From dd9473f096e8e718de6aefe772d9d0bf7eb1f73f Mon Sep 17 00:00:00 2001
From: Louis Kruger <louisk@gmail.com>
Date: Tue, 15 Oct 2019 16:18:38 -0400
Subject: [PATCH] test if renderer re-initialization is really necessary

---
 app/src/scrcpy.c |  6 ++++--
 app/src/screen.c | 28 ++++++++++++++++++++++++++--
 app/src/screen.h | 13 +++++++++++++
 3 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/app/src/scrcpy.c b/app/src/scrcpy.c
index cbf3a40ed0..cb4cfb36d9 100644
--- a/app/src/scrcpy.c
+++ b/app/src/scrcpy.c
@@ -146,8 +146,10 @@ handle_event(SDL_Event *event, bool control) {
             switch (event->window.event) {
                 case SDL_WINDOWEVENT_SIZE_CHANGED:
 #ifdef HIDPI_SUPPORT
-                    LOGD("Reinitializing renderer");
-                    screen_init_renderer_and_texture(&screen);
+                    if (!screen_test_correct_hidpi_ratio(&screen)) {
+                      LOGW("Reinitializing renderer due to incorrect hidpi ratio");
+                      screen_init_renderer_and_texture(&screen);
+                    }
 #endif
                     // fall-through no break
                 case SDL_WINDOWEVENT_EXPOSED:
diff --git a/app/src/screen.c b/app/src/screen.c
index 52035a8084..5e1be43a72 100644
--- a/app/src/screen.c
+++ b/app/src/screen.c
@@ -47,7 +47,10 @@ set_window_size(struct screen *screen, struct size new_size) {
     } else {
         SDL_SetWindowSize(screen->window, new_size.width, new_size.height);
 #ifdef HIDPI_SUPPORT
-        screen_init_renderer_and_texture(screen);
+        if (!screen_test_correct_hidpi_ratio(screen)) {
+            LOGW("Reinitializing renderer due to incorrect hidpi ratio");
+            screen_init_renderer_and_texture(screen);
+        }
 #endif
     }
 }
@@ -211,8 +214,29 @@ screen_init_rendering(struct screen *screen, const char *window_title,
 
     LOGI("Initial texture: %" PRIu16 "x%" PRIu16, frame_size.width,
                                                   frame_size.height);
-    return screen_init_renderer_and_texture(screen);
+    int ret = screen_init_renderer_and_texture(screen);
+#ifdef HIDPI_SUPPORT
+    int window_w, window_h, renderer_w, renderer_h;
+    SDL_GetWindowSize(screen->window, &window_w, &window_h);
+    SDL_GetRendererOutputSize(screen->renderer, &renderer_w, &renderer_h);
+    screen->expected_hidpi_w_factor = renderer_w * 1000 / window_w;
+    screen->expected_hidpi_h_factor = renderer_h * 1000 / window_h;
+#endif
+    return ret;
+}
+
+#ifdef HIDPI_SUPPORT
+bool
+screen_test_correct_hidpi_ratio(struct screen *screen) {
+  int window_w, window_h, renderer_w, renderer_h;
+  SDL_GetWindowSize(screen->window, &window_w, &window_h);
+  SDL_GetRendererOutputSize(screen->renderer, &renderer_w, &renderer_h);
+  int current_hidpi_w_factor = renderer_w * 1000 / window_w;
+  int current_hidpi_h_factor = renderer_h * 1000 / window_h;
+  return current_hidpi_w_factor == screen->expected_hidpi_w_factor &&
+         current_hidpi_h_factor == screen->expected_hidpi_h_factor;
 }
+#endif
 
 void
 screen_show_window(struct screen *screen) {
diff --git a/app/src/screen.h b/app/src/screen.h
index 6f002d13d7..4dd5366158 100644
--- a/app/src/screen.h
+++ b/app/src/screen.h
@@ -20,6 +20,10 @@ struct screen {
     bool has_frame;
     bool fullscreen;
     bool no_window;
+#ifdef HIDPI_SUPPORT
+    int expected_hidpi_w_factor; // multiplied by 1000 to avoid float
+    int expected_hidpi_h_factor; // multiplied by 1000 to avoid float
+#endif
 };
 
 #define SCREEN_INITIALIZER {  \
@@ -48,6 +52,15 @@ bool
 screen_init_rendering(struct screen *screen, const char *window_title,
                       struct size frame_size, bool always_on_top);
 
+#ifdef HIDPI_SUPPORT
+// test if the expected renderer to window ratio is correct
+// used to work around SDL bugs
+// returns true if correct.
+// If it returns false the renderer state needs to be fixed
+bool
+screen_test_correct_hidpi_ratio(struct screen *screen);
+#endif
+
 // reinitialize the renderer (only used in some configurations
 // if necessary to workaround SDL bugs)
 bool