From 3a96977ea85975571141c5c29c1c1bb684a6f7c6 Mon Sep 17 00:00:00 2001
From: Jani Pehkonen <janpe2@users.noreply.github.com>
Date: Wed, 14 Apr 2021 14:58:43 +0300
Subject: [PATCH] Implement visibility expressions for optional content

---
 src/core/evaluator.js                  |  57 ++++++++++++++++++++++---
 src/display/optional_content_config.js |  42 ++++++++++++++++--
 test/pdfs/.gitignore                   |   1 +
 test/pdfs/visibility_expressions.pdf   | Bin 0 -> 3921 bytes
 test/test_manifest.json                |   6 +++
 5 files changed, 96 insertions(+), 10 deletions(-)
 create mode 100644 test/pdfs/visibility_expressions.pdf

diff --git a/src/core/evaluator.js b/src/core/evaluator.js
index 3c49f9783..f0f2af3a6 100644
--- a/src/core/evaluator.js
+++ b/src/core/evaluator.js
@@ -1306,6 +1306,43 @@ class PartialEvaluator {
     throw new FormatError(`Unknown PatternName: ${patternName}`);
   }
 
+  _parseVisibilityExpression(array, nestingCounter, currentResult) {
+    const MAX_NESTING = 10;
+    if (++nestingCounter > MAX_NESTING) {
+      warn("Visibility expression is too deeply nested");
+      return;
+    }
+    const length = array.length;
+    const operator = this.xref.fetchIfRef(array[0]);
+    if (length < 2 || !isName(operator)) {
+      warn("Invalid visibility expression");
+      return;
+    }
+    switch (operator.name) {
+      case "And":
+      case "Or":
+      case "Not":
+        currentResult.push(operator.name);
+        break;
+      default:
+        warn(`Invalid operator ${operator.name} in visibility expression`);
+        return;
+    }
+    for (let i = 1; i < length; i++) {
+      const raw = array[i];
+      const object = this.xref.fetchIfRef(raw);
+      if (Array.isArray(object)) {
+        const nestedResult = [];
+        currentResult.push(nestedResult);
+        // Recursively parse a subarray.
+        this._parseVisibilityExpression(object, nestingCounter, nestedResult);
+      } else if (isRef(raw)) {
+        // Reference to an OCG dictionary.
+        currentResult.push(raw.toString());
+      }
+    }
+  }
+
   async parseMarkedContentProps(contentProperties, resources) {
     let optionalContent;
     if (isName(contentProperties)) {
@@ -1324,6 +1361,18 @@ class PartialEvaluator {
         id: optionalContent.objId,
       };
     } else if (optionalContentType === "OCMD") {
+      const expression = optionalContent.get("VE");
+      if (Array.isArray(expression)) {
+        const result = [];
+        this._parseVisibilityExpression(expression, 0, result);
+        if (result.length > 0) {
+          return {
+            type: "OCMD",
+            expression: result,
+          };
+        }
+      }
+
       const optionalContentGroups = optionalContent.get("OCGs");
       if (
         Array.isArray(optionalContentGroups) ||
@@ -1339,19 +1388,13 @@ class PartialEvaluator {
           groupIds.push(optionalContentGroups.objId);
         }
 
-        let expression = null;
-        if (optionalContent.get("VE")) {
-          // TODO support visibility expression.
-          expression = true;
-        }
-
         return {
           type: optionalContentType,
           ids: groupIds,
           policy: isName(optionalContent.get("P"))
             ? optionalContent.get("P").name
             : null,
-          expression,
+          expression: null,
         };
       } else if (isRef(optionalContentGroups)) {
         return {
diff --git a/src/display/optional_content_config.js b/src/display/optional_content_config.js
index 7d1f3178e..424c3a5c6 100644
--- a/src/display/optional_content_config.js
+++ b/src/display/optional_content_config.js
@@ -57,6 +57,43 @@ class OptionalContentConfig {
     }
   }
 
+  _evaluateVisibilityExpression(array) {
+    const length = array.length;
+    if (length < 2) {
+      return true;
+    }
+    const operator = array[0];
+    for (let i = 1; i < length; i++) {
+      const element = array[i];
+      let state;
+      if (Array.isArray(element)) {
+        state = this._evaluateVisibilityExpression(element);
+      } else if (this._groups.has(element)) {
+        state = this._groups.get(element).visible;
+      } else {
+        warn(`Optional content group not found: ${element}`);
+        return true;
+      }
+      switch (operator) {
+        case "And":
+          if (!state) {
+            return false;
+          }
+          break;
+        case "Or":
+          if (state) {
+            return true;
+          }
+          break;
+        case "Not":
+          return !state;
+        default:
+          return true;
+      }
+    }
+    return operator === "And";
+  }
+
   isVisible(group) {
     if (group.type === "OCG") {
       if (!this._groups.has(group.id)) {
@@ -65,10 +102,9 @@ class OptionalContentConfig {
       }
       return this._groups.get(group.id).visible;
     } else if (group.type === "OCMD") {
-      // Per the spec, the expression should be preferred if available. Until
-      // we implement this, just fallback to using the group policy for now.
+      // Per the spec, the expression should be preferred if available.
       if (group.expression) {
-        warn("Visibility expression not supported yet.");
+        return this._evaluateVisibilityExpression(group.expression);
       }
       if (!group.policy || group.policy === "AnyOn") {
         // Default
diff --git a/test/pdfs/.gitignore b/test/pdfs/.gitignore
index f74d3ead8..0de249e8c 100644
--- a/test/pdfs/.gitignore
+++ b/test/pdfs/.gitignore
@@ -354,6 +354,7 @@
 !issue2128r.pdf
 !issue5540.pdf
 !issue5549.pdf
+!visibility_expressions.pdf
 !issue5475.pdf
 !issue10519_reduced.pdf
 !annotation-border-styles.pdf
diff --git a/test/pdfs/visibility_expressions.pdf b/test/pdfs/visibility_expressions.pdf
new file mode 100644
index 0000000000000000000000000000000000000000..e4418910d56d80b58081a7c8ecb1b01e64edd27c
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diff --git a/test/test_manifest.json b/test/test_manifest.json
index c9a8fe4ba..575ebc8bb 100644
--- a/test/test_manifest.json
+++ b/test/test_manifest.json
@@ -2635,6 +2635,12 @@
        "link": false,
        "type": "eq"
     },
+    {  "id": "visibility_expressions",
+       "file": "pdfs/visibility_expressions.pdf",
+       "md5": "bc530d90984ddaa2cc7e0cd53fc2cf34",
+       "rounds": 1,
+       "type": "eq"
+   },
     {  "id": "issue7580-text",
        "file": "pdfs/issue7580.pdf",
        "md5": "44dd5a9b4373fcab9890cf567722a766",