MacViews: draw combobox arrow backgrounds

ui/native_theme/native_theme_mac.mm

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/native_theme/native_theme_mac.h"
 
 #import <Cocoa/Cocoa.h>
 #include <stddef.h>
 
 #include "base/mac/mac_util.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/mac/sdk_forward_declarations.h"
 #include "base/macros.h"
 #import "skia/ext/skia_utils_mac.h"
+#include "third_party/skia/include/core/SkRRect.h"
 #include "third_party/skia/include/effects/SkGradientShader.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/skia_util.h"
 #include "ui/native_theme/common_theme.h"
 
 namespace {
 
 // Values calculated by reading pixels and solving simultaneous equations
 // derived from "A over B" alpha compositing. Steps: Sample the semi-transparent
 // pixel over two backgrounds; P1, P2 over backgrounds B1, B2. Use the color
@@ skipping 234 matching lines @@
       // and is a good shade of gray, it's not blue enough for the Blue theme.
       paint.setColor(GetSystemColor(kColorId_HoverMenuItemBackgroundColor));
       canvas->drawRect(gfx::RectToSkRect(rect), paint);
       break;
     default:
       NOTREACHED();
       break;
   }
 }
 
+skia::RefPtr<SkShader>
+GetComboboxArrowBackgroundShader(NativeTheme::State state, int height) {
+  SkPoint gradient_points[2];
+  gradient_points[0].iset(0, 0);
+  gradient_points[1].iset(0, height);
+
+  // TODO(ellyjones): These colors are not exactly right, and the gradient
+  // probably needs more stops.
+  SkScalar gradient_positions[] = { 0.0, 0.38, 1.0 };
+
+  SkColor light_blue = SkColorSetRGB(0x4e, 0x97, 0xfd);

[tapted, 2016/03/21 07:09:04]

Are there things we can pick from ui/gfx/color_palette.h? The mocks we got are
meant to be inspired by MD colors, so it might be something from this list
(otherwise we should maybe add it, since it might be an "official" color

[Elly Fong-Jones, 2016/03/21 18:53:56]

Done. kGoogleBlue300 and kGoogleBlue700 turn out to produce a pleasing gradient.

+  SkColor dark_blue = SkColorSetRGB(0x3f, 0x68, 0xe5);
+
+  // TODO(ellyjones): Does this need to handle states other than kHovered and
+  // kNormal?

[tapted, 2016/03/21 07:09:04]

kDisabled. There's also "invalid"

[Elly Fong-Jones, 2016/03/21 18:53:56]

Done.

+  SkColor hovered_colors[] = { light_blue, light_blue, dark_blue };
+  SkColor normal_colors[] = { SK_ColorWHITE, SK_ColorWHITE, SK_ColorWHITE };
+  SkColor* gradient_colors = state == NativeTheme::kHovered ?
+                             hovered_colors :
+                             normal_colors;
+
+  skia::RefPtr<SkShader> gradient_shader = skia::AdoptRef(
+      SkGradientShader::CreateLinear(
+          gradient_points, gradient_colors, gradient_positions, 3,
+          SkShader::kClamp_TileMode));
+  return gradient_shader;
+}
+
+void NativeThemeMac::PaintComboboxArrowBackground(SkCanvas* canvas,
+                                                  State state,
+                                                  const gfx::Rect& rect) const {
+  // TODO(ellyjones): This constant is duplicated in FocusableRoundedBorder at
+  // the moment. Maybe this function should take this as a parameter instead.
+  const int kComboboxBorderRadius = 5;
+
+  skia::RefPtr<SkShader> shader =
+      GetComboboxArrowBackgroundShader(state, rect.height());
+
+  SkPaint paint;
+  paint.setShader(shader.get());
+  paint.setStyle(SkPaint::kFill_Style);
+  paint.setAntiAlias(true);
+
+  SkPoint no_curve = SkPoint::Make(0, 0);
+  SkPoint curve = SkPoint::Make(kComboboxBorderRadius, kComboboxBorderRadius);
+  // Curve upper-right and lower-right corners of the background only.
+  SkVector curves[4] = { no_curve, curve, curve, no_curve };
+
+  SkRRect fill_rect;
+  fill_rect.setRectRadii(gfx::RectToSkRect(rect), curves);
+
+  canvas->drawRRect(fill_rect, paint);
+}
+
 NativeThemeMac::NativeThemeMac() {
 }
 
 NativeThemeMac::~NativeThemeMac() {
 }
 
 }  // namespace ui