chore: refactor zoom calculation from viewport

packages/mui/src/utils/contentworker.ts

@@ -16,6 +16,7 @@ import {
   scalePoints,
   translatePoints,
   copyRect,
+  zoomFromViewport,
 } from "./geometry";
 import { Rect } from "@micahg/tbltp-common";
 
@@ -177,30 +178,7 @@ function adjustZoomFromViewport() {
   // set our viewport to the initial value requested
   copyRect(_img_orig, _img);
 
-  // unrotate canvas
-  const [cW, cH] = rotatedWidthAndHeight(
-    -_angle,
-    _canvas.width,
-    _canvas.height,
-  );
-  const zW = _img.width / cW;
-  const zH = _img.height / cH;
-
-  // set zoom and offset x or y to compensate for viewport
-  // aspect ratios that are different from the screen
-  if (zH > zW) {
-    _zoom = zH;
-    const adj = cW * _zoom;
-    if (adj < _fullRotW) {
-      _img.x -= (adj - _img.width) / 2;
-    }
-  } else {
-    _zoom = zW;
-    const adj = cH * _zoom;
-    if (adj < _fullRotH) {
-      _img.y -= (adj - _img.height) / 2;
-    }
-  }
+  _zoom = zoomFromViewport(_angle, _canvas.width, _canvas.height, _img);
 }
 
 /**

packages/mui/src/utils/geometry.ts

@@ -204,6 +204,32 @@ export function translatePoints(points: Point[], x: number, y: number) {
   return tPoints;
 }
 
+/**
+ * Given a desired viewport, set our current viewport accordingly, set the zoom,
+ * and then center the request viewport within our screen, extending its short
+ * side to fit our screen.
+ *
+ * This is used when the remote client is told which region to display, rather
+ * than in the editor, where (iirc) you calculate the viewpoint given a point,
+ * a zoom level and the canvas size.
+ */
+export function zoomFromViewport(
+  angle: number,
+  containerWidth: number,
+  containerHeight: number,
+  img: Rect,
+) {
+  // un-rotate canvas
+  const [cW, cH] = rotatedWidthAndHeight(
+    -angle,
+    containerWidth,
+    containerHeight,
+  );
+  const zW = img.width / cW;
+  const zH = img.height / cH;
+  return Math.max(zW, zH);
+}
+
 /**
  * rotate and fill viewport to fit screen/window/canvas
  * @param screen screen [width, height]