.py, deselect layers, or measure a "
            f"smaller region."
        )
    return h


def _paint_ring(stack: RasterStack, ring: np.ndarray, value: bool,
                target: np.ndarray) -> None:
    """Set target (2D) cells whose center lies inside ring to `value`,
    working only within the ring's bbox. Hybrid rasterizer: PIL scanline
    fill for the bulk (fast, O(vertices + cells)), then the cells within
    a ~2 px band around the ring edge are re-tested exactly against the
    polygon, so the result is identical to a pure center-in-polygon pass."""
    ny, nx = stack.shape2d
    h = stack.h_nm
    j0 = max(0, int((ring[:, 0].min() - stack.x0_nm) / h) - 1)
    j1 = min(nx, int((ring[:, 0].max() - stack.x0_nm) / h) + 2)
    i0 = max(0, int((ring[:, 1].min() - stack.y0_nm) / h) - 1)
    i1 = min(ny, int((ring[:, 1].max() - stack.y0_nm) / h) + 2)
    if i0 >= i1 or j0 >= j1:
        return
    w, ht = j1 - j0, i1 - i0

    # cell (i, j) center <-> pixel (j - j0, i - i0)
    px = (ring[:, 0] - stack.x0_nm) / h - 0.5 - j0
    py = (ring[:, 1] - stack.y0_nm) / h - 0.5 - i0
    pts = list(zip(px.tolist(), py.tolist()))

    inside = np.zeros((ht, w), dtype=bool)
    band = np.ones((ht, w), dtype=bool)
    if len(pts) >= 3:
        fill_img = Image.new("1", (w, ht), 0)
        ImageDraw.Draw(fill_img).polygon(pts, fill=1)
        inside = np.array(fill_img, dtype=bool)
        band_img = Image.new("1", (w, ht), 0)
        ImageDraw.Draw(band_img).line(pts + pts[:1], fill=1, width=5,
                                      joint="curve")
        band = np.array(band_img, dtype=bool)

    bi, bj = np.nonzero(band)
    if len(bi):
        xs = stack.x0_nm + (bj + j0 + 0.5) * h
        ys = stack.y0_nm + (bi + i0 + 0.5) * h
        # Path(closed=True) treats the LAST vertex as the CLOSEPOLY dummy,
        # so the first vertex must be appended or the ring loses its last
        # corner
        verts = np.vstack([ring, ring[:1]])
        inside[bi, bj] = MplPath(verts, closed=True).contains_points(
            np.column_stack([xs, ys]))

    sub = target[i0:i1, j0:j1]
    sub[inside] = value


def rasterize_stack(problem: Problem, h_nm: float) -> RasterStack:
    """Rasterize every included layer onto one shared frame."""
    x0, y0, x1, y1 = problem.copper_bbox()
    m = config.MARGIN_CELLS
    nx = math.ceil((x1 - x0) / h_nm) + 2 * m
    ny = math.ceil((y1 - y0) / h_nm) + 2 * m
    stack = RasterStack(
        masks=np.zeros((len(problem.layers), ny, nx), dtype=bool),
        x0_nm=x0 - m * h_nm,
        y0_nm=y0 - m * h_nm,
        h_nm=h_nm,
        layer_names=problem.layer_names,
    )
    for li, layer in enumerate(problem.layers):
        for poly in layer.polygons:
            if poly.holes:
                pmask = np.zeros((ny, nx), dtype=bool)
                _paint_ring(stack, poly.outline, True, pmask)
                for hole in poly.holes:
                    _paint_ring(stack, hole, False, pmask)
                stack.masks[li] |= pmask
            else:
                # hole-less (e.g. a track outline): paint the layer mask
                # directly, skipping the full-frame temp
                _paint_ring(stack, poly.outline, True, stack.masks[li])

