SDL: Add SDL_MOUSE_RELATIVE_CURSOR_VISIBLE (#7947)

From ee559d51bed864968e529d4e63e2019d9de72291 Mon Sep 17 00:00:00 2001
From: expikr <[EMAIL REDACTED]>
Date: Sun, 16 Jun 2024 06:21:29 -0700
Subject: [PATCH] Add SDL_MOUSE_RELATIVE_CURSOR_VISIBLE (#7947)

---
 include/SDL3/SDL_hints.h | 11 +++++++++++
 src/events/SDL_mouse.c   | 15 ++++++++++++++-
 src/events/SDL_mouse_c.h |  1 +
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/include/SDL3/SDL_hints.h b/include/SDL3/SDL_hints.h
index 8b8ba6cf33eb0..3f39e009313cb 100644
--- a/include/SDL3/SDL_hints.h
+++ b/include/SDL3/SDL_hints.h
@@ -2289,6 +2289,17 @@ extern "C" {
  */
 #define SDL_HINT_MOUSE_RELATIVE_WARP_MOTION  "SDL_MOUSE_RELATIVE_WARP_MOTION"
 
+/**
+ *  \brief  A variable controlling whether the hardware cursor stays visible when relative mode is active.
+ *
+ *  This variable can be set to the following values:
+ *    "0"       - The cursor will be hidden while relative mode is active (default)
+ *    "1"       - The cursor will remain visible while relative mode is active
+ *
+ *  Note that for systems without raw hardware inputs, relative mode is implemented using warping, so the hardware cursor will visibly warp between frames if this is enabled on those systems.
+ */
+#define SDL_HINT_MOUSE_RELATIVE_CURSOR_VISIBLE  "SDL_MOUSE_RELATIVE_CURSOR_VISIBLE"
+
 /**
  * A variable controlling whether mouse events should generate synthetic touch
  * events.
diff --git a/src/events/SDL_mouse.c b/src/events/SDL_mouse.c
index 476959eccc53c..29fe106d87263 100644
--- a/src/events/SDL_mouse.c
+++ b/src/events/SDL_mouse.c
@@ -171,6 +171,13 @@ static void SDLCALL SDL_MouseRelativeWarpMotionChanged(void *userdata, const cha
     mouse->relative_mode_warp_motion = SDL_GetStringBoolean(hint, SDL_FALSE);
 }
 
+static void SDLCALL SDL_MouseRelativeCursorVisibleChanged(void *userdata, const char *name, const char *oldValue, const char *hint)
+{
+    SDL_Mouse *mouse = (SDL_Mouse *)userdata;
+
+    mouse->relative_mode_cursor_visible = SDL_GetStringBoolean(hint, SDL_FALSE);
+}
+
 /* Public functions */
 int SDL_PreInitMouse(void)
 {
@@ -210,6 +217,9 @@ int SDL_PreInitMouse(void)
     SDL_AddHintCallback(SDL_HINT_MOUSE_RELATIVE_WARP_MOTION,
                         SDL_MouseRelativeWarpMotionChanged, mouse);
 
+    SDL_AddHintCallback(SDL_HINT_MOUSE_RELATIVE_CURSOR_VISIBLE,
+                        SDL_MouseRelativeCursorVisibleChanged, mouse);
+
     mouse->was_touch_mouse_events = SDL_FALSE; /* no touch to mouse movement event pending */
 
     mouse->cursor_shown = SDL_TRUE;
@@ -1119,6 +1129,9 @@ void SDL_QuitMouse(void)
 
     SDL_DelHintCallback(SDL_HINT_MOUSE_RELATIVE_WARP_MOTION,
                         SDL_MouseRelativeWarpMotionChanged, mouse);
+    
+    SDL_DelHintCallback(SDL_HINT_MOUSE_RELATIVE_CURSOR_VISIBLE,
+                        SDL_MouseRelativeCursorVisibleChanged, mouse);
 
     for (int i = SDL_mouse_count; i--; ) {
         SDL_RemoveMouse(SDL_mice[i].instance_id, SDL_FALSE);
@@ -1541,7 +1554,7 @@ int SDL_SetCursor(SDL_Cursor *cursor)
         }
     }
 
-    if (cursor && (!mouse->focus || (mouse->cursor_shown && !mouse->relative_mode))) {
+    if (cursor && (!mouse->focus || (mouse->cursor_shown && (mouse->relative_mode_cursor_visible || !mouse->relative_mode) ) ) ) {
         if (mouse->ShowCursor) {
             mouse->ShowCursor(cursor);
         }
diff --git a/src/events/SDL_mouse_c.h b/src/events/SDL_mouse_c.h
index b2f4d25df2ee5..6d120ec3ecb03 100644
--- a/src/events/SDL_mouse_c.h
+++ b/src/events/SDL_mouse_c.h
@@ -91,6 +91,7 @@ typedef struct
     SDL_bool relative_mode;
     SDL_bool relative_mode_warp;
     SDL_bool relative_mode_warp_motion;
+    SDL_bool relative_mode_cursor_visible;
     SDL_bool enable_normal_speed_scale;
     float normal_speed_scale;
     SDL_bool enable_relative_speed_scale;