From 8d9153fca25897bf40ca0ebac8b03616612cc7b4 Mon Sep 17 00:00:00 2001
From: humper <humper@google.com>
Date: Fri, 8 Aug 2014 12:06:13 -0700
Subject: [PATCH] short circuit high quality scales that are actually the
 identity transform

BUG=skia:
R=reed@google.com

Author: humper@google.com

Review URL: https://codereview.chromium.org/456843002
---
 src/core/SkBitmapProcState.cpp             | 22 ++++++++++++++++++++--
 src/core/SkBitmapProcState_matrixProcs.cpp |  3 +--
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/src/core/SkBitmapProcState.cpp b/src/core/SkBitmapProcState.cpp
index d48679e8c9..6a6cc75b6e 100644
--- a/src/core/SkBitmapProcState.cpp
+++ b/src/core/SkBitmapProcState.cpp
@@ -167,6 +167,22 @@ bool SkBitmapProcState::possiblyScaleImage() {
         SkScalar invScaleX = fInvMatrix.getScaleX();
         SkScalar invScaleY = fInvMatrix.getScaleY();
 
+        if (SkScalarNearlyEqual(invScaleX,1.0f) &&
+            SkScalarNearlyEqual(invScaleY,1.0f)) {
+            // short-circuit identity scaling; the output is supposed to
+            // be the same as the input, so we might as well go fast.
+
+            // Note(humper): We could also probably do this if the scales
+            // are close to -1 as well, since the flip doesn't require
+            // any fancy re-sampling...
+
+            // Set our filter level to low -- the only post-filtering this
+            // image might require is some interpolation if the translation
+            // is fractional.
+            fFilterLevel = SkPaint::kLow_FilterLevel;
+            return false;
+        }
+
         fScaledCacheID = SkScaledImageCache::FindAndLock(fOrigBitmap,
                                                          invScaleX, invScaleY,
                                                          &fScaledBitmap);
@@ -218,8 +234,10 @@ bool SkBitmapProcState::possiblyScaleImage() {
         fInvMatrix.setTranslate(fInvMatrix.getTranslateX() / fInvMatrix.getScaleX(),
                                 fInvMatrix.getTranslateY() / fInvMatrix.getScaleY());
 
-        // no need for any further filtering; we just did it!
-        fFilterLevel = SkPaint::kNone_FilterLevel;
+        // Set our filter level to low -- the only post-filtering this
+        // image might require is some interpolation if the translation
+        // is fractional.
+        fFilterLevel = SkPaint::kLow_FilterLevel;
         unlocker.release();
         return true;
     }
diff --git a/src/core/SkBitmapProcState_matrixProcs.cpp b/src/core/SkBitmapProcState_matrixProcs.cpp
index 02204b676b..851389c700 100644
--- a/src/core/SkBitmapProcState_matrixProcs.cpp
+++ b/src/core/SkBitmapProcState_matrixProcs.cpp
@@ -477,8 +477,7 @@ static void mirrorx_nofilter_trans(const SkBitmapProcState& s,
 SkBitmapProcState::MatrixProc SkBitmapProcState::chooseMatrixProc(bool trivial_matrix) {
 //    test_int_tileprocs();
     // check for our special case when there is no scale/affine/perspective
-    if (trivial_matrix) {
-        SkASSERT(SkPaint::kNone_FilterLevel == fFilterLevel);
+    if (trivial_matrix && SkPaint::kNone_FilterLevel == fFilterLevel) {
         fIntTileProcY = choose_int_tile_proc(fTileModeY);
         switch (fTileModeX) {
             case SkShader::kClamp_TileMode: