REGRESSION: Thumbnail turns blank after choose A3/Tabloid paper size …

…in Print Screen

https://bugs.webkit.org/show_bug.cgi?id=255210
rdar://107503946

Reviewed by Wenson Hsieh.

iOS print preview thumbnail generation uses `CGBitmapContextCreateImage` to create the bitmap image.
However, with some combinations of page scale size with paper size, the resulting image dimension
becomes too large, resulting in the function returning null and no thumbnail being generated.

This PR fixes this by scaling down the dimensions before the image is created to ensure the maximum
possible size of the image is constrained. This limit is the size at which the thumbnail itself is
rendered, so the scaling is safe to do.

* Source/WebKit/WebProcess/WebPage/ios/WebPageIOS.mm:
(WebKit::WebPage::drawToImage):

Canonical link: https://commits.webkit.org/262780@main

Source/WebKit/WebProcess/WebPage/ios/WebPageIOS.mm

@@ -4503,6 +4503,17 @@ static bool selectionIsInsideFixedPositionContainer(LocalFrame& frame)
     Checked<int> pageWidth = pageRects[0].width();
     Checked<int> pageHeight = pageRects[0].height();
 
+    // The thumbnail images are always a maximum of 500 x 500.
+    static constexpr float maximumPrintPreviewDimensionSize = 500.0;
+
+    // If the sizes are too large, the bitmap will not be able to be created,
+    // so scale them down.
+    float scaleFactor = maximumPrintPreviewDimensionSize / static_cast<int>(std::max(pageWidth, pageHeight));
+    if (scaleFactor < 1.0) {
+        pageWidth = static_cast<int>(std::floorf(static_cast<int>(pageWidth) * scaleFactor));
+        pageHeight = static_cast<int>(std::floorf(static_cast<int>(pageHeight) * scaleFactor));
+    }
+
     int imageHeight;
     if (!WTF::safeMultiply(pageHeight.value<size_t>(), pageCount, imageHeight)) {
         reply({ });