respect srgb gamma when building mips

gm/mipmap.cpp

Index: gm/mipmap.cpp
diff --git a/gm/mipmap.cpp b/gm/mipmap.cpp
index ae73a8de9db19259bd4114cfa50b54acd552333f..1ce8d0b263cd0ec7e85def54fa52602c531dafca 100644
--- a/gm/mipmap.cpp
+++ b/gm/mipmap.cpp
@@ -11,8 +11,8 @@
 #include "SkRandom.h"
 #include "SkSurface.h"
 
-static sk_sp<SkImage> make_image() {
-    const SkImageInfo info = SkImageInfo::MakeN32Premul(319, 52);
+static sk_sp<SkImage> make_image(bool useSRGB) {
+    const SkImageInfo info = SkImageInfo::MakeS32(319, 52, kPremul_SkAlphaType);
     auto surface(SkSurface::MakeRaster(info));
     SkCanvas* canvas = surface->getCanvas();
     canvas->drawColor(sk_tool_utils::color_to_565(0xFFF8F8F8));
@@ -21,29 +21,42 @@ static sk_sp<SkImage> make_image() {
     paint.setAntiAlias(true);
 
     paint.setStyle(SkPaint::kStroke_Style);
+    paint.setStrokeWidth(2);
     for (int i = 0; i < 20; ++i) {
         canvas->drawCircle(-4, 25, 20, paint);
         canvas->translate(25, 0);
     }
-    return surface->makeImageSnapshot();
+    auto img = surface->makeImageSnapshot();
+    if (useSRGB) {
+        return img;
+    } else {
+        SkBitmap bm;
+        bm.allocN32Pixels(info.width(), info.height());
+        img->readPixels(bm.info(), bm.getPixels(), bm.rowBytes(), 0, 0);
+        bm.setImmutable();
+        return SkImage::MakeFromBitmap(bm);
+    }
 }
 
-DEF_SIMPLE_GM(mipmap, canvas, 400, 200) {
-    sk_sp<SkImage> img(make_image());//SkImage::NewFromEncoded(data));
-
+DEF_SIMPLE_GM(mipmap, canvas, 420, 200) {
     SkPaint paint;
     const SkRect dst = SkRect::MakeWH(177, 15);
+    const SkRect clip = SkRect::MakeWH(200, 200);
 
     paint.setTextSize(30);
-    SkString str;
-    str.printf("scale %g %g", dst.width() / img->width(), dst.height() / img->height());
-//    canvas->drawText(str.c_str(), str.size(), 300, 100, paint);
 
-    canvas->translate(20, 20);
-    for (int i = 0; i < 4; ++i) {
-        paint.setFilterQuality(SkFilterQuality(i));
-        canvas->drawImageRect(img.get(), dst, &paint);
-        canvas->translate(0, 20);
+    for (bool useSRGB : { false, true }) {
+        sk_sp<SkImage> img(make_image(useSRGB));
+        canvas->save();
+        canvas->clipRect(clip);
+        canvas->translate(20, 20);
+        for (int i = 0; i < 4; ++i) {
+            paint.setFilterQuality(SkFilterQuality(i));
+            canvas->drawImageRect(img.get(), dst, &paint);
+            canvas->translate(0, 20);
+        }
+        canvas->drawImage(img.get(), 0, 20, nullptr);
+        canvas->restore();
+        canvas->translate(200, 0);
     }
-    canvas->drawImage(img.get(), 20, 20, nullptr);
 }