SDL: cocoa: Warp mouse to center of window before enabling relative mouse. (125e7)

SDL Commits
1 
From 125e7420ecd2b0d1847aef804f53e614fbc68253 Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Sun, 11 Jun 2023 12:43:47 -0400
Subject: [PATCH] cocoa: Warp mouse to center of window before enabling
 relative mouse.

This prevents the case where the mouse might be at the edge of the
window when enabling relative mode, which confuses macOS, at it
might believe the user is attempting to resize the window.

Fixes #6994.

(cherry picked from commit 2afb49ba9a2edc361a3b35d8e30be977a5bcc0c4)
---
 src/video/cocoa/SDL_cocoamouse.m | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/video/cocoa/SDL_cocoamouse.m b/src/video/cocoa/SDL_cocoamouse.m
index 2dd4c1912291..a81f0fda8a71 100644
--- a/src/video/cocoa/SDL_cocoamouse.m
+++ b/src/video/cocoa/SDL_cocoamouse.m
@@ -296,10 +296,16 @@ static int Cocoa_WarpMouse(SDL_Window *window, float x, float y)
 
 static int Cocoa_SetRelativeMouseMode(SDL_bool enabled)
 {
+    SDL_Window *window = SDL_GetKeyboardFocus();
     CGError result;
-    SDL_Window *window;
     SDL_CocoaWindowData *data;
     if (enabled) {
+        if (window) {
+            /* make sure the mouse isn't at the corner of the window, as this can confuse things if macOS thinks a window resize is happening on the first click. */
+            const CGPoint point = CGPointMake((float)(window->x + (window->w / 2)), (float)(window->y + (window->h / 2)));
+            Cocoa_HandleMouseWarp(point.x, point.y);
+            CGWarpMouseCursorPosition(point);
+        }
         DLog("Turning on.");
         result = CGAssociateMouseAndMouseCursorPosition(NO);
     } else {
@@ -313,7 +319,6 @@ static int Cocoa_SetRelativeMouseMode(SDL_bool enabled)
     /* We will re-apply the non-relative mode when the window gets focus, if it
      * doesn't have focus right now.
      */
-    window = SDL_GetKeyboardFocus();
     if (!window) {
         return 0;
     }