Estimate size of images to avoid layout shifts (#5192)

src/messages/Image.cpp

@@ -318,7 +318,7 @@ Image::~Image()
     }
 }
 
-ImagePtr Image::fromUrl(const Url &url, qreal scale)
+ImagePtr Image::fromUrl(const Url &url, qreal scale, QSize expectedSize)
 {
     static std::unordered_map<Url, std::weak_ptr<Image>> cache;
     static std::mutex mutex;
@@ -329,7 +329,7 @@ ImagePtr Image::fromUrl(const Url &url, qreal scale)
 
     if (!shared)
     {
-        cache[url] = shared = ImagePtr(new Image(url, scale));
+        cache[url] = shared = ImagePtr(new Image(url, scale, expectedSize));
     }
 
     return shared;
@@ -382,9 +382,11 @@ Image::Image()
 {
 }
 
-Image::Image(const Url &url, qreal scale)
+Image::Image(const Url &url, qreal scale, QSize expectedSize)
     : url_(url)
     , scale_(scale)
+    , expectedSize_(expectedSize.isValid() ? expectedSize
+                                           : (QSize(16, 16) * scale))
     , shouldLoad_(true)
     , frames_(std::make_unique<detail::Frames>())
 {
@@ -477,11 +479,11 @@ int Image::width() const
 
     if (auto pixmap = this->frames_->first())
     {
-        return int(pixmap->width() * this->scale_);
+        return static_cast<int>(pixmap->width() * this->scale_);
     }
 
-    // No frames loaded, use our default magic width 16
-    return 16;
+    // No frames loaded, use the expected size
+    return static_cast<int>(this->expectedSize_.width() * this->scale_);
 }
 
 int Image::height() const
@@ -490,11 +492,11 @@ int Image::height() const
 
     if (auto pixmap = this->frames_->first())
     {
-        return int(pixmap->height() * this->scale_);
+        return static_cast<int>(pixmap->height() * this->scale_);
     }
 
-    // No frames loaded, use our default magic height 16
-    return 16;
+    // No frames loaded, use the expected size
+    return static_cast<int>(this->expectedSize_.height() * this->scale_);
 }
 
 void Image::actuallyLoad()

src/messages/Image.hpp

@@ -73,7 +73,8 @@ public:
     Image(Image &&) = delete;
     Image &operator=(Image &&) = delete;
 
-    static ImagePtr fromUrl(const Url &url, qreal scale = 1);
+    static ImagePtr fromUrl(const Url &url, qreal scale = 1,
+                            QSize expectedSize = {});
     static ImagePtr fromResourcePixmap(const QPixmap &pixmap, qreal scale = 1);
     static ImagePtr getEmpty();
 
@@ -93,7 +94,7 @@ public:
 
 private:
     Image();
-    Image(const Url &url, qreal scale);
+    Image(const Url &url, qreal scale, QSize expectedSize);
     Image(qreal scale);
 
     void setPixmap(const QPixmap &pixmap);
@@ -102,12 +103,18 @@ private:
 
     const Url url_{};
     const qreal scale_{1};
+    /// @brief The expected size of this image once its loaded.
+    ///
+    /// This doesn't represent the actual size (it can be different) - it's
+    /// just an estimation and provided to avoid (large) layout shifts when
+    /// loading images.
+    const QSize expectedSize_{16, 16};
     std::atomic_bool empty_{false};
 
-    mutable std::chrono::time_point<std::chrono::steady_clock> lastUsed_;
-
     bool shouldLoad_{false};
 
+    mutable std::chrono::time_point<std::chrono::steady_clock> lastUsed_;
+
     // gui thread only
     std::unique_ptr<detail::Frames> frames_{};