[client] overlay: rework the interface to avoid possible race conditions

client/include/app.h

@@ -81,7 +81,16 @@ void app_glSwapBuffers(void);
 #endif
 
 void app_registerOverlay(const struct LG_OverlayOps * ops, void * params);
+
+/**
+ * render the overlay
+ * returns:
+ *   -1 for no overlay
+ *    0 for full output damage
+ *   >0 number of rects written into rects
+ */
 int app_renderOverlay(struct Rect * rects, int maxRects);
+
 void app_freeOverlays(void);
 
 struct OverlayGraph;

client/include/interface/overlay.h

@@ -46,23 +46,21 @@ struct LG_OverlayOps
   /* general state flags, may be changed at any time */
   enum LG_OverlayFlags flags;
 
-  /* get the number of windows that will be rendered when `render` is called
-   *
-   *`interactive` is true if the application is currently in overlay interaction
-   * mode
-   */
-  int (*getWindowCount)(void * udata, bool interactive);
-
   /* perform the actual drawing/rendering
    *
    * `interactive` is true if the application is currently in overlay interaction
    * mode.
    *
-   * The caller provides `windowRects` to be populated by the callee and is sized
-   * according to the return value of `getWindowCount`. Note, `windowRects` may
-   * be NULL if the caller does not want this information.
+   * `windowRects` is an array of window rects that were rendered using screen
+   * coordinates. Will be `NULL` if the information is not required.
+   *
+   * `maxRects` is the length of `windowRects`, or 0 if `windowRects` is `NULL`
+   *
+   * returns the number of rects written to `windowRects`, or -1 if there is not
+   * enough room left.
    */
-  void (*render)(void * udata, bool interactive, struct Rect windowRects[]);
+  int (*render)(void * udata, bool interactive, struct Rect * windowRects,
+      int maxRects);
 
   /* TODO: add load/save settings capabillity */
 };
@@ -71,7 +69,6 @@ struct LG_OverlayOps
   assert((x)->name          ); \
   assert((x)->init          ); \
   assert((x)->free          ); \
-  assert((x)->getWindowCount); \
   assert((x)->render        );
 
 #endif

client/src/app.c

@@ -628,7 +628,6 @@ struct Overlay
 {
   const struct LG_OverlayOps * ops;
   void * udata;
-  int windowCount;
 };
 
 void app_registerOverlay(const struct LG_OverlayOps * ops, void * params)
@@ -650,43 +649,40 @@ void app_registerOverlay(const struct LG_OverlayOps * ops, void * params)
 
 int app_renderOverlay(struct Rect * rects, int maxRects)
 {
-  int windowCount = 0;
+  int  totalRects  = 0;
+  bool totalDamage = false;
   struct Overlay * overlay;
 
-  // get the total window count
-  for (ll_reset(g_state.overlays);
-      ll_walk(g_state.overlays, (void **)&overlay); )
-  {
-    overlay->windowCount = overlay->ops->getWindowCount(overlay->udata, false);
-    windowCount += overlay->windowCount;
-  }
-
-  // return -1 if there are no windows to render
-  if (windowCount == 0)
-    return -1;
-
-  if (windowCount > maxRects)
-  {
-    rects = NULL;
-    windowCount = 0;
-  }
+  igNewFrame();
 
   // render the overlays
-  igNewFrame();
   for (ll_reset(g_state.overlays);
       ll_walk(g_state.overlays, (void **)&overlay); )
   {
-    if (overlay->windowCount == 0)
+    const int written =
+      overlay->ops->render(overlay->udata, false, rects, maxRects);
+
+    if (!totalDamage)
       continue;
 
-    overlay->ops->render(overlay->udata, false, rects);
-    if (rects)
-      rects += overlay->windowCount;
+    if (written == -1)
+    {
+      // out of rects, return that the entire surface is damaged
+      totalDamage = true;
+      rects       = NULL;
+      maxRects    = 0;
+      totalRects  = 0;
+    }
+    else
+    {
+      maxRects -= written;
+      rects    += written;
+    }
   }
 
   igRender();
 
