Compile all fiddle examples locally

Motivation: it would be a good idea if the API documentation examples
were checked into the skia repository, so we could make sure they
compile as part of the commit queue.

Fiddle would make/update a named fiddle each time it gets a new
commit of Skia, extracted from the code in the examples/ directory.
The docs would point at those named fiddles.  Named fiddles have urls
in the form:

    https://fiddle.skia.org/c/@Bitmap_000

Then we would stick a link to the example into the header documentation
like this:

    /** Allocates the pixel memory for the bitmap, given its dimensions
        and SkColorType. Returns true on success, where success means
        either setPixels() or setPixelRef() was called.

        @param bitmap  SkBitmap containing SkImageInfo as input, and
                       SkPixelRef as output
        @return        true if SkPixelRef was allocated

        @example       https://fiddle.skia.org/c/@Bitmap_000
    */
    bool allocPixelRef(SkBitmap* bitmap) override;

There are still around 200 disabled examples that need to be fixed
(these result from API changes since the author left).

Change-Id: I14a31348a9ccaaa31f65424b91e3a3533d2583a7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/198824
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
diff --git a/docs/examples/ImageInfo_012.cpp b/docs/examples/ImageInfo_012.cpp
new file mode 100644
index 0000000..0ab5ee3
--- /dev/null
+++ b/docs/examples/ImageInfo_012.cpp
@@ -0,0 +1,52 @@
+// Copyright 2019 Google LLC.
+// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
+#include "fiddle/examples.h"
+// HASH=dd81527bbdf5eaae7dd21ac04ab84f9e
+REG_FIDDLE(ImageInfo_012, 256, 96, false, 0) {
+union FloatUIntUnion {
+    uint32_t fUInt;
+    float    fFloat;
+};
+uint16_t FloatToHalf(float f) {
+    static const FloatUIntUnion magic = { 15 << 23 };
+    static const uint32_t round_mask = ~0xfffu;
+    FloatUIntUnion floatUnion;
+    floatUnion.fFloat = f;
+    uint32_t sign = floatUnion.fUInt & 0x80000000u;
+    floatUnion.fUInt ^= sign;
+    floatUnion.fUInt &= round_mask;
+    floatUnion.fFloat *= magic.fFloat;
+    floatUnion.fUInt -= round_mask;
+    return (floatUnion.fUInt >> 13) | (sign >> 16);
+}
+
+void draw(SkCanvas* canvas) {
+    canvas->scale(16, 16);
+    SkBitmap bitmap;
+    SkImageInfo imageInfo = SkImageInfo::Make(2, 2, kRGBA_F16_SkColorType, kPremul_SkAlphaType);
+    bitmap.allocPixels(imageInfo);
+    SkCanvas offscreen(bitmap);
+    offscreen.clear(SK_ColorGREEN);
+    canvas->drawBitmap(bitmap, 0, 0);
+    auto H = [](float c) -> uint16_t {
+        return FloatToHalf(c);
+    };
+                             //     R        G        B        A
+    uint16_t red_f16[][4] =  { { H(1.0), H(0.0), H(0.0), H(1.0) },
+                               { H(.75), H(0.0), H(0.0), H(1.0) },
+                               { H(.50), H(0.0), H(0.0), H(1.0) },
+                               { H(.25), H(0.0), H(0.0), H(1.0) } };
+    uint16_t blue_f16[][4] = { { H(0.0), H(0.0), H(1.0), H(1.0) },
+                               { H(0.0), H(0.0), H(.75), H(1.0) },
+                               { H(0.0), H(0.0), H(.50), H(1.0) },
+                               { H(0.0), H(0.0), H(.25), H(1.0) } };
+    SkPixmap redPixmap(imageInfo, red_f16, imageInfo.minRowBytes());
+    if (bitmap.writePixels(redPixmap, 0, 0)) {
+        canvas->drawBitmap(bitmap, 2, 2);
+    }
+    SkPixmap bluePixmap(imageInfo, blue_f16, imageInfo.minRowBytes());
+    if (bitmap.writePixels(bluePixmap, 0, 0)) {
+        canvas->drawBitmap(bitmap, 4, 4);
+    }
+}
+}  // END FIDDLE