    # traces: wide ones are rasterized from their outline, sub-resolution
    # ones become exact 1D resistor chains along their centerline
    index = {name: li for li, name in enumerate(stack.layer_names)}
    narrow = []
    for seg in problem.tracks:
        li = index.get(seg.layer_name)
        if li is None:
            continue
        if seg.width_nm >= config.TRACK_1D_FACTOR * h_nm:
            _paint_ring(stack, seg.outline(config.ARC_TOL_FRACTION * h_nm),
                        True, stack.masks[li])
        else:
            narrow.append((li, seg))
    if narrow:
        n_links = _build_chains(stack, problem, narrow)
        print(f"{len(narrow)} trace(s) narrower than "
              f"{config.TRACK_1D_FACTOR:g} cells modeled as 1D resistor "
              f"chains ({n_links} links)")

    if problem.buildups:
        stack.buildup = np.zeros_like(stack.masks)
        index = {name: li for li, name in enumerate(stack.layer_names)}
        for b in problem.buildups:
            li = index.get(b.layer_name)
            if li is None:
                continue
            for poly in b.polygons:
                pmask = np.zeros((ny, nx), dtype=bool)
                _paint_ring(stack, poly.outline, True, pmask)
                for hole in poly.holes:
                    _paint_ring(stack, hole, False, pmask)
                stack.buildup[li] |= pmask
        stack.buildup &= stack.masks        # solder wets exposed copper only
    return stack


def _build_chains(stack: RasterStack, problem: Problem,
                  narrow: list) -> int:
    """Sub-resolution traces as 1D resistor chains: mark the cells their
    centerline crosses as copper and record one explicit conductance per
    pair of consecutive cells, allocating the trace's TRUE arc length to
    each link (a diagonal trace is not staircase-inflated). Links whose
    cells are already regular copper AND face-adjacent are skipped there
    (the trace merges into the pour: union, not sum). Returns the number
    of links."""
    L, ny, nx = stack.masks.shape
    plane = ny * nx
    h = stack.h_nm
    regular = stack.masks.copy()
    chain = np.zeros_like(stack.masks)
    aa, bb, gg, ll = [], [], [], []
    for li, seg in narrow:
        pts = seg.centerline(0.2 * h)
        d = np.hypot(*np.diff(pts, axis=0).T)
        s = np.concatenate([[0.0], np.cumsum(d)])
        length = float(s[-1])
        n_samp = max(2, int(math.ceil(length / (h / 3.0))) + 1)
        ss = np.linspace(0.0, length, n_samp)
        xs = np.interp(ss, s, pts[:, 0])
        ys = np.interp(ss, s, pts[:, 1])
        jj = np.floor((xs - stack.x0_nm) / h).astype(np.int64)
        ii = np.floor((ys - stack.y0_nm) / h).astype(np.int64)
        jj = np.clip(jj, 0, nx - 1)             # bbox includes all tracks;
        ii = np.clip(ii, 0, ny - 1)             # clip only guards rounding
        first = np.concatenate(
            [[True], (ii[1:] != ii[:-1]) | (jj[1:] != jj[:-1])])
        ci, cj, cs = ii[first], jj[first], ss[first]
        chain[li, ci, cj] = True
        g0 = (seg.width_nm * 1e-9
              * problem.layers[li].thickness_nm * 1e-9 / problem.rho_ohm_m)
        for k in range(len(ci) - 1):
            dl = (cs[k + 1] - cs[k]) * 1e-9
            if dl <= 0:
                continue
            adj4 = abs(int(ci[k + 1] - ci[k])) + abs(int(cj[k + 1] - cj[k])) == 1
            if adj4 and regular[li, ci[k], cj[k]] \
                    and regular[li, ci[k + 1], cj[k + 1]]:
                continue                        # pour conducts here already
            aa.append(li * plane + int(ci[k]) * nx + int(cj[k]))
            bb.append(li * plane + int(ci[k + 1]) * nx + int(cj[k + 1]))
            gg.append(g0 / dl)
            ll.append(li)
    stack.chain = chain & ~regular
    stack.masks |= stack.chain
    stack.chain_edges = (np.asarray(aa, dtype=np.int64),
                         np.asarray(bb, dtype=np.int64),
                         np.asarray(gg, dtype=float),
                         np.asarray(ll, dtype=np.int64))
    return len(aa)


