Only use the gainmap shader if we might need it

Skip using the gainmap shader when drawing to a bitmap
with a known SDR colorspace as it'll be a no-op in
rendering results since W=1.0, but it'll be very expensive
in runtime due to CPU evaluation of the SKSL shader.

Before:
createScaledBitmapWithGainmap_median (ns): 179,455,037

After:
createScaledBitmapWithGainmap_median (ns): 15,643,742

Bug: 311085927
Test: benchmark in CL
Change-Id: I3f2506a2bd86bbe29c6e0837d31e4a231a7c182a

4 files changed, 77 insertions, 2 deletions

diff --git a/apct-tests/perftests/core/res/drawable-nodpi/fountain_night.jpg b/apct-tests/perftests/core/res/drawable-nodpi/fountain_night.jpg
new file mode 100644
index 000000000000..d8b2d759e4c0
--- /dev/null
+++ b/apct-tests/perftests/core/res/drawable-nodpi/fountain_night.jpg
diff --git a/apct-tests/perftests/core/src/android/graphics/perftests/CanvasPerfTest.java b/apct-tests/perftests/core/src/android/graphics/perftests/CanvasPerfTest.java
index f84a0d037ca5..e5a06c9bd146 100644
--- a/apct-tests/perftests/core/src/android/graphics/perftests/CanvasPerfTest.java
+++ b/apct-tests/perftests/core/src/android/graphics/perftests/CanvasPerfTest.java
@@ -16,20 +16,29 @@
 
 package android.graphics.perftests;
 
+import static org.junit.Assert.assertTrue;
+
+import android.content.Context;
 import android.graphics.Bitmap;
 import android.graphics.Bitmap.Config;
 import android.graphics.Color;
+import android.graphics.ImageDecoder;
 import android.graphics.Paint;
 import android.graphics.RecordingCanvas;
 import android.graphics.RenderNode;
 import android.perftests.utils.BenchmarkState;
 import android.perftests.utils.PerfStatusReporter;
 
+import androidx.test.InstrumentationRegistry;
 import androidx.test.filters.LargeTest;
 
+import com.android.perftests.core.R;
+
 import org.junit.Rule;
 import org.junit.Test;
 
+import java.io.IOException;
+
 @LargeTest
 public class CanvasPerfTest {
     @Rule
@@ -93,4 +102,38 @@ public class CanvasPerfTest {
             node.end(canvas);
         }
     }
+
+    @Test
+    public void testCreateScaledBitmap() throws IOException {
+        BenchmarkState state = mPerfStatusReporter.getBenchmarkState();
+        final Context context = InstrumentationRegistry.getContext();
+        Bitmap source = ImageDecoder.decodeBitmap(
+                ImageDecoder.createSource(context.getResources(), R.drawable.fountain_night),
+                (decoder, info, source1) -> {
+                    decoder.setAllocator(ImageDecoder.ALLOCATOR_SOFTWARE);
+                });
+        source.setGainmap(null);
+
+        while (state.keepRunning()) {
+            Bitmap.createScaledBitmap(source, source.getWidth() / 2, source.getHeight() / 2, true)
+                    .recycle();
+        }
+    }
+
+    @Test
+    public void testCreateScaledBitmapWithGainmap() throws IOException {
+        BenchmarkState state = mPerfStatusReporter.getBenchmarkState();
+        final Context context = InstrumentationRegistry.getContext();
+        Bitmap source = ImageDecoder.decodeBitmap(
+                ImageDecoder.createSource(context.getResources(), R.drawable.fountain_night),
+                (decoder, info, source1) -> {
+                    decoder.setAllocator(ImageDecoder.ALLOCATOR_SOFTWARE);
+                });
+        assertTrue(source.hasGainmap());
+
+        while (state.keepRunning()) {
+            Bitmap.createScaledBitmap(source, source.getWidth() / 2, source.getHeight() / 2, true)
+                    .recycle();
+        }
+    }
 }
diff --git a/libs/hwui/SkiaCanvas.cpp b/libs/hwui/SkiaCanvas.cpp
index 31fc929dfcdf..008ea3aaa2e7 100644
--- a/libs/hwui/SkiaCanvas.cpp
+++ b/libs/hwui/SkiaCanvas.cpp
@@ -589,10 +589,40 @@ void SkiaCanvas::drawMesh(const Mesh& mesh, sk_sp<SkBlender> blender, const Pain
 // Canvas draw operations: Bitmaps
 // ----------------------------------------------------------------------------
 
+bool SkiaCanvas::useGainmapShader(Bitmap& bitmap) {
+    // If the bitmap doesn't have a gainmap, don't use the gainmap shader
+    if (!bitmap.hasGainmap()) return false;
+
+    // If we don't have an owned canvas, then we're either hardware accelerated or drawing
+    // to a picture - use the gainmap shader out of caution. Ideally a picture canvas would
+    // use a drawable here instead to defer making that decision until the last possible
+    // moment
+    if (!mCanvasOwned) return true;
+
+    auto info = mCanvasOwned->imageInfo();
+
+    // If it's an unknown colortype then it's not a bitmap-backed canvas
+    if (info.colorType() == SkColorType::kUnknown_SkColorType) return true;
+
+    skcms_TransferFunction tfn;
+    info.colorSpace()->transferFn(&tfn);
+
+    auto transferType = skcms_TransferFunction_getType(&tfn);
+    switch (transferType) {
+        case skcms_TFType_HLGish:
+        case skcms_TFType_HLGinvish:
+        case skcms_TFType_PQish:
+            return true;
+        case skcms_TFType_Invalid:
+        case skcms_TFType_sRGBish:
+            return false;
+    }
+}
+
 void SkiaCanvas::drawBitmap(Bitmap& bitmap, float left, float top, const Paint* paint) {
     auto image = bitmap.makeImage();
 
-    if (bitmap.hasGainmap()) {
+    if (useGainmapShader(bitmap)) {
         Paint gainmapPaint = paint ? *paint : Paint();
         sk_sp<SkShader> gainmapShader = uirenderer::MakeGainmapShader(
                 image, bitmap.gainmap()->bitmap->makeImage(), bitmap.gainmap()->info,
@@ -619,7 +649,7 @@ void SkiaCanvas::drawBitmap(Bitmap& bitmap, float srcLeft, float srcTop, float s
     SkRect srcRect = SkRect::MakeLTRB(srcLeft, srcTop, srcRight, srcBottom);
     SkRect dstRect = SkRect::MakeLTRB(dstLeft, dstTop, dstRight, dstBottom);
 
-    if (bitmap.hasGainmap()) {
+    if (useGainmapShader(bitmap)) {
         Paint gainmapPaint = paint ? *paint : Paint();
         sk_sp<SkShader> gainmapShader = uirenderer::MakeGainmapShader(
                 image, bitmap.gainmap()->bitmap->makeImage(), bitmap.gainmap()->info,
diff --git a/libs/hwui/SkiaCanvas.h b/libs/hwui/SkiaCanvas.h
index ced02241ffe2..4bf1790e2415 100644
--- a/libs/hwui/SkiaCanvas.h
+++ b/libs/hwui/SkiaCanvas.h
@@ -223,6 +223,8 @@ private:
 
     void drawPoints(const float* points, int count, const Paint& paint, SkCanvas::PointMode mode);
 
+    bool useGainmapShader(Bitmap& bitmap);
+
     class Clip;
 
     std::unique_ptr<SkCanvas> mCanvasOwned;  // Might own a canvas we allocated.