fix webgl context loss handling

src/mol-canvas3d/canvas3d.ts

@@ -129,7 +129,8 @@ namespace Canvas3DContext {
         if (isDebugMode) {
             const loseContextExt = gl.getExtension('WEBGL_lose_context');
             if (loseContextExt) {
-                /** Hold down shift+ctrl+alt and press any mouse button to trigger lose context */
+                // Hold down shift+ctrl+alt and press any mouse button to call `loseContext`.
+                // After 1 second `restoreContext` will be called.
                 canvas.addEventListener('mousedown', e => {
                     if (webgl.isContextLost) return;
                     if (!e.shiftKey || !e.ctrlKey || !e.altKey) return;
@@ -159,7 +160,9 @@ namespace Canvas3DContext {
 
         const handlewWebglContextRestored = () => {
             if (!webgl.isContextLost) return;
-            webgl.handleContextRestored();
+            webgl.handleContextRestored(() => {
+                passes.draw.reset();
+            });
             if (isDebugMode) console.log('context restored');
         };
 
@@ -599,6 +602,10 @@ namespace Canvas3D {
         const contextRestoredSub = contextRestored.subscribe(() => {
             pickHelper.dirty = true;
             draw(true);
+            // Unclear why, but in Chrome with wboit enabled the first `draw` only clears
+            // the drawingBuffer. Note that in Firefox the drawingBuffer is preserved after
+            // context loss so it is unclear if it behaves the same.
+            draw(true);
         });
 
         const resized = new BehaviorSubject<any>(0);

src/mol-canvas3d/passes/draw.ts

@@ -95,6 +95,10 @@ export class DrawPass {
         this.wboit = enableWboit ? new WboitPass(webgl, width, height) : undefined;
     }
 
+    reset() {
+        this.wboit?.reset();
+    }
+
     setSize(width: number, height: number) {
         const w = this.colorTarget.getWidth();
         const h = this.colorTarget.getHeight();

src/mol-canvas3d/passes/wboit.ts

@@ -89,13 +89,37 @@ export class WboitPass {
         }
     }
 
-    constructor(private webgl: WebGLContext, width: number, height: number) {
-        const { resources, extensions } = webgl;
-        const { drawBuffers, textureFloat, colorBufferFloat, depthTexture } = extensions;
+    reset() {
+        if (this._enabled) this._init();
+    }
+
+    private _init() {
+        const { extensions: { drawBuffers } } = this.webgl;
+
+        this.framebuffer.bind();
+        drawBuffers!.drawBuffers([
+            drawBuffers!.COLOR_ATTACHMENT0,
+            drawBuffers!.COLOR_ATTACHMENT1,
+        ]);
+
+        this.textureA.attachFramebuffer(this.framebuffer, 'color0');
+        this.textureB.attachFramebuffer(this.framebuffer, 'color1');
+    }
+
+    static isSupported(webgl: WebGLContext) {
+        const { extensions: { drawBuffers, textureFloat, colorBufferFloat, depthTexture } } = webgl;
         if (!textureFloat || !colorBufferFloat || !depthTexture || !drawBuffers) {
             if (isDebugMode) console.log('Missing extensions required for "wboit"');
-            return;
+            return false;
+        } else {
+            return true;
         }
+    }
+
+    constructor(private webgl: WebGLContext, width: number, height: number) {
+        if (!WboitPass.isSupported(webgl)) return;
+
+        const { resources } = webgl;
 
         this.textureA = resources.texture('image-float32', 'rgba', 'float', 'nearest');
         this.textureA.define(width, height);
@@ -104,17 +128,8 @@ export class WboitPass {
         this.textureB.define(width, height);
 
         this.renderable = getEvaluateWboitRenderable(webgl, this.textureA, this.textureB);
-
         this.framebuffer = resources.framebuffer();
-        this.framebuffer.bind();
-        drawBuffers.drawBuffers([
-            drawBuffers.COLOR_ATTACHMENT0,
-            drawBuffers.COLOR_ATTACHMENT1,
-        ]);
-
-        this.textureA.attachFramebuffer(this.framebuffer, 'color0');
-        this.textureB.attachFramebuffer(this.framebuffer, 'color1');
-
+        this._init();
         this._enabled = true;
     }
 }
\ No newline at end of file

src/mol-gl/webgl/context.ts

@@ -193,7 +193,7 @@ export interface WebGLContext {
     readonly isContextLost: boolean
     readonly contextRestored: BehaviorSubject<now.Timestamp>
     setContextLost: () => void
-    handleContextRestored: () => void
+    handleContextRestored: (extraResets?: () => void) => void
 
     /** Cache for compute renderables, managed by consumers */
     readonly namedComputeRenderables: { [name: string]: ComputeRenderable<any> }
@@ -302,7 +302,7 @@ export function createContext(gl: GLRenderingContext, props: Partial<{ pixelScal
         setContextLost: () => {
             isContextLost = true;
         },
-        handleContextRestored: () => {
+        handleContextRestored: (extraResets?: () => void) => {
             Object.assign(extensions, createExtensions(gl));
 
             state.reset();
@@ -312,6 +312,7 @@ export function createContext(gl: GLRenderingContext, props: Partial<{ pixelScal
 
             resources.reset();
             renderTargets.forEach(rt => rt.reset());
+            extraResets?.();
 
             isContextLost = false;
             contextRestored.next(now());

src/mol-gl/webgl/texture.ts

@@ -329,7 +329,9 @@ export function createTexture(gl: GLRenderingContext, extensions: WebGLExtension
             texture = getTexture(gl);
             init();
 
-            define(width, height, depth);
+            const [_width, _height, _depth] = [width, height, depth];
+            width = 0, height = 0, depth = 0; // set to zero to trigger resize
+            define(_width, _height, _depth);
             if (loadedData) load(loadedData);
         },
         destroy: () => {