[Bf-blender-cvs] [ac2a56d7f3d] master: Fix GHOST/Wayland display glitches on startup

[Campbell Barton]

Commit: ac2a56d7f3d6d20a0ed24ece11eea33e23d42f2c
Author: Campbell Barton
Date:   Sun Jun 12 17:44:12 2022 +1000
Branches: master
https://developer.blender.org/rBac2a56d7f3d6d20a0ed24ece11eea33e23d42f2c

Fix GHOST/Wayland display glitches on startup

Address two glitches on window creation:

- The DPI was zero until the `surface_enter` callback ran which happens
  after redrawing, causing the splash to display with incorrect scale
  before refreshing once the callback had run.

- The window scale was always 1, even when all outputs were HI-DPI.
  Now the maximum scale of all outputs is used. This isn't fool proof in
  the case of multiple monitors having different scales, however it
  doesn't seem possible to detect the scale used ahead of time
  (details in code-comment).

===================================================================

M	intern/ghost/intern/GHOST_WindowWayland.cpp

===================================================================

diff --git a/intern/ghost/intern/GHOST_WindowWayland.cpp b/intern/ghost/intern/GHOST_WindowWayland.cpp
index fdd1b47443b..051c826055d 100644
--- a/intern/ghost/intern/GHOST_WindowWayland.cpp
+++ b/intern/ghost/intern/GHOST_WindowWayland.cpp
@@ -30,8 +30,11 @@ struct window_t {
    */
   std::vector<const output_t *> outputs;
 
-  uint16_t dpi = 0;
-  int scale = 1;
+  /** The scale value written to #wl_surface_set_buffer_scale. */
+  int scale;
+  /** The DPI (currently always `scale * base_dpi`). */
+  uint16_t dpi;
+
   struct xdg_surface *xdg_surface;
   struct xdg_toplevel *xdg_toplevel;
   struct zxdg_toplevel_decoration_v1 *xdg_toplevel_decoration = nullptr;
@@ -46,6 +49,22 @@ struct window_t {
   int32_t size_pending[2];
 };
 
+/* -------------------------------------------------------------------- */
+/** \name Internal Utilities
+ * \{ */
+
+static int outputs_max_scale_or_default(const std::vector<output_t *> &outputs,
+                                        const int scale_default)
+{
+  int scale_max = 0;
+  for (const output_t *reg_output : outputs) {
+    scale_max = std::max(scale_max, reg_output->scale);
+  }
+  return scale_max ? scale_max : scale_default;
+}
+
+/** \} */
+
 /* -------------------------------------------------------------------- */
 /** \name Wayland Interface Callbacks
  *
@@ -214,8 +233,22 @@ GHOST_WindowWayland::GHOST_WindowWayland(GHOST_SystemWayland *system,
 
   w->is_dialog = is_dialog;
 
+  /* NOTE(@campbellbarton): The scale set here to avoid flickering on startup.
+   * When all monitors use the same scale (which is quite common) there aren't any problems.
+   *
+   * When monitors have different scales there may still be a visible window resize on startup.
+   * Ideally it would be possible to know the scale this window will use however that's only
+   * known once #surface_enter callback runs (which isn't guaranteed to run at all).
+   *
+   * Using the maximum scale is best as it results in the window first being smaller,
+   * avoiding a large window flashing before it's made smaller. */
+  w->scale = outputs_max_scale_or_default(this->m_system->outputs(), 1);
+  w->dpi = w->scale * base_dpi;
+
   /* Window surfaces. */
   w->surface = wl_compositor_create_surface(m_system->compositor());
+  wl_surface_set_buffer_scale(this->surface(), w->scale);
+
   wl_surface_add_listener(w->surface, &wl_surface_listener, this);
 
   w->egl_window = wl_egl_window_create(w->surface, int(w->size[0]), int(w->size[1]));
@@ -317,12 +350,7 @@ output_t *GHOST_WindowWayland::output_find_by_wl(struct wl_output *output)
 
 bool GHOST_WindowWayland::outputs_changed_update_scale()
 {
-  int scale_next = 0;
-  for (const output_t *reg_output : this->w->outputs) {
-    if (scale_next < reg_output->scale) {
-      scale_next = reg_output->scale;
-    }
-  }
+  const int scale_next = outputs_max_scale_or_default(this->m_system->outputs(), 0);
   if (scale_next == 0) {
     return false;
   }