[gpu] Re-upload textures when a the internal Surface bitmap changes

We can use the internal SkBitmap generation ID in the SkiaSurface to
know if the uploaded texture is already outdated and we have to
re-upload it to the GPU.

os/skia/skia_surface.cpp

@@ -797,6 +797,10 @@ const SkImage* SkiaSurface::getOrCreateTextureImage() const
   if (!win || !win->sk_grCtx())
     return nullptr;
 
+  // Invalidate the cached texture if the bitmap pixels were modified.
+  if (m_cachedGen && m_cachedGen != m_bitmap.getGenerationID())
+    m_image.reset();
+
   if (m_image && m_image->isValid(win->sk_grCtx()))
     return m_image.get();
   if (uploadBitmapAsTexture() &&
@@ -828,6 +832,9 @@ bool SkiaSurface::uploadBitmapAsTexture() const
     ii.alphaType(),
     nullptr);
 
+  if (m_image)
+    m_cachedGen = m_bitmap.getGenerationID();
+
   return (m_image != nullptr);
 }
 

os/skia/skia_surface.h

@@ -148,6 +148,8 @@ class SkiaSurface final : public Surface {
 
   SkBitmap m_bitmap;
 #if SK_SUPPORT_GPU
+  // Cached m_bitmap generation in the GPU texture.
+  mutable uint32_t m_cachedGen = 0;
   mutable sk_sp<SkImage> m_image;
 #endif
   sk_sp<SkSurface> m_surface;