Simplify thumbnail resizing logic to ensure target constraints are respected (#28012)

Automatic Merge

server/channels/app/imaging/preview.go

@@ -26,32 +26,15 @@ func GeneratePreview(img image.Image, width int) image.Image {
 
 // GenerateThumbnail generates the thumbnail for the given image.
 func GenerateThumbnail(img image.Image, targetWidth, targetHeight int) image.Image {
-	thumb := img
 	width := img.Bounds().Dx()
 	height := img.Bounds().Dy()
-	expectedRatio := float64(targetHeight) / float64(targetWidth)
 
-	// If both dimensions are over the target size, we scale down until one is not.
-	// If one dimension is over the target size, we scale down until both are not.
-	// If neither dimension is over the target size, we return the image as is.
-	if height > targetHeight || width > targetWidth {
-		ratio := float64(height) / float64(width)
-		if ratio < expectedRatio {
-			if height >= targetHeight {
-				thumb = imaging.Resize(img, 0, targetHeight, imaging.Lanczos)
-			} else {
-				thumb = imaging.Resize(img, targetWidth, 0, imaging.Lanczos)
-			}
-		} else {
-			if width >= targetWidth {
-				thumb = imaging.Resize(img, targetWidth, 0, imaging.Lanczos)
-			} else {
-				thumb = imaging.Resize(img, 0, targetHeight, imaging.Lanczos)
-			}
-		}
+	// We keep aspect ratio and ensure the output dimensions are never higher than the provided targets.
+	if width > height {
+		return imaging.Resize(img, targetWidth, 0, imaging.Lanczos)
 	}
 
-	return thumb
+	return imaging.Resize(img, 0, targetHeight, imaging.Lanczos)
 }
 
 // GenerateMiniPreviewImage generates the mini preview for the given image.