From 2c93c071d1142203e1efc6c5ff348c7357d02ce1 Mon Sep 17 00:00:00 2001
From: John Lorentzson <duuqnd@stacken.kth.se>
Date: Wed, 9 Apr 2025 14:54:13 +0200
Subject: [PATCH] Add use of XShm for faster transfer speeds between game and X
 server

---
 CMakeLists.txt                                |  2 +-
 .../Rendering/Window/Software/X11.cpp         | 76 ++++++++++++++-----
 2 files changed, 59 insertions(+), 19 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 98c27ba6..32d3c5df 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -572,7 +572,7 @@ if(BACKEND_PLATFORM MATCHES "GLFW3")
 endif()
 
 if(BACKEND_PLATFORM MATCHES "X11")
-    target_link_libraries(CSE2 PRIVATE "-lX11")
+    target_link_libraries(CSE2 PRIVATE "-lXext -lX11")
 endif()
 
 if(BACKEND_PLATFORM MATCHES "SDL2" OR BACKEND_AUDIO MATCHES "SDL2")
diff --git a/src/Backends/Rendering/Window/Software/X11.cpp b/src/Backends/Rendering/Window/Software/X11.cpp
index 208848e7..e97b887e 100644
--- a/src/Backends/Rendering/Window/Software/X11.cpp
+++ b/src/Backends/Rendering/Window/Software/X11.cpp
@@ -8,19 +8,55 @@
 
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+#include <X11/extensions/XShm.h>
 
 static Window window;
 static XImage* framebufferImage;
 static unsigned char* framebufferPixels;
 static int framebufferPitch;
-static unsigned char* xfriendlyFB;
+static char* xfriendlyFB;
 static GC gc;
 static int screenWidth;
 static int screenHeight;
-static Pixmap intermediate;
+static bool useShmP = false;
+static XShmSegmentInfo seginfo;
+
 extern Display* xDisplay;
 extern Visual* xVisual;
 
+static bool CheckShm() {
+    bool exists = XShmQueryExtension(xDisplay);
+    return exists;
+}
+
+void createFramebuffer() {
+    gc = DefaultGC(xDisplay, DefaultScreen(xDisplay));
+
+    int depth = DefaultDepth(xDisplay, DefaultScreen(xDisplay));
+
+    // Setting up the framebuffer
+    xfriendlyFB = NULL;
+
+    if(useShmP) {
+        framebufferImage = XShmCreateImage(xDisplay, xVisual,
+                                           depth, ZPixmap, NULL,
+                                           &seginfo, screenWidth, screenHeight);
+        seginfo.shmid = shmget(IPC_PRIVATE,
+                               framebufferImage->bytes_per_line * framebufferImage->height,
+                               IPC_CREAT | 0777);
+        seginfo.shmaddr = xfriendlyFB = framebufferImage->data = (char*)shmat(seginfo.shmid, NULL, 0);
+        XShmAttach(xDisplay, &seginfo);
+    } else {
+        xfriendlyFB = (char*)malloc(screenWidth * screenHeight * 4);
+        framebufferImage = XCreateImage(xDisplay, xVisual,
+                                        depth, ZPixmap, 0,
+                                        (char*)xfriendlyFB, screenWidth, screenHeight,
+                                        32, 0);
+    }
+}
+
 bool WindowBackend_Software_CreateWindow(const char *window_title, size_t screen_width, size_t screen_height, bool fullscreen) {
     screenWidth = screen_width;
     screenHeight = screen_height;
@@ -28,8 +64,14 @@ bool WindowBackend_Software_CreateWindow(const char *window_title, size_t screen
     int screen = DefaultScreen(xDisplay);
     Window rootWindow = RootWindow(xDisplay, screen);
 
+    useShmP = CheckShm();
+    if(useShmP) {
+        Backend_PrintInfo("Using X shared memory extension for higher image transfer speeds.\n");
+    } else {
+        Backend_PrintInfo("Unable to use X shared memory extension. Expect lower performance.\n");
+    }
+
     window = XCreateWindow(xDisplay, rootWindow, 0, 0, screen_width, screen_height, 0, 24, InputOutput, xVisual, 0, NULL);
-    //window = XCreateSimpleWindow(xDisplay, rootWindow, 0, 0, screen_width, screen_height, 1, 0, 0);
     XSelectInput(xDisplay, window, ExposureMask | KeyPressMask | KeyReleaseMask);
     XMapRaised(xDisplay, window);
     XStoreName(xDisplay, window, window_title);
@@ -39,20 +81,8 @@ bool WindowBackend_Software_CreateWindow(const char *window_title, size_t screen
     Atom WM_DELETE_WINDOW = XInternAtom(xDisplay, "WM_DELETE_WINDOW", false);
     XSetWMProtocols(xDisplay, window, &WM_DELETE_WINDOW, 1);
 
-    gc = DefaultGC(xDisplay, DefaultScreen(xDisplay));
+    createFramebuffer();
 
-    int depth = DefaultDepth(xDisplay, DefaultScreen(xDisplay));
-
-    intermediate = XCreatePixmap(xDisplay, window, screenWidth, screenHeight, depth);
-
-    // Setting up the framebuffer
-    framebufferPixels = (unsigned char*)malloc(screen_width * screen_height * 4);
-    //xfriendlyFB = (unsigned char*)malloc(screen_width * screen_height * 4);
-    xfriendlyFB = framebufferPixels;
-    framebufferImage = XCreateImage(xDisplay, xVisual,//DefaultVisual(xDisplay, DefaultScreen(xDisplay)),
-                                    depth, ZPixmap, 0,
-                                    (char*)xfriendlyFB, screen_width, screen_height,
-                                    32, 0);
     if(framebufferImage == 0) {
         return false;
     }
@@ -64,10 +94,16 @@ unsigned char* WindowBackend_Software_GetFramebuffer(size_t *pitch)
 {
 	*pitch = framebufferPitch;
 
-	return (unsigned char*)framebufferPixels;
+	return (unsigned char*)xfriendlyFB;
 }
 
 void WindowBackend_Software_DestroyWindow(void) {
+    if(useShmP) {
+        XShmDetach(xDisplay, &seginfo);
+        XDestroyImage(framebufferImage);
+        shmdt(seginfo.shmaddr);
+        shmctl(seginfo.shmid, IPC_RMID, 0);
+    }
     XDestroyWindow(xDisplay, window);
 }
 
@@ -92,5 +128,9 @@ void WindowBackend_Software_Display(void) {
     //     srci += 4;
     // }
     //memcpy(xfriendlyFB, framebufferPixels, screenWidth * screenHeight * 4);
-    XPutImage(xDisplay, window, gc, framebufferImage, 0, 0, 0, 0, screenWidth, screenHeight);
+    if(useShmP) {
+        XShmPutImage(xDisplay, window, gc, framebufferImage, 0, 0, 0, 0, screenWidth, screenHeight, 0);
+    } else {
+        XPutImage(xDisplay, window, gc, framebufferImage, 0, 0, 0, 0, screenWidth, screenHeight);
+    }
 }