GPU accelerated maskeditor rendering (#6767)

## GPU accelerated brush engine for the mask editor

- Full GPU acceleration using TypeGPU and type-safe shaders
- Catmull-Rom Spline Smoothing
- arc-length equidistant resampling
- much improved performance, even for huge images
- photoshop like opacity clamping for brush strokes
- much improved soft brushes
- fallback to CPU fully implemented, much improved CPU rendering
features as well

### Tested Browsers
- Chrome (fully supported)
- Safari 26 (fully supported, prev versions CPU fallback)
- Firefox (CPU fallback, flags needed for full support)



https://github.com/user-attachments/assets/b7b5cb8a-2290-4a95-ae7d-180e11fccdb0



https://github.com/user-attachments/assets/4297aaa5-f249-499a-9b74-869677f1c73b



https://github.com/user-attachments/assets/602b4783-3e2b-489e-bcb9-70534bcaac5e

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6767-GPU-accelerated-maskeditor-rendering-2b16d73d3650818cb294e1fca03f6169)
by [Unito](https://www.unito.io)

src/components/maskeditor/BrushCursor.vue

@@ -26,6 +26,10 @@
 <script setup lang="ts">
 import { computed } from 'vue'
 
+import {
+  getEffectiveBrushSize,
+  getEffectiveHardness
+} from '@/composables/maskeditor/brushUtils'
 import { BrushShape } from '@/extensions/core/maskeditor/types'
 import { useMaskEditorStore } from '@/stores/maskEditorStore'
 
@@ -36,11 +40,14 @@ const { containerRef } = defineProps<{
 const store = useMaskEditorStore()
 
 const brushOpacity = computed(() => {
-  return store.brushVisible ? '1' : '0'
+  return store.brushVisible ? 1 : 0
 })
 
 const brushRadius = computed(() => {
-  return store.brushSettings.size * store.zoomRatio
+  const size = store.brushSettings.size
+  const hardness = store.brushSettings.hardness
+  const effectiveSize = getEffectiveBrushSize(size, hardness)
+  return effectiveSize * store.zoomRatio
 })
 
 const brushSize = computed(() => {
@@ -78,19 +85,26 @@ const gradientVisible = computed(() => {
 })
 
 const gradientBackground = computed(() => {
+  const size = store.brushSettings.size
   const hardness = store.brushSettings.hardness
+  const effectiveSize = getEffectiveBrushSize(size, hardness)
+  const effectiveHardness = getEffectiveHardness(size, hardness, effectiveSize)
 
-  if (hardness === 1) {
+  if (effectiveHardness === 1) {
     return 'rgba(255, 0, 0, 0.5)'
   }
 
-  const midStop = hardness * 100
+  const midStop = effectiveHardness * 100
   const outerStop = 100
+  // Add an intermediate stop to approximate the squared falloff
+  // At 50% of the fade region, squared falloff is 0.25 (relative to max)
+  const fadeMidStop = midStop + (outerStop - midStop) * 0.5
 
   return `radial-gradient(
     circle,
     rgba(255, 0, 0, 0.5) 0%,
-    rgba(255, 0, 0, 0.25) ${midStop}%,
+    rgba(255, 0, 0, 0.5) ${midStop}%,
+    rgba(255, 0, 0, 0.125) ${fadeMidStop}%,
     rgba(255, 0, 0, 0) ${outerStop}%
   )`
 })

src/components/maskeditor/BrushSettingsPanel.vue

@@ -55,7 +55,7 @@
     <SliderControl
       :label="t('maskEditor.thickness')"
       :min="1"
-      :max="100"
+      :max="500"
       :step="1"
       :model-value="store.brushSettings.size"
       @update:model-value="onThicknessChange"
@@ -80,12 +80,12 @@
     />
 
     <SliderControl
-      :label="t('maskEditor.smoothingPrecision')"
+      label="Stepsize"
       :min="1"
       :max="100"
       :step="1"
-      :model-value="store.brushSettings.smoothingPrecision"
-      @update:model-value="onSmoothingPrecisionChange"
+      :model-value="store.brushSettings.stepSize"
+      @update:model-value="onStepSizeChange"
     />
   </div>
 </template>
@@ -119,8 +119,8 @@ const onHardnessChange = (value: number) => {
   store.setBrushHardness(value)
 }
 
