import type { Field2D, Range } from "./field";
import { colormapTable, type Colormap } from "./colormap";

/**
 * Paint a field into RGBA pixels with y increasing upward (row 0 of the image is
 * the top of the plate, y = Ly). Non-finite values are drawn transparent.
 */
export function rasterizeField(
  field: Field2D,
  range: Range,
  cm: Colormap,
  out?: Uint8ClampedArray,
): Uint8ClampedArray {
  const { nx, ny, data } = field;
  const table = colormapTable(cm);
  const rgba = out && out.length === nx * ny * 4 ? out : new Uint8ClampedArray(nx * ny * 4);
  const span = range.max - range.min || 1;
  for (let i = 0; i < ny; i++) {
    const row = ny - 1 - i;
    for (let j = 0; j < nx; j++) {
      const v = data[i + j * ny];
      const px = (row * nx + j) * 4;
      if (!Number.isFinite(v)) {
        rgba[px + 3] = 0;
        continue;
      }
      let t = (v - range.min) / span;
      t = t < 0 ? 0 : t > 1 ? 1 : t;
      const k = Math.round(t * 255) * 3;
      rgba[px] = table[k];
      rgba[px + 1] = table[k + 1];
      rgba[px + 2] = table[k + 2];
      rgba[px + 3] = 255;
    }
  }
  return rgba;
}