Fixed odd red and blue screenshot artifacts

Author: shai-almog

Ports/JavaScriptPort/STATUS.md

@@ -18,6 +18,7 @@ Current State
 - New patch (not yet CI-validated in this document revision): worker-side fallback screenshot path now waits for a host-side UI-settle barrier before ready-callback dispatch and before canvas capture, to avoid pre-paint frame capture.
 - Note: a short-lived `forceShow()` experiment in `BaseTest.registerReadyCallback` was reverted because it caused re-entrant callback loops and prevented `CN1SS:SUITE:FINISHED`.
 - New patch (not yet CI-validated in this document revision): host screenshot capture now tracks the real draw target canvas and includes off-DOM canvases reachable via host refs.
+- New patch (not yet CI-validated in this document revision): screenshot candidate selection now prioritizes near-screen-sized canvases to prevent tiny offscreen buffers from being selected (fixes unexpected `120x80`/`4x4` outputs).
 
 What Was Fixed In This Pass
 ---------------------------
@@ -111,6 +112,19 @@ What Was Fixed In This Pass
    - Motivation:
      - Current logs show active drawing calls while DOM-canvas snapshots remain static/white; this addresses likely off-DOM/back-buffer capture misses.
 
+10. Added large-canvas gating for screenshot candidate selection.
+   - File:
+     - `vm/ByteCodeTranslator/src/javascript/browser_bridge.js`
+   - Changes:
+     - Evaluate all candidate canvases, compute max area, and prefer candidates with area >= 45% of max (with floor at 65536).
+     - Only fall back to tiny-canvas pool if no large candidates exist.
+     - Added diagnostics:
+       - `PARPAR:DIAG:SCREENSHOT_START:canvasConsidered=...`
+       - `PARPAR:DIAG:SCREENSHOT_START:canvasLargeCount=...`
+       - `PARPAR:DIAG:SCREENSHOT_START:canvasMinLargeArea=...`
+   - Motivation:
+     - Latest artifacts showed mixed dimensions (`120x80`, `4x4`) and colored tiny captures, indicating offscreen utility buffers were being selected.
+
 Known Failing Symptoms (Latest CI Logs/Artifacts)
 -------------------------------------------------
 
@@ -135,7 +149,9 @@ Priority Next Steps
 1. Validate CI output after UI-settle barrier:
    - Expect non-identical PNG hashes for distinct tests.
    - Confirm `settleChanged`, `canvasSig`, and `canvasSource` diagnostics vary across tests.
-2. If white-frame reuse persists, capture and compare per-test `settleSig`/`canvasSig`/`canvasSource` to identify whether paint is not happening or capture target is still wrong.
+2. Validate size normalization after large-canvas gating:
+   - Expect screenshot dimensions to remain consistent at app target size (no `120x80`/`4x4` non-bootstrap outputs).
+3. If white-frame reuse persists, capture and compare per-test `settleSig`/`canvasSig`/`canvasSource` to identify whether paint is not happening or capture target is still wrong.
 3. Fix per-test null receiver/init path (`__classDef` null) at first failing stack, not via broad fallbacks.
 4. Fix missing `Button.initLaf(UIManager)` symbol resolution in worker runtime path.
 5. Fix worker-mode orientation lock path so DOM access is host-bridge mediated (no direct `document` access in worker).

vm/ByteCodeTranslator/src/javascript/browser_bridge.js

@@ -505,12 +505,8 @@
     if (!candidates.length) {
       return null;
     }
-    var best = null;
-    var bestArea = -1;
-    var bestScore = -1;
-    var bestIndex = -1;
-    var bestSource = 'none';
-    var bestSignature = 'none';
+    var evaluated = [];
+    var maxArea = -1;
     for (var i = 0; i < candidates.length; i++) {
       var c = candidates[i].canvas;
       if (!c || (includeDataUrl && typeof c.toDataURL !== 'function')) {
@@ -522,20 +518,58 @@
       var scoreMeta = canvasContentScore(c);
       var score = scoreMeta && scoreMeta.score != null ? (scoreMeta.score | 0) : -1;
       var signature = scoreMeta && scoreMeta.signature ? String(scoreMeta.signature) : 'none';
-      if (score > bestScore || (score === bestScore && area > bestArea)) {
-        bestScore = score;
-        bestArea = area;
-        best = c;
-        bestIndex = i;
-        bestSource = candidates[i].source || 'unknown';
-        bestSignature = signature;
+      evaluated.push({
+        canvas: c,
+        index: i,
+        source: candidates[i].source || 'unknown',
+        area: area,
+        score: score,
+        signature: signature,
+        width: w,
+        height: h
+      });
+      if (area > maxArea) {
+        maxArea = area;
+      }
+    }
+    if (!evaluated.length) {
+      return null;
+    }
+    var minLargeArea = Math.max(65536, Math.floor(maxArea * 0.45));
+    var pool = [];
+    for (var p = 0; p < evaluated.length; p++) {
+      if (evaluated[p].area >= minLargeArea) {
+        pool.push(evaluated[p]);
+      }
+    }
+    if (!pool.length) {
+      pool = evaluated;
+    }
+    var best = null;
+    var bestArea = -1;
+    var bestScore = -1;
+    var bestIndex = -1;
+    var bestSource = 'none';
+    var bestSignature = 'none';
+    for (var j = 0; j < pool.length; j++) {
+      var pick = pool[j];
+      if (pick.score > bestScore || (pick.score === bestScore && pick.area > bestArea)) {
+        bestScore = pick.score;
+        bestArea = pick.area;
+        best = pick.canvas;
+        bestIndex = pick.index;
+        bestSource = pick.source;
+        bestSignature = pick.signature;
       }
     }
     if (!best) {
       return null;
     }
     var out = {
       canvasCount: candidates.length,
+      canvasConsidered: evaluated.length,
+      canvasLargeCount: pool.length,
+      canvasMinLargeArea: minLargeArea,
       canvasPick: bestIndex,
       canvasArea: bestArea,
       canvasScore: bestScore,
@@ -677,6 +711,9 @@
       }
       global.__cn1LastScreenshotSignature = result.canvasSignature || '';
       diag('SCREENSHOT_START', 'canvasCount', result.canvasCount);
+      diag('SCREENSHOT_START', 'canvasConsidered', result.canvasConsidered | 0);
+      diag('SCREENSHOT_START', 'canvasLargeCount', result.canvasLargeCount | 0);
+      diag('SCREENSHOT_START', 'canvasMinLargeArea', result.canvasMinLargeArea | 0);
       diag('SCREENSHOT_START', 'canvasPick', result.canvasPick);
       diag('SCREENSHOT_START', 'canvasArea', result.canvasArea);
       diag('SCREENSHOT_START', 'canvasScore', result.canvasScore);