From 2ce9f640ef432b2d955e97c3636e95eb0864f79e Mon Sep 17 00:00:00 2001
From: Patric Stout <truebrain@openttd.org>
Date: Sat, 3 Jun 2023 23:08:37 +0200
Subject: [PATCH] Fix: [SDL] unify the way X11 and Wayland handle mouse events

Basically, we drop RelativeMode completely, and use the same trick
as used by the Windows driver: read all motion events till the last
one, and use that as value.
---
 src/video/sdl2_v.cpp | 22 +++++++++++++++-------
 src/video/sdl_v.cpp  | 17 +++++++++++++++--
 2 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/src/video/sdl2_v.cpp b/src/video/sdl2_v.cpp
index 51c490d231..51271c2b30 100644
--- a/src/video/sdl2_v.cpp
+++ b/src/video/sdl2_v.cpp
@@ -371,12 +371,25 @@ bool VideoDriver_SDL_Base::PollEvent()
 	if (!SDL_PollEvent(&ev)) return false;
 
 	switch (ev.type) {
-		case SDL_MOUSEMOTION:
-			if (_cursor.UpdateCursorPosition(ev.motion.x, ev.motion.y, true)) {
+		case SDL_MOUSEMOTION: {
+			int32_t x = ev.motion.x;
+			int32_t y = ev.motion.y;
+
+			if (_cursor.fix_at) {
+				/* Get all queued mouse events now in case we have to warp the cursor. In the
+				 * end, we only care about the current mouse position and not bygone events. */
+				while (SDL_PeepEvents(&ev, 1, SDL_GETEVENT, SDL_MOUSEMOTION, SDL_MOUSEMOTION)) {
+					x = ev.motion.x;
+					y = ev.motion.y;
+				}
+			}
+
+			if (_cursor.UpdateCursorPosition(x, y, false)) {
 				SDL_WarpMouseInWindow(this->sdl_window, _cursor.pos.x, _cursor.pos.y);
 			}
 			HandleMouseEvents();
 			break;
+		}
 
 		case SDL_MOUSEWHEEL:
 			if (ev.wheel.y > 0) {
@@ -478,10 +491,8 @@ bool VideoDriver_SDL_Base::PollEvent()
 			} else if (ev.window.event == SDL_WINDOWEVENT_ENTER) {
 				// mouse entered the window, enable cursor
 				_cursor.in_window = true;
-#ifdef __EMSCRIPTEN__
 				/* Ensure pointer lock will not occur. */
 				SDL_SetRelativeMouseMode(SDL_FALSE);
-#endif
 			} else if (ev.window.event == SDL_WINDOWEVENT_LEAVE) {
 				// mouse left the window, undraw cursor
 				UndrawMouseCursor();
@@ -500,9 +511,6 @@ static const char *InitializeSDL()
 	 * UpdateWindowSurface() to update the window's texture instead of
 	 * its surface. */
 	SDL_SetHint(SDL_HINT_FRAMEBUFFER_ACCELERATION, "0");
-#ifndef __EMSCRIPTEN__
-	SDL_SetHint(SDL_HINT_MOUSE_RELATIVE_MODE_WARP, "1");
-#endif
 
 	/* Check if the video-driver is already initialized. */
 	if (SDL_WasInit(SDL_INIT_VIDEO) != 0) return nullptr;
diff --git a/src/video/sdl_v.cpp b/src/video/sdl_v.cpp
index 1b180d3b8b..d01b17e194 100644
--- a/src/video/sdl_v.cpp
+++ b/src/video/sdl_v.cpp
@@ -477,12 +477,25 @@ bool VideoDriver_SDL::PollEvent()
 	if (!SDL_PollEvent(&ev)) return false;
 
 	switch (ev.type) {
-		case SDL_MOUSEMOTION:
-			if (_cursor.UpdateCursorPosition(ev.motion.x, ev.motion.y, true)) {
+		case SDL_MOUSEMOTION: {
+			int32_t x = ev.motion.x;
+			int32_t y = ev.motion.y;
+
+			if (_cursor.fix_at) {
+				/* Get all queued mouse events now in case we have to warp the cursor. In the
+				 * end, we only care about the current mouse position and not bygone events. */
+				while (SDL_PeepEvents(&ev, 1, SDL_GETEVENT, SDL_MOUSEMOTION)) {
+					x = ev.motion.x;
+					y = ev.motion.y;
+				}
+			}
+
+			if (_cursor.UpdateCursorPosition(x, y, false)) {
 				SDL_WarpMouse(_cursor.pos.x, _cursor.pos.y);
 			}
 			HandleMouseEvents();
 			break;
+		}
 
 		case SDL_MOUSEBUTTONDOWN:
 			if (_rightclick_emulate && SDL_GetModState() & KMOD_CTRL) {