gsk: Don't use gpu renderers with llvmpipe

Unless the renderer has been explicitly selected via the
GSK_RENDERER environment variable, don't use it with llvmpipe.

It is important that we allow explicit setting to override
this, so we can continue to use ngl in ci, where we don't
have hw and want to test with llvmpipe.

This should address many of the "performance is terrible in
GNOME OS" complaints that are coming from people running in
VMs, etc.

gsk/gskrenderer.c

@@ -46,6 +46,8 @@
 
 #include "gl/gskglrenderer.h"
 #include "gpu/gskvulkanrenderer.h"
+#include "gdk/gdkvulkancontextprivate.h"
+#include "gdk/gdkdisplayprivate.h"
 
 #include <graphene-gobject.h>
 #include <cairo-gobject.h>
@@ -630,16 +632,56 @@ get_renderer_for_backend (GdkSurface *surface)
   return G_TYPE_INVALID;
 }
 
+static gboolean
+gl_software_rendering (GdkSurface *surface)
+{
+  GdkDisplay *display = gdk_surface_get_display (surface);
+  GdkGLContext *context;
+
+  if (!gdk_display_prepare_gl (display, NULL))
+    return G_TYPE_INVALID;
+
+  context = gdk_display_get_gl_context (display);
+  gdk_gl_context_make_current (context);
+
+  return strstr ((const char *) glGetString (GL_RENDERER), "llvmpipe") != NULL;
+}
+
 static GType
 get_renderer_for_gl (GdkSurface *surface)
 {
+  if (gl_software_rendering (surface))
+    return G_TYPE_INVALID;
+
   return gsk_ngl_renderer_get_type ();
 }
 
+#ifdef GDK_RENDERING_VULKAN
+static gboolean
+vulkan_software_rendering (GdkSurface *surface)
+{
+  GdkDisplay *display = gdk_surface_get_display (surface);
+  GdkVulkanContext *context = gdk_display_create_vulkan_context (display, surface, NULL);
+  VkPhysicalDevice device;
+  VkPhysicalDeviceProperties props;
+
+  if (!context)
+    return G_TYPE_INVALID;
+
+  device = gdk_vulkan_context_get_physical_device (context);
+  vkGetPhysicalDeviceProperties (device, &props);
+
+  return props.deviceType == VK_PHYSICAL_DEVICE_TYPE_CPU;
+}
+#endif
+
 static GType
 get_renderer_for_vulkan (GdkSurface *surface)
 {
 #ifdef GDK_RENDERING_VULKAN
+  if (vulkan_software_rendering (surface))
+    return G_TYPE_INVALID;
+
   return GSK_TYPE_VULKAN_RENDERER;
 #else
   return G_TYPE_INVALID;
@@ -649,6 +691,9 @@ get_renderer_for_vulkan (GdkSurface *surface)
 static GType
 get_renderer_for_gles2 (GdkSurface *surface)
 {
+  if (gl_software_rendering (surface))
+    return G_TYPE_INVALID;
+
   return GSK_TYPE_GL_RENDERER;
 }