respect srgb gamma when building mips

gm/mipmap.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gm.h"
 #include "SkCanvas.h"
 #include "SkImage.h"
 #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) {

[Brian Osman, 2016/06/10 13:37:14]

Want to make sure I understand the changes to this GM: The image returned by
make_image now contains the "same" data, encoded as either sRGB or Linear. (But
representing the same absolute brightness in both cases). Then we draw them
side-by-side, so that (in S32 mode) the only real different should be the
filtering and mip-mapping of the two sources? But in L32 mode, they will look
very different, because one of them contains linear values that are never going
to be corrected for display?

Assuming that's the intention, it might be nice to add a comment explaining
what's happening.

[reed1, 2016/06/10 14:26:04]

reverted

+    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));
 
     SkPaint paint;
     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);
 }