fix: convert physical pixels to CSS pixels before passing to windows webview

Author: MeronNagy

v3/UNRELEASED_CHANGELOG.md

@@ -25,6 +25,7 @@ After processing, the content will be moved to the main changelog and this file
 ## Fixed
 - Fixed linux desktop.tmpl protocol range, by removing `<.Info.Protocol>` to `<.Protocol>` by @Tolfx in #4510
 - Fixed redefinition error for liquid glass demo in [#4542](https://github.com/wailsapp/wails/pull/4542) by @Etesam913
+- Fixed DnD dropzone detection failing at non-100% display scaling on Windows [#4632](https://github.com/wailsapp/wails/pull/4632) by @yulesxoxo
 
 ## Deprecated
 <!-- Soon-to-be removed features -->

v3/internal/runtime/desktop/@wailsio/runtime/src/window.ts

@@ -539,8 +539,8 @@ class Window {
      * Gathers information about the drop target element and sends it back to the Go backend.
      *
      * @param filenames - An array of file paths (strings) that were dropped.
-     * @param x - The x-coordinate of the drop event.
-     * @param y - The y-coordinate of the drop event.
+     * @param x - The x-coordinate of the drop event, in logical (CSS) pixels relative to the webview.
+     * @param y - The y-coordinate of the drop event, in logical (CSS) pixels relative to the webview.
      */
     HandlePlatformFileDrop(filenames: string[], x: number, y: number): void {
         const element = document.elementFromPoint(x, y);

v3/pkg/application/webview_window_windows.go

@@ -5,6 +5,7 @@ package application
 import (
 	"errors"
 	"fmt"
+	"math"
 	"net/url"
 	"strconv"
 	"strings"
@@ -605,12 +606,25 @@ func (w *windowsWebviewWindow) convertWindowToWebviewCoordinates(windowX, window
 	globalApplication.debug("[DragDropDebug] convertWindowToWebviewCoordinates: Calculated offset", "offsetX", offsetX, "offsetY", offsetY)
 
 	// Convert window-relative coordinates to webview-relative coordinates
-	webviewX := windowX - offsetX
-	webviewY := windowY - offsetY
+	webviewPhysicalX := windowX - offsetX
+	webviewPhysicalY := windowY - offsetY
 
-	globalApplication.debug("[DragDropDebug] convertWindowToWebviewCoordinates: Final webview coordinates", "webviewX", webviewX, "webviewY", webviewY)
+	globalApplication.debug("[DragDropDebug] convertWindowToWebviewCoordinates: Webview coordinates before DPI Scaling", "webviewPhysicalX", webviewPhysicalX, "webviewPhysicalY", webviewPhysicalY)
 
-	return webviewX, webviewY
+	// Get DPI for this window
+	dpi := w32.GetDpiForWindow(w.hwnd)
+	// Convert to scale factor: 96 DPI == 1.0 (100%)
+	scaleFactor := float64(dpi) / 96.0
+	globalApplication.debug("[DragDropDebug] convertWindowToWebviewCoordinates: DPI info", "dpi", dpi, "scaleFactor", scaleFactor)
+
+	// Convert physical pixels -> logical/CSS pixels by dividing by the scale factor
+	// Use rounding to avoid truncation artefacts
+	webviewLogicalX := int(math.Round(float64(webviewPhysicalX) / scaleFactor))
+	webviewLogicalY := int(math.Round(float64(webviewPhysicalY) / scaleFactor))
+	globalApplication.debug("[DragDropDebug] convertWindowToWebviewCoordinates: Final webview coordinates (logical/CSS pixels)",
+		"webviewLogicalX", webviewLogicalX, "webviewLogicalY", webviewLogicalY)
+
+	return webviewLogicalX, webviewLogicalY
 }
 
 func (w *windowsWebviewWindow) physicalBounds() Rect {