feat: render placeholders while waiting for images to render (#1003)

src/activities/reader/EpubReaderActivity.cpp

@@ -155,6 +155,8 @@ void EpubReaderActivity::onEnter() {
     return;
   }
 
+  ImageBlock::clearSessionRenderFailures();
+
   // Configure screen orientation based on settings
   // NOTE: This affects layout math and must be applied before any render calls.
   ReaderUtils::applyOrientation(renderer, SETTINGS.orientation);
@@ -1346,6 +1348,7 @@ void EpubReaderActivity::renderContents(std::unique_ptr<Page> page, const int or
   const auto tPrewarm = millis();
 
   const bool pageHasImages = page->hasImages();
+  const bool pageHasImagesNeedingDecode = pageHasImages && page->hasImagesNeedingDecode();
   const bool needsTextGrayscale = SETTINGS.textAntiAliasing;
   const bool needsAnyGrayscale = needsTextGrayscale || pageHasImages;
   auto renderGrayscalePass = [&]() {
@@ -1356,6 +1359,13 @@ void EpubReaderActivity::renderContents(std::unique_ptr<Page> page, const int or
     }
   };
 
+  if (pageHasImagesNeedingDecode) {
+    page->renderWithImagePlaceholders(renderer, fontId, orientedMarginLeft, orientedMarginTop);
+    renderStatusBar();
+    renderer.displayBuffer(HalDisplay::FAST_REFRESH);
+    renderer.clearScreen();
+  }
+
   page->render(renderer, fontId, orientedMarginLeft, orientedMarginTop);
   renderStatusBar();
   const auto tBwRender = millis();