-const onSmoothingPrecisionChange = (value: number) => {
-  store.setBrushSmoothingPrecision(value)
+const onStepSizeChange = (value: number) => {
+  store.setBrushStepSize(value)
 }
 
 const resetToDefault = () => {

src/components/maskeditor/MaskEditorContent.vue

@@ -12,19 +12,28 @@
     >
       <canvas
         ref="imgCanvasRef"
-        class="absolute top-0 left-0 w-full h-full"
+        class="absolute top-0 left-0 w-full h-full z-0"
         @contextmenu.prevent
       />
       <canvas
         ref="rgbCanvasRef"
-        class="absolute top-0 left-0 w-full h-full"
+        class="absolute top-0 left-0 w-full h-full z-10"
         @contextmenu.prevent
       />
       <canvas
         ref="maskCanvasRef"
-        class="absolute top-0 left-0 w-full h-full"
+        class="absolute top-0 left-0 w-full h-full z-30"
         @contextmenu.prevent
       />
+      <!-- GPU Preview Canvas -->
+      <canvas
+        ref="gpuCanvasRef"
+        class="absolute top-0 left-0 w-full h-full pointer-events-none"
+        :class="{
+          'z-20': store.activeLayer === 'rgb',
+          'z-40': store.activeLayer === 'mask'
+        }"
+      />
       <div ref="canvasBackgroundRef" class="bg-white w-full h-full" />
     </div>
 
@@ -87,6 +96,7 @@ const canvasContainerRef = ref<HTMLDivElement>()
 const imgCanvasRef = ref<HTMLCanvasElement>()
 const maskCanvasRef = ref<HTMLCanvasElement>()
 const rgbCanvasRef = ref<HTMLCanvasElement>()
+const gpuCanvasRef = ref<HTMLCanvasElement>()
 const canvasBackgroundRef = ref<HTMLDivElement>()
 
 const toolPanelRef = ref<InstanceType<typeof ToolPanel>>()
@@ -97,7 +107,7 @@ const initialized = ref(false)
 const keyboard = useKeyboard()
 const panZoom = usePanAndZoom()
 
-let toolManager: ReturnType<typeof useToolManager> | null = null
+const toolManager = useToolManager(keyboard, panZoom)
 
 let resizeObserver: ResizeObserver | null = null
 
@@ -135,8 +145,6 @@ const initUI = async () => {
   try {
     await loader.loadFromNode(node)
 
-    toolManager = useToolManager(keyboard, panZoom)
-
     const imageLoader = useImageLoader()
     const image = await imageLoader.loadImages()
 
@@ -149,6 +157,18 @@ const initUI = async () => {
 
     store.canvasHistory.saveInitialState()
 
+    // Initialize GPU resources
+    if (toolManager.brushDrawing) {
+      await toolManager.brushDrawing.initGPUResources()
+      if (gpuCanvasRef.value && toolManager.brushDrawing.initPreviewCanvas) {
+        // Match preview canvas resolution to mask canvas
+        gpuCanvasRef.value.width = maskCanvasRef.value.width
+        gpuCanvasRef.value.height = maskCanvasRef.value.height
+
+        toolManager.brushDrawing.initPreviewCanvas(gpuCanvasRef.value)
+      }
+    }
+
     initialized.value = true
   } catch (error) {
     console.error('[MaskEditorContent] Initialization failed:', error)
@@ -172,7 +192,7 @@ onMounted(() => {
 })
 
 onBeforeUnmount(() => {
-  toolManager?.brushDrawing.saveBrushSettings()
+  toolManager.brushDrawing.saveBrushSettings()
 
   keyboard?.removeListeners()
 

src/components/maskeditor/dialog/TopBarHeader.vue

@@ -102,6 +102,7 @@ const onInvert = () => {
 
 const onClear = () => {
   canvasTools.clearMask()
+  store.triggerClear()
 }
 
 const handleSave = async () => {