Less aggressive glyphs precaching

The renderer used to pre-cache glyphs at record time. This then changed
to pre-caching at the beginning of every frame. This unfortunately entails
a lot of duplicate work on every frame, which amounts to 0.5 to 1ms in
some stock applications.

This change is somewhere in the middle: pre-caching happens the first
time a DrawTextOp is deferred or every time the screen-space transform
is different from the last pre-caching operation.

Change-Id: Id6d9e2599d90a5b75010b0f0a28746befbf3c205
diff --git a/libs/hwui/font/Font.cpp b/libs/hwui/font/Font.cpp
index c932087..02c1aa1 100644
--- a/libs/hwui/font/Font.cpp
+++ b/libs/hwui/font/Font.cpp
@@ -15,10 +15,12 @@
  */
 
 #define LOG_TAG "OpenGLRenderer"
+#define ATRACE_TAG ATRACE_TAG_VIEW
 
 #include <cutils/compiler.h>
 
 #include <utils/JenkinsHash.h>
+#include <utils/Trace.h>
 
 #include <SkGlyph.h>
 #include <SkUtils.h>
@@ -261,11 +263,8 @@
 }
 
 CachedGlyphInfo* Font::getCachedGlyph(SkPaint* paint, glyph_t textUnit, bool precaching) {
-    CachedGlyphInfo* cachedGlyph = NULL;
-    ssize_t index = mCachedGlyphs.indexOfKey(textUnit);
-    if (index >= 0) {
-        cachedGlyph = mCachedGlyphs.valueAt(index);
-
+    CachedGlyphInfo* cachedGlyph = mCachedGlyphs.valueFor(textUnit);
+    if (cachedGlyph) {
         // Is the glyph still in texture cache?
         if (!cachedGlyph->mIsValid) {
             const SkGlyph& skiaGlyph = GET_METRICS(paint, textUnit,
@@ -346,11 +345,13 @@
 }
 
 void Font::precache(SkPaint* paint, const char* text, int numGlyphs) {
+    ATRACE_NAME("precacheText");
+
     if (numGlyphs == 0 || text == NULL) {
         return;
     }
-    int glyphsCount = 0;
 
+    int glyphsCount = 0;
     while (glyphsCount < numGlyphs) {
         glyph_t glyph = GET_GLYPH(text);
 
@@ -360,7 +361,6 @@
         }
 
         CachedGlyphInfo* cachedGlyph = getCachedGlyph(paint, glyph, true);
-
         glyphsCount++;
     }
 }