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..45b4d1512636cc5fbdb6e1e57cb5f930e517be53 100644
--- a/gm/mipmap.cpp
+++ b/gm/mipmap.cpp
@@ -47,3 +47,52 @@ DEF_SIMPLE_GM(mipmap, canvas, 400, 200) {
     }
     canvas->drawImage(img.get(), 20, 20, nullptr);
 }
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+// create a circle image computed raw, so we can wrap it as a linear or srgb image
+static sk_sp<SkImage> make(sk_sp<SkColorSpace> cs) {
+    const int N = 100;
+    SkImageInfo info = SkImageInfo::Make(N, N, kN32_SkColorType, kPremul_SkAlphaType, cs);
+    SkBitmap bm;
+    bm.allocPixels(info);
+
+    for (int y = 0; y < N; ++y) {
+        for (int x = 0; x < N; ++x) {
+            *bm.getAddr32(x, y) = (x ^ y) & 1 ? 0xFFFFFFFF : 0xFF000000;
+        }
+    }
+    bm.setImmutable();
+    return SkImage::MakeFromBitmap(bm);
+}
+
+static void show_mips(SkCanvas* canvas, SkImage* img) {
+    SkPaint paint;
+    paint.setFilterQuality(kMedium_SkFilterQuality);
+
+    SkRect dst = SkRect::MakeIWH(img->width(), img->height());
+    while (dst.width() > 5) {
+        canvas->drawImageRect(img, dst, &paint);
+        dst.offset(dst.width() + 10, 0);
+        dst.fRight = dst.fLeft + SkScalarHalf(dst.width());
+        dst.fBottom = dst.fTop + SkScalarHalf(dst.height());
+    }
+}
+
+/*
+ *  Ensure that in L32 drawing mode, both images/mips look the same as each other, and
+ *  their mips are darker than the original (since the mips should ignore the gamma in L32).
+ *
+ *  Ensure that in S32 drawing mode, all images/mips look the same, and look correct (i.e.
+ *  the mip levels match the original in brightness).
+ */
+DEF_SIMPLE_GM(mipmap_srgb, canvas, 260, 230) {
+    sk_sp<SkImage> limg = make(nullptr);
+    sk_sp<SkImage> simg = make(SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named));
+
+    canvas->translate(10, 10);
+    show_mips(canvas, limg.get());
+    canvas->translate(0, limg->height() + 10.0f);
+    show_mips(canvas, simg.get());
+}
+