Reland "Clear out atlases if they haven't been used in a while."

This is a reland of 79007c9

Original change's description:
> Clear out atlases if they haven't been used in a while.
> 
> This will stage out atlas pages one at a time with an interval of
> 256 flushes between them. Also removes the last page to help
> conserve memory if text or other atlas-using systems are not in use.
> 
> Bug: 1058905
> Change-Id: I8717621033068d0e24da944356d91b0f35e5373b
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/276764
> Commit-Queue: Jim Van Verth <[email protected]>
> Reviewed-by: Herb Derby <[email protected]>

Bug: 1058905
Change-Id: I25b0037cb1608ae0bda641e0d0588afaf3dd47e5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/276960
Reviewed-by: Jim Van Verth <[email protected]>
Commit-Queue: Jim Van Verth <[email protected]>

Author: jvanverth

src/gpu/GrDrawOpAtlas.cpp

@@ -221,6 +221,7 @@ GrDrawOpAtlas::GrDrawOpAtlas(
         , fGenerationCounter(generationCounter)
         , fAtlasGeneration(fGenerationCounter->next())
         , fPrevFlushToken(GrDeferredUploadToken::AlreadyFlushedToken())
+        , fFlushesSinceLastUse(0)
         , fMaxPages(AllowMultitexturing::kYes == allowMultitexturing ? kMaxMultitexturePages : 1)
         , fNumActivePages(0) {
     int numPlotsX = width/plotWidth;
@@ -407,11 +408,13 @@ GrDrawOpAtlas::ErrorCode GrDrawOpAtlas::addToAtlas(GrResourceProvider* resourceP
 }
 
 void GrDrawOpAtlas::compact(GrDeferredUploadToken startTokenForNextFlush) {
-    if (fNumActivePages <= 1) {
+    if (fNumActivePages < 1) {
         fPrevFlushToken = startTokenForNextFlush;
         return;
     }
 
+    ++fFlushesSinceLastUse;
+
     // For all plots, reset number of flushes since used if used this frame.
     PlotList::Iter plotIter;
     bool atlasUsedThisFlush = false;
@@ -428,11 +431,11 @@ void GrDrawOpAtlas::compact(GrDeferredUploadToken startTokenForNextFlush) {
         }
     }
 
-    // We only try to compact if the atlas was used in the recently completed flush.
+    // We only try to compact if the atlas was used in the recently completed flush or
+    // hasn't been used in a long time.
     // This is to handle the case where a lot of text or path rendering has occurred but then just
     // a blinking cursor is drawn.
-    // TODO: consider if we should also do this if it's been a long time since the last atlas use
-    if (atlasUsedThisFlush) {
+    if (atlasUsedThisFlush || fFlushesSinceLastUse > kRecentlyUsedCount) {
         SkTArray<Plot*> availablePlots;
         uint32_t lastPageIndex = fNumActivePages - 1;
 
@@ -537,14 +540,16 @@ void GrDrawOpAtlas::compact(GrDeferredUploadToken startTokenForNextFlush) {
         }
 
         // If none of the plots in the last page have been used recently, delete it.
-        if (!usedPlots) {
+        if (!usedPlots || fFlushesSinceLastUse > kRecentlyUsedCount) {
 #ifdef DUMP_ATLAS_DATA
             if (gDumpAtlasData) {
-                SkDebugf("delete %d\n", fNumPages-1);
+                SkDebugf("delete %d\n", fNumActivePages-1);
             }
 #endif
             this->deactivateLastPage();
         }
+
+        fFlushesSinceLastUse = 0;
     }
 
     fPrevFlushToken = startTokenForNextFlush;

src/gpu/GrDrawOpAtlas.h

@@ -435,6 +435,9 @@ class GrDrawOpAtlas {
     // nextTokenToFlush() value at the end of the previous flush
     GrDeferredUploadToken fPrevFlushToken;
 
+    // the number of flushes since this atlas has been last used
+    int                   fFlushesSinceLastUse;
+
     std::vector<EvictionCallback*> fEvictionCallbacks;
 
     struct Page {