Check that the framebuffer image matches expectations

src/Backends/Rendering/Window/Software/X11.cpp

@@ -31,6 +31,14 @@ static bool CheckShm() {
     return exists;
 }
 
+bool checkImageOK(XImage* image) {
+    bool ok = true;
+    ok &= (image->width == screenWidth);
+    ok &= (image->bytes_per_line == screenWidth * 4);
+    ok &= (image->depth == 24 || image->depth == 32);
+    return ok;
+}
+
 void createFramebuffer() {
     gc = DefaultGC(xDisplay, DefaultScreen(xDisplay));
 
@@ -83,10 +91,15 @@ bool WindowBackend_Software_CreateWindow(const char *window_title, size_t screen
     XSetWMProtocols(xDisplay, window, &WM_DELETE_WINDOW, 1);
 
     createFramebuffer();
+    if(checkImageOK(framebufferImage) == false) {
+        Backend_PrintError("Something's off with the framebuffer.\n");
+        return false;
+    }
 
     if(framebufferImage == 0) {
         return false;
     }
+
     framebufferPitch = screen_width * 4;
     return true;
 }