feat: expand Intel GPU display management

programs/include/gui/framebuffer.hpp

@@ -8,6 +8,7 @@
 #include <cstdint>
 #include <montauk/syscall.h>
 #include <montauk/string.h>
+#include <montauk/config.h>
 #include "gui/gui.hpp"
 
 namespace gui {
@@ -61,6 +62,20 @@ class Framebuffer {
         return 0xFF000000 | (rr << 16) | (gg << 8) | bb;
     }
 
+    static bool prefer_hardware_page_flip() {
+        char user[64] = {};
+        if (montauk::getuser(user, sizeof(user)) > 0 && user[0]) {
+            auto doc = montauk::config::load_user(user, "display");
+            bool enabled = doc.get_bool("graphics.tear_free", true);
+            doc.destroy();
+            return enabled;
+        }
+        auto doc = montauk::config::load("display");
+        bool enabled = doc.get_bool("graphics.tear_free", true);
+        doc.destroy();
+        return enabled;
+    }
+
 public:
     Framebuffer() : hw_fb(nullptr), hw_fb2(nullptr), back_buf(nullptr),
                     fb_width(0), fb_height(0), fb_pitch(0), hw_next(1) {
@@ -76,7 +91,8 @@ public:
 
         // Hardware page flipping: fb_map() maps the second scanout buffer
         // directly after the first when the kernel supports flipping.
-        if (hw_fb && montauk::fb_flip(-1, 0) == 1) {
+        if (hw_fb && prefer_hardware_page_flip()
+            && montauk::fb_flip(-1, 0) == 1) {
             uint64_t pages = ((uint64_t)fb_height * fb_pitch + 0xFFF) / 0x1000;
             hw_fb2 = (uint32_t*)((uint8_t*)hw_fb + pages * 0x1000);
         }