-  return windowCount;
+  return totalDamage ? -1 : totalRects;
 }
 
 void app_freeOverlays(void)

client/src/overlay/fps.c

@@ -32,14 +32,13 @@ static void fps_free(void * udata)
 {
 }
 
-static int fps_getWindowCount(void * udata, bool interactive)
+static int fps_render(void * udata, bool interactive, struct Rect * windowRects,
+    int maxRects)
 {
-  return g_state.showFPS ? 1 : 0;
-}
+  if (!g_state.showFPS)
+    return 0;
 
-static void fps_render(void * udata, bool interactive, struct Rect * windowRects)
-{
-  const ImVec2 pos = {0.0f, 0.0f};
+  ImVec2 pos = {0.0f, 0.0f};
   igSetNextWindowBgAlpha(0.6f);
   igSetNextWindowPos(pos, 0, pos);
 
@@ -55,18 +54,21 @@ static void fps_render(void * udata, bool interactive, struct Rect * windowRects
       atomic_load_explicit(&g_state.fps, memory_order_relaxed),
       atomic_load_explicit(&g_state.ups, memory_order_relaxed));
 
-  if (windowRects)
+  if (maxRects == 0)
   {
-    ImVec2 pos, size;
+    return -1;
+    igEnd();
+  }
+
+  ImVec2 size;
   igGetWindowPos(&pos);
   igGetWindowSize(&size);
   windowRects[0].x = pos.x;
   windowRects[0].y = pos.y;
   windowRects[0].w = size.x;
   windowRects[0].h = size.y;
-  }
-
   igEnd();
+  return 1;
 }
 
 struct LG_OverlayOps LGOverlayFPS =
@@ -74,6 +76,5 @@ struct LG_OverlayOps LGOverlayFPS =
   .name           = "FPS",
   .init           = fps_init,
   .free           = fps_free,
-  .getWindowCount = fps_getWindowCount,
   .render         = fps_render
 };

client/src/overlay/graphs.c

@@ -54,11 +54,6 @@ static void graphs_free(void * udata)
   ll_free(gs.graphs);
 }
 
-static int graphs_getWindowCount(void * udata, bool interactive)
-{
-  return g_state.showTiming ? 1 : 0;
-}
-
 struct BufferMetrics
 {
   float min;
@@ -91,9 +86,13 @@ static bool rbCalcMetrics(int index, void * value_, void * udata_)
   return true;
 }
 
-static void graphs_render(void * udata, bool interactive, struct Rect * windowRects)
+static int graphs_render(void * udata, bool interactive,
+    struct Rect * windowRects, int maxRects)
 {
-  const ImVec2 pos = {0.0f, 0.0f};
+  if (!g_state.showTiming)
+    return 0;
+
+  ImVec2 pos = {0.0f, 0.0f};
   igSetNextWindowBgAlpha(0.4f);
   igSetNextWindowPos(pos, 0, pos);
 
@@ -139,18 +138,22 @@ static void graphs_render(void * udata, bool interactive, struct Rect * windowRe
         sizeof(float));
   };
 
-  if (windowRects)
+  if (maxRects == 0)
   {
-    ImVec2 pos, size;
+    igEnd();
+    return -1;
+  }
+
+  ImVec2 size;
   igGetWindowPos(&pos);
   igGetWindowSize(&size);
   windowRects[0].x = pos.x;
   windowRects[0].y = pos.y;
   windowRects[0].w = size.x;
   windowRects[0].h = size.y;
-  }
 
   igEnd();
+  return 1;
 }
 
 struct LG_OverlayOps LGOverlayGraphs =
@@ -158,7 +161,6 @@ struct LG_OverlayOps LGOverlayGraphs =
   .name           = "Graphs",
   .init           = graphs_init,
   .free           = graphs_free,
-  .getWindowCount = graphs_getWindowCount,
   .render         = graphs_render
 };