Robustify is_paused and hold_render logic

bokehjs/src/lib/models/plots/plot_canvas.ts

@@ -114,8 +114,6 @@ export class PlotView extends LayoutDOMView implements Paintable {
     this._range_manager.invalidate_dataranges = value
   }
 
-  protected _is_paused?: number
-
   protected lod_started: boolean
 
   protected _initial_state: StateInfo
@@ -168,29 +166,22 @@ export class PlotView extends LayoutDOMView implements Paintable {
     yield* this.tool_views.values()
   }
 
-  get is_paused(): boolean {
-    return this._is_paused != null && this._is_paused !== 0
-  }
-
   get child_models(): LayoutDOM[] {
     return []
   }
 
+  private _is_paused: number = 0
+  get is_paused(): boolean {
+    return this._is_paused != 0
+  }
+
   pause(): void {
-    if (this._is_paused == null) {
-      this._is_paused = 1
-    } else {
-      this._is_paused += 1
-    }
+    this._is_paused += 1
   }
 
   unpause(no_render: boolean = false): void {
-    if (this._is_paused == null) {
-      throw new Error("wasn't paused")
-    }
-
-    this._is_paused = Math.max(this._is_paused - 1, 0)
-    if (this._is_paused == 0 && !no_render) {
+    this._is_paused = max(this._is_paused - 1, 0)
+    if (!this.is_paused && !no_render) {
       this.request_repaint()
     }
   }
@@ -869,7 +860,11 @@ export class PlotView extends LayoutDOMView implements Paintable {
     })
 
     const {hold_render} = this.model.properties
-    this.on_change(hold_render, () => this._hold_render_changed())
+    this.on_change(hold_render, () => {
+      if (!this.model.hold_render) {
+        this.request_repaint()
+      }
+    })
   }
 
   override has_finished(): boolean {
@@ -972,7 +967,7 @@ export class PlotView extends LayoutDOMView implements Paintable {
   }
 
   paint(): void {
-    if (this.is_paused) {
+    if (this.is_paused || this.model.hold_render) {
       return
     }
 
@@ -1198,14 +1193,6 @@ export class PlotView extends LayoutDOMView implements Paintable {
     return {...state, children: [...children ?? [], frame, ...renderers]}
   }
 
-  protected _hold_render_changed(): void {
-    if (this.model.hold_render) {
-      this.pause()
-    } else {
-      this.unpause()
-    }
-  }
-
   override resolve_frame(): View | null {
     return this.frame as any // TODO CartesianFrameView (PR #13286)
   }

bokehjs/test/integration/plots.ts

@@ -356,11 +356,11 @@ describe("Plot", () => {
       p.hold_render = false
       await view.ready
 
-      // TODO: expect(spy.callCount).to.be.equal(1)
-      //
-      // There should be exactly one paint after all this, but currently
-      // it varies between 2 and 3, due to layout and other factors. It's
-      // sufficient though, to compare images for a complete test.
+      // Two _actual_paint() calls because of how layout is integrated into
+      // the painting pipeline. This doesn't mean that renderers are actually
+      // painted twice, because paint invalidation logic prevents this. It's
+      // still quite confusing and requires a redesign.
+      expect(spy.callCount).to.be.equal(2)
     })
   })
 })