vulkan: Create multiple render objects

Sometimes the GPU is still busy when the next frame starts (like when
no-vsync benchmarking), so we need to keep all those resources alone and
create new ones.
That's what the render object is for, so we just create another one.

However, when we create too many, we'll starve the CPU. So we'll limit
it. Currently, that limit is at 4, but I've never reached it (I've also
not starved the GPU yet), so that number may want to be set lower/higher
in the future.

Note that this is different from the number of outstanding buffers, as
those are not busy on the GPU but on the compositor, and as such a
buffer may have not finished rendering but have been returend from the
compositor (very busy GPU) or have finished rendering but not been
returned from the compositor (very idle GPU).

gsk/vulkan/gskvulkanrender.c

@@ -350,6 +350,12 @@ gsk_vulkan_render_get_framebuffer (GskVulkanRender *self,
   return fb->framebuffer;
 }
 
+VkFence
+gsk_vulkan_render_get_fence (GskVulkanRender *self)
+{
+  return self->fence;
+}
+
 void
 gsk_vulkan_render_add_cleanup_image (GskVulkanRender *self,
                                      GskVulkanImage  *image)

gsk/vulkan/gskvulkanrenderer.c

@@ -17,6 +17,8 @@
 
 #include <graphene.h>
 
+#define GSK_VULKAN_MAX_RENDERS 4
+
 typedef struct _GskVulkanTextureData GskVulkanTextureData;
 
 struct _GskVulkanTextureData {
@@ -51,7 +53,7 @@ struct _GskVulkanRenderer
   guint n_targets;
   GskVulkanImage **targets;
 
-  GskVulkanRender *render;
+  GskVulkanRender *renders[GSK_VULKAN_MAX_RENDERS];
 
   GSList *textures;
 
@@ -161,6 +163,38 @@ gsk_vulkan_renderer_update_images_cb (GdkVulkanContext  *context,
     }
 }
 
+static GskVulkanRender *
+gsk_vulkan_renderer_get_render (GskVulkanRenderer *self)
+{
+  VkFence fences[G_N_ELEMENTS (self->renders)];
+  VkDevice device;
+  guint i;
+
+  device = gdk_vulkan_context_get_device (self->vulkan);
+
+  while (TRUE)
+    {
+      for (i = 0; i < G_N_ELEMENTS (self->renders); i++)
+        {
+          if (self->renders[i] == NULL)
+            {
+              self->renders[i] = gsk_vulkan_render_new (GSK_RENDERER (self), self->vulkan);
+              return self->renders[i];
+            }
+
+          fences[i] = gsk_vulkan_render_get_fence (self->renders[i]);
+          if (vkGetFenceStatus (device, fences[i]) == VK_SUCCESS)
+            return self->renders[i];
+        }
+
+      GSK_VK_CHECK (vkWaitForFences, device,
+                                     G_N_ELEMENTS (fences),
+                                     fences,
+                                     VK_FALSE,
+                                     INT64_MAX);
+    }
+}
+
 static gboolean
 gsk_vulkan_renderer_realize (GskRenderer  *renderer,
                              GdkSurface   *surface,
@@ -185,8 +219,6 @@ gsk_vulkan_renderer_realize (GskRenderer  *renderer,
                     self);
   gsk_vulkan_renderer_update_images_cb (self->vulkan, self);
 
-  self->render = gsk_vulkan_render_new (renderer, self->vulkan);
-
   self->glyph_cache = gsk_vulkan_glyph_cache_new (renderer, self->vulkan);
 
   return TRUE;
@@ -197,6 +229,7 @@ gsk_vulkan_renderer_unrealize (GskRenderer *renderer)
 {
   GskVulkanRenderer *self = GSK_VULKAN_RENDERER (renderer);
   GSList *l;
+  guint i;
 
   g_clear_object (&self->glyph_cache);
 
@@ -209,7 +242,8 @@ gsk_vulkan_renderer_unrealize (GskRenderer *renderer)
     }
   g_clear_pointer (&self->textures, g_slist_free);
 
-  g_clear_pointer (&self->render, gsk_vulkan_render_free);
+  for (i = 0; i < G_N_ELEMENTS (self->renders); i++)
+    g_clear_pointer (&self->renders[i], gsk_vulkan_render_free);
 
   gsk_vulkan_renderer_free_targets (self);
   g_signal_handlers_disconnect_by_func(self->vulkan,
@@ -306,7 +340,7 @@ gsk_vulkan_renderer_render (GskRenderer          *renderer,
 #endif
 
   gdk_draw_context_begin_frame (GDK_DRAW_CONTEXT (self->vulkan), region);
-  render = self->render;
+  render = gsk_vulkan_renderer_get_render (self);
 
   render_region = get_render_region (self);
   draw_index = gdk_vulkan_context_get_draw_index (self->vulkan);

gsk/vulkan/gskvulkanrenderprivate.h

@@ -95,6 +95,7 @@ void                    gsk_vulkan_render_submit                        (GskVulk
 GdkTexture *            gsk_vulkan_render_download_target               (GskVulkanRender        *self);
 VkFramebuffer           gsk_vulkan_render_get_framebuffer               (GskVulkanRender        *self,
                                                                          GskVulkanImage         *image);
+VkFence                 gsk_vulkan_render_get_fence                     (GskVulkanRender        *self);
 
 G_END_DECLS