From 760550ca0d19ecba0ad1ec0fd0cfb4d8655c63f5 Mon Sep 17 00:00:00 2001
From: Lovell Fuller <github@lovell.info>
Date: Thu, 4 Jun 2020 20:29:02 +0100
Subject: [PATCH] Expose levels metadata for multi-level images #2222

---
 docs/api-input.md |  1 +
 docs/changelog.md |  3 +++
 lib/input.js      |  1 +
 src/metadata.cc   | 20 ++++++++++++++++++++
 src/metadata.h    |  1 +
 5 files changed, 26 insertions(+)

diff --git a/docs/api-input.md b/docs/api-input.md
index 6f1c6bde..2ab3416f 100644
--- a/docs/api-input.md
+++ b/docs/api-input.md
@@ -20,6 +20,7 @@ A `Promise` is returned when `callback` is not provided.
 -   `loop`: Number of times to loop an animated image, zero refers to a continuous loop.
 -   `delay`: Delay in ms between each page in an animated image, provided as an array of integers.
 -   `pagePrimary`: Number of the primary page in a HEIF image
+-   `levels`: Details of each level in a multi-level image provided as an array of objects, requires libvips compiled with support for OpenSlide
 -   `hasProfile`: Boolean indicating the presence of an embedded ICC profile
 -   `hasAlpha`: Boolean indicating the presence of an alpha transparency channel
 -   `orientation`: Number value of the EXIF Orientation header, if present
diff --git a/docs/changelog.md b/docs/changelog.md
index a09c67d0..27cf1b0b 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -14,6 +14,9 @@ Requires libvips v8.9.1
   [#2226](https://github.com/lovell/sharp/pull/2226)
   [@romaleev](https://github.com/romaleev)
 
+* Expose `levels` metadata for multi-level images.
+  [#2222](https://github.com/lovell/sharp/issues/2222)
+
 ### v0.25.3 - 17th May 2020
 
 * Ensure libvips is initialised only once, improves worker thread safety.
diff --git a/lib/input.js b/lib/input.js
index c389d29d..0abf64c3 100644
--- a/lib/input.js
+++ b/lib/input.js
@@ -208,6 +208,7 @@ function _isStreamInput () {
  * - `loop`: Number of times to loop an animated image, zero refers to a continuous loop.
  * - `delay`: Delay in ms between each page in an animated image, provided as an array of integers.
  * - `pagePrimary`: Number of the primary page in a HEIF image
+ * - `levels`: Details of each level in a multi-level image provided as an array of objects, requires libvips compiled with support for OpenSlide
  * - `hasProfile`: Boolean indicating the presence of an embedded ICC profile
  * - `hasAlpha`: Boolean indicating the presence of an alpha transparency channel
  * - `orientation`: Number value of the EXIF Orientation header, if present
diff --git a/src/metadata.cc b/src/metadata.cc
index 25c2871c..34d0e4bc 100644
--- a/src/metadata.cc
+++ b/src/metadata.cc
@@ -74,6 +74,15 @@ class MetadataWorker : public Napi::AsyncWorker {
       if (image.get_typeof("heif-primary") == G_TYPE_INT) {
         baton->pagePrimary = image.get_int("heif-primary");
       }
+      if (image.get_typeof("openslide.level-count") == VIPS_TYPE_REF_STRING) {
+        int const levels = std::stoi(image.get_string("openslide.level-count"));
+        for (int l = 0; l < levels; l++) {
+          std::string prefix = "openslide.level[" + std::to_string(l) + "].";
+          int const width = std::stoi(image.get_string((prefix + "width").data()));
+          int const height = std::stoi(image.get_string((prefix + "height").data()));
+          baton->levels.push_back(std::pair<int, int>(width, height));
+        }
+      }
       baton->hasProfile = sharp::HasProfile(image);
       // Derived attributes
       baton->hasAlpha = sharp::HasAlpha(image);
@@ -177,6 +186,17 @@ class MetadataWorker : public Napi::AsyncWorker {
       if (baton->pagePrimary > -1) {
         info.Set("pagePrimary", baton->pagePrimary);
       }
+      if (!baton->levels.empty()) {
+        int i = 0;
+        Napi::Array levels = Napi::Array::New(env, static_cast<size_t>(baton->levels.size()));
+        for (std::pair<int, int> const l : baton->levels) {
+          Napi::Object level = Napi::Object::New(env);
+          level.Set("width", l.first);
+          level.Set("height", l.second);
+          levels.Set(i++, level);
+        }
+        info.Set("levels", levels);
+      }
       info.Set("hasProfile", baton->hasProfile);
       info.Set("hasAlpha", baton->hasAlpha);
       if (baton->orientation > 0) {
diff --git a/src/metadata.h b/src/metadata.h
index abb860fb..00553085 100644
--- a/src/metadata.h
+++ b/src/metadata.h
@@ -39,6 +39,7 @@ struct MetadataBaton {
   int loop;
   std::vector<int> delay;
   int pagePrimary;
+  std::vector<std::pair<int, int>> levels;
   bool hasProfile;
   bool hasAlpha;
   int orientation;