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// Copyright 2019 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 <AppKit/AppKit.h>
#include <MediaAccessibility/MediaAccessibility.h>
#include "base/mac/foundation_util.h"
#include "base/mac/scoped_cftyperef.h"
#include "base/mac/scoped_nsobject.h"
#include "base/strings/stringprintf.h"
#include "base/strings/sys_string_conversions.h"
#include "skia/ext/skia_utils_mac.h"
#include "ui/gfx/color_utils.h"
#include "ui/native_theme/caption_style.h"
namespace ui {
namespace {
constexpr auto kUserDomain = kMACaptionAppearanceDomainUser;
// Each of these functions returns a MediaAccessibility (MA) default value as a
// CSS specifier string whose format is appropriate to the property. Some notes
// about these:
// 1) The behavior of MA properties (applies only as a default vs mandatory)
// is ignored deliberately at the moment; there's no good way to express
// this tri-state behavior in CSS and CaptionStyle doesn't support it on
// other platforms. All the MA properties are treated as defaults here.
// 2) The MA "window" concept is not implemented at all; it doesn't exist in
// CaptionStyle or in the Blink-side WebVTT implementation.
// 3) If a function is confused about how to map the system value to a Blink
// WebVTT attribute (or a CSS specifier), it's always safe to return an
// empty string, which will cause Blink to fall back to its default
// behavior for that attribute.
// 4) The only useful domain to retrieve attributes from is kUserDomain; the
// system domain's values never change.
std::string GetMAForegroundColorAsCSSColor() {
base::ScopedCFTypeRef<CGColorRef> cg_color(
MACaptionAppearanceCopyForegroundColor(kUserDomain, nullptr));
return color_utils::SkColorToRgbaString(
std::string GetMABackgroundColorAsCSSColor() {
base::ScopedCFTypeRef<CGColorRef> cg_color(
MACaptionAppearanceCopyBackgroundColor(kUserDomain, nullptr));
return color_utils::SkColorToRgbaString(
// The MA text scale is a float between 0.0 and 2.0; this function converts it
// to a CSS string specifying a percentage to scale the text by.
std::string GetMATextScaleAsCSSPercent() {
int percent =
100 * MACaptionAppearanceGetRelativeCharacterSize(kUserDomain, nullptr);
return base::StringPrintf("%d%%", percent);
std::string GetMATextEdgeStyleAsCSSShadow() {
MACaptionAppearanceTextEdgeStyle style =
MACaptionAppearanceGetTextEdgeStyle(kUserDomain, nullptr);
// The MACaptionAppearanceTextEdgeStyle -> CSS shