Use kLow_SkFilterQuality in generateGlyphImage

This reduces jank when flinging a page of emoji on Android (I have separately shared out a spreadsheet). Arguably, the quality loss should be acceptable since we shouldn't be down-scaling that much (magnitude-wise not frequency-wise). Ideally, we would add a raster mode where we would draw at the correct size w/o generating the mip maps.

Change-Id: Id91d638db1b2457567e54c264ed3fa5d10316976
Reviewed-on: https://skia-review.googlesource.com/33763
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/src/ports/SkFontHost_FreeType_common.cpp b/src/ports/SkFontHost_FreeType_common.cpp
index a216fdb29c..864f75dee8 100644
--- a/src/ports/SkFontHost_FreeType_common.cpp
+++ b/src/ports/SkFontHost_FreeType_common.cpp
@@ -585,7 +585,15 @@ void SkScalerContext_FreeType_Base::generateGlyphImage(
             canvas.translate(face->glyph->bitmap_left, -face->glyph->bitmap_top);
 
             SkPaint paint;
-            paint.setFilterQuality(kMedium_SkFilterQuality);
+            // Using kMedium FilterQuality will cause mipmaps to be generated. Use
+            // kLow when the results will be roughly the same in order to avoid
+            // the mipmap generation cost.
+            // See skbug.com/6967
+            if (bitmapTransform.getMinScale() < 0.5) {
+                paint.setFilterQuality(kMedium_SkFilterQuality);
+            } else {
+                paint.setFilterQuality(kLow_SkFilterQuality);
+            }
             canvas.drawBitmap(unscaledBitmap, 0, 0, &paint);
 
             // If the destination is BW or LCD, convert from A8.