Add anchored zodiac artwork

plugin/contents/ui/constellation-art/LICENSE.md

@@ -0,0 +1,11 @@
+# Stellarium Modern constellation illustrations
+
+The twelve PNG illustrations in this directory are taken from the
+[Stellarium Modern sky culture](https://github.com/Stellarium/stellarium/tree/master/skycultures/modern/illustrations).
+
+The Stellarium sky-culture description licenses the illustrations under the
+[Free Art License 1.3](https://artlibre.org/licence/lal/en/).
+
+The images are redistributed here with their original names and are rendered
+with an affine transformation so their three Hipparcos anchor stars remain
+aligned with the simulated sky.

plugin/contents/ui/dancer.html

@@ -1219,6 +1219,17 @@ const ctx    = canvas.getContext('2d');
 
 let obsLat = -24.72, obsLon = -53.74;  // Toledo-PR; sobrescrito pela config
 let showConstellations = false;
+const constellationArtImages = new Map();
+if (typeof CONSTELLATIONS !== 'undefined') {
+  for (const constellation of CONSTELLATIONS) {
+    if (!constellation.art) continue;
+    const img = new Image();
+    img.onload = () => projectSky();
+    img.onerror = () => console.error('[skeledance] falha na arte de ' + constellation.name);
+    img.src = constellation.art.file;
+    constellationArtImages.set(constellation.id, img);
+  }
+}
 const VIEW_AZ     = 90;     // centro da tela olha para o LESTE — a tela física do
                             // usuário está voltada p/ leste, então o wallpaper age
                             // como janela: estrelas nascem subindo dentro da cena
@@ -1400,8 +1411,62 @@ function renderMilkyWay(lstDeg, glareOn) {
   return true;
 }
 
+/* Resolve a transformação afim que prende três pixels da ilustração às suas
+   três estrelas Hipparcos projetadas. */
+function constellationArtTransform(source, target) {
+  const [p1, p2, p3] = source;
+  const [q1, q2, q3] = target;
+  const den = p1[0] * (p2[1] - p3[1]) + p2[0] * (p3[1] - p1[1]) +
+              p3[0] * (p1[1] - p2[1]);
+  if (Math.abs(den) < 1e-6) return null;
+  const solve = (v1, v2, v3) => ({
+    x: (v1 * (p2[1] - p3[1]) + v2 * (p3[1] - p1[1]) +
+        v3 * (p1[1] - p2[1])) / den,
+    y: (v1 * (p3[0] - p2[0]) + v2 * (p1[0] - p3[0]) +
+        v3 * (p2[0] - p1[0])) / den,
+    t: (v1 * (p2[0] * p3[1] - p3[0] * p2[1]) +
+        v2 * (p3[0] * p1[1] - p1[0] * p3[1]) +
+        v3 * (p1[0] * p2[1] - p2[0] * p1[1])) / den,
+  });
+  const x = solve(q1.x, q2.x, q3.x);
+  const y = solve(q1.y, q2.y, q3.y);
+  return [x.x, y.x, x.y, y.y, x.t, y.t];
+}
+
+function drawConstellationArt(c, constellation, lst, W, horizonPx) {
+  const art = constellation.art;
+  const img = constellationArtImages.get(constellation.id);
+  if (!art || !img || !img.complete || !img.naturalWidth) return;
+
+  const target = art.anchors.map(anchor => {
+    const aa = altAz(anchor.sky[0], anchor.sky[1], lst);
+    const daz = ((aa.az - VIEW_AZ) % 360 + 540) % 360 - 180;
+    return {
+      x: (0.5 + daz / FOV_AZ) * W,
+      y: horizonPx * (1 - aa.alt / ALT_TOP),
+      alt: aa.alt,
+    };
+  });
+  if (target.every(p => p.alt < -8) || target.every(p => p.alt > ALT_TOP + 8)) return;
+
+  const matrix = constellationArtTransform(
+    art.anchors.map(anchor => anchor.pos), target
+  );
+  if (!matrix || matrix.some(v => !Number.isFinite(v))) return;
+
+  c.save();
+  c.beginPath();
+  c.rect(0, 0, W, horizonPx);
+  c.clip();
+  c.globalCompositeOperation = 'screen';
+  c.globalAlpha = 0.19;
+  c.setTransform(...matrix);
+  c.drawImage(img, 0, 0, art.size[0], art.size[1]);
+  c.restore();
+}
+
 /* Figuras convencionais dos 12 signos zodiacais, ancoradas em RA/Dec J2000.
-   São desenhadas antes das estrelas para os pontos reais ficarem por cima. */
+   Arte, linhas e estrelas reais ficam sobrepostas nesta ordem. */
 function drawConstellations(c, lst, W, H, horizonPx) {
   if (!showConstellations || typeof CONSTELLATIONS === 'undefined') return;
   const rankAlpha = [0, 0.52, 0.38, 0.25];
@@ -1412,6 +1477,9 @@ function drawConstellations(c, lst, W, H, horizonPx) {
   c.lineJoin = 'round';
   c.shadowColor = 'rgba(60,185,255,0.65)';
   c.shadowBlur = 7;
+  for (const constellation of CONSTELLATIONS) {
+    drawConstellationArt(c, constellation, lst, W, horizonPx);
+  }
   for (const constellation of CONSTELLATIONS) {
     const rank = Math.max(1, Math.min(3, constellation.rank || 3));
     c.strokeStyle = `rgba(105,205,255,${rankAlpha[rank]})`;