perf: add gpu hint and transform settle to prevent rasterizing while zooming (scale transform) (#7417)

## Summary

Ensures the nodes get their own compositing layers during scale
transform (tracked via mouse wheel events), which prevents rasterization
during transform. Adds forced reflow at end of transform to ensure
layers are always at correct resolution (fixes blurriness and some
readability issues).

Videos show testing this branch first then testing main - doing layer
visualization, paint (include paint operations calculations and actual
raster) visualizations, and cpu usage monitoring.


https://github.com/user-attachments/assets/c5fab219-0b32-4822-9238-c4572f0d6a44



https://github.com/user-attachments/assets/7e172e8d-cc5b-4dcd-aa07-1dfc3eb65bac

src/renderer/core/layout/__tests__/TransformPane.test.ts

@@ -117,6 +117,73 @@ describe('TransformPane', () => {
     })
   })
 
+  describe('canvas event listeners', () => {
+    it('should add event listeners to canvas on mount', async () => {
+      const mockCanvas = createMockCanvas()
+      mount(TransformPane, {
+        props: {
+          canvas: mockCanvas
+        }
+      })
+
+      await nextTick()
+
+      expect(mockCanvas.canvas.addEventListener).toHaveBeenCalledWith(
+        'wheel',
+        expect.any(Function),
+        expect.any(Object)
+      )
+      expect(mockCanvas.canvas.addEventListener).not.toHaveBeenCalledWith(
+        'pointerdown',
+        expect.any(Function),
+        expect.any(Object)
+      )
+      expect(mockCanvas.canvas.addEventListener).not.toHaveBeenCalledWith(
+        'pointerup',
+        expect.any(Function),
+        expect.any(Object)
+      )
+      expect(mockCanvas.canvas.addEventListener).not.toHaveBeenCalledWith(
+        'pointercancel',
+        expect.any(Function),
+        expect.any(Object)
+      )
+    })
+
+    it('should remove event listeners on unmount', async () => {
+      const mockCanvas = createMockCanvas()
+      const wrapper = mount(TransformPane, {
+        props: {
+          canvas: mockCanvas
+        }
+      })
+
+      await nextTick()
+      wrapper.unmount()
+
+      expect(mockCanvas.canvas.removeEventListener).toHaveBeenCalledWith(
+        'wheel',
+        expect.any(Function),
+        expect.any(Object)
+      )
+      expect(mockCanvas.canvas.removeEventListener).not.toHaveBeenCalledWith(
+        'pointerdown',
+        expect.any(Function),
+        expect.any(Object)
+      )
+      expect(mockCanvas.canvas.removeEventListener).not.toHaveBeenCalledWith(
+        'pointerup',
+        expect.any(Function),
+        expect.any(Object)
+      )
+      expect(mockCanvas.canvas.removeEventListener).not.toHaveBeenCalledWith(
+        'pointercancel',
+        expect.any(Function),
+        expect.any(Object)
+      )
+    })
+  })
+
   describe('interaction state management', () => {
     it('should apply interacting class during interactions', async () => {
       const mockCanvas = createMockCanvas()
@@ -131,7 +198,9 @@ describe('TransformPane', () => {
       const transformPane = wrapper.find('[data-testid="transform-pane"]')
 
       // Initially should not have interacting class
-      expect(transformPane.classes()).not.toContain('will-change-transform')
+      expect(transformPane.classes()).not.toContain(
+        'transform-pane--interacting'
+      )
     })
 
     it('should handle pointer events for node delegation', async () => {

src/renderer/core/layout/transform/TransformPane.vue

@@ -1,7 +1,12 @@
 <template>
   <div
     data-testid="transform-pane"
-    class="absolute inset-0 w-full h-full pointer-events-none"
+    :class="
+      cn(
+        'absolute inset-0 w-full h-full pointer-events-none',
+        isInteracting ? 'transform-pane--interacting' : 'will-change-auto'
+      )
+    "
     :style="transformStyle"
   >
     <!-- Vue nodes will be rendered here -->
@@ -11,9 +16,12 @@
 
 <script setup lang="ts">
 import { useRafFn } from '@vueuse/core'
+import { computed } from 'vue'
 
 import type { LGraphCanvas } from '@/lib/litegraph/src/litegraph'
+import { useTransformSettling } from '@/renderer/core/layout/transform/useTransformSettling'
 import { useTransformState } from '@/renderer/core/layout/transform/useTransformState'
+import { cn } from '@/utils/tailwindUtil'
 
 interface TransformPaneProps {
   canvas?: LGraphCanvas
@@ -23,6 +31,11 @@ const props = defineProps<TransformPaneProps>()
 
 const { transformStyle, syncWithCanvas } = useTransformState()
 
+const canvasElement = computed(() => props.canvas?.canvas)
+const { isTransforming: isInteracting } = useTransformSettling(canvasElement, {
+  settleDelay: 16
+})
+
 useRafFn(
   () => {
     if (!props.canvas) {
@@ -33,3 +46,9 @@ useRafFn(
   { immediate: true }
 )
 </script>
+
+<style scoped>
+.transform-pane--interacting {
+  will-change: transform;
+}
+</style>

src/renderer/core/layout/transform/useTransformSettling.ts

@@ -0,0 +1,84 @@
+import { useDebounceFn, useEventListener } from '@vueuse/core'
+import { ref } from 'vue'
+import type { MaybeRefOrGetter } from 'vue'
+
+interface TransformSettlingOptions {
+  /**
+   * Delay in ms before transform is considered "settled" after last interaction
+   * @default 200
+   */
+  settleDelay?: number
+  /**
+   * Whether to use passive event listeners (better performance but can't preventDefault)
+   * @default true
+   */
+  passive?: boolean
+}
+
+/**
+ * Tracks when canvas zoom transforms are actively changing vs settled.
+ *
+ * This composable helps optimize rendering quality during zoom transformations.
+ * When the user is actively zooming, we can reduce rendering quality
+ * for better performance. Once the transform "settles" (stops changing), we can
+ * trigger high-quality re-rasterization.
+ *
+ * The settling concept prevents constant quality switching during interactions
+ * by waiting for a period of inactivity before considering the transform complete.
+ *
+ * Uses VueUse's useEventListener for automatic cleanup and useDebounceFn for
+ * efficient settle detection.
+ *
+ * @example
+ * ```ts
+ * const { isTransforming } = useTransformSettling(canvasRef, {
+ *   settleDelay: 200
+ * })
+ *
+ * // Use in CSS classes or rendering logic
+ * const cssClass = computed(() => ({
+ *   'low-quality': isTransforming.value,
+ *   'high-quality': !isTransforming.value
+ * }))
+ * ```
+ */
+export function useTransformSettling(
+  target: MaybeRefOrGetter<HTMLElement | null | undefined>,
+  options: TransformSettlingOptions = {}
+) {
+  const { settleDelay = 256, passive = true } = options
+
+  const isTransforming = ref(false)
+
+  /**
+   * Mark transform as active
+   */
+  const markTransformActive = () => {
+    isTransforming.value = true
+  }
+
+  /**
+   * Mark transform as settled (debounced)
+   */
+  const markTransformSettled = useDebounceFn(() => {
+    isTransforming.value = false
+  }, settleDelay)
+
+  /**
+   * Handle zoom transform event - mark active then queue settle
+   */
+  const handleWheel = () => {
+    markTransformActive()
+    void markTransformSettled()
+  }
+
+  // Register wheel event listener with auto-cleanup
+  useEventListener(target, 'wheel', handleWheel, {
+    capture: true,
+    passive
+  })
+
+  return {
+    isTransforming
+  }
+}