def _rect_cells(stack: RasterStack, rect: Rect) -> np.ndarray:
    """Bool (ny, nx) mask of cells whose center lies inside the rectangle."""
    ny, nx = stack.shape2d
    h = stack.h_nm
    out = np.zeros((ny, nx), dtype=bool)
    j0 = max(0, int(math.ceil((rect.x0 - stack.x0_nm) / h - 0.5)))
    j1 = min(nx, int(math.floor((rect.x1 - stack.x0_nm) / h - 0.5)) + 1)
    i0 = max(0, int(math.ceil((rect.y0 - stack.y0_nm) / h - 0.5)))
    i1 = min(ny, int(math.floor((rect.y1 - stack.y0_nm) / h - 0.5)) + 1)
    if i0 < i1 and j0 < j1:
        out[i0:i1, j0:j1] = True
    return out


def _electrode_cells2d(stack: RasterStack, e: Electrode) -> np.ndarray:
    """2D footprint of the electrode shape (pad polygons or rectangle)."""
    if e.polygons:
        cells = np.zeros(stack.shape2d, dtype=bool)
        for poly in e.polygons:
            pm = np.zeros(stack.shape2d, dtype=bool)
            _paint_ring(stack, poly.outline, True, pm)
            for hole in poly.holes:
                _paint_ring(stack, hole, False, pm)
            cells |= pm
        if not cells.any():
            # shape smaller than one grid cell (small pad): use the cell
            # containing its center
            r = e.rect
            c = stack.cell_of((r.x0 + r.x1) / 2, (r.y0 + r.y1) / 2)
            if c is not None:
                cells[c] = True
        return cells
    return _rect_cells(stack, e.rect)


def electrode_masks(stack: RasterStack, problem: Problem
                    ) -> tuple[np.ndarray, np.ndarray]:
    """Terminal mask = OR over its parts; part = shape ∩ copper on the
    part's contact layer(s). contact 'all' = every included layer (bolted
    lug / through pad); a layer name = that layer only. Every part must
    individually land on copper (clear feedback). V+/V- must not overlap;
    touching is checked later, only for the equipotential contact model."""
    def build(parts: list[Electrode], which: str) -> np.ndarray:
        e = np.zeros_like(stack.masks)
        for el in parts:
            cells2d = _electrode_cells2d(stack, el)
            part = np.zeros_like(stack.masks)
            for li, name in enumerate(stack.layer_names):
                if el.contact == "all" or el.contact == name:
                    part[li] = cells2d & stack.masks[li]
            if not part.any():
                raise ElectrodeError(
                    f"A {which} contact part ({el.label}) does not overlap "
                    f"any copper of the selected fill on contact layer(s) "
                    f"'{el.contact}' (or is smaller than one grid cell)."
                )
            e |= part
        if not e.any():
            raise ElectrodeError(f"The {which} terminal has no contact parts.")
        return e

    e1 = build(problem.electrodes1, "V+")
    e2 = build(problem.electrodes2, "V-")

    if (e1 & e2).any():
        raise ElectrodeError(
            "The V+ and V- contact areas overlap on the copper grid. "
            "Move them apart."
        )
    return e1, e2


def electrode_partition(stack: RasterStack, problem: Problem
                        ) -> tuple[list, list]:
    """Per-part cell masks for both terminals, as [(label, mask3d), ...].
    Cells covered by several overlapping parts are attributed to the
    FIRST part (first-wins partition), so part currents sum exactly to
    the terminal current."""
    def build(parts: list[Electrode]) -> list:
        out = []
        claimed = np.zeros_like(stack.masks)
        for el in parts:
            cells2d = _electrode_cells2d(stack, el)
            m = np.zeros_like(stack.masks)
            for li, name in enumerate(stack.layer_names):
                if el.contact == "all" or el.contact == name:
                    m[li] = cells2d & stack.masks[li]
            m &= ~claimed
            claimed |= m
            out.append((el.label, m))
        return out

    return build(problem.electrodes1), build(problem.electrodes2)


def electrodes_touch(stack: RasterStack, e1: np.ndarray,
                     e2: np.ndarray) -> str | None:
    """Layer name where the terminals are 4-adjacent, or None."""
    for li in range(stack.nlayers):
        if (ndimage.binary_dilation(e1[li], structure=_STRUCT4) & e2[li]).any():
            return stack.layer_names[li]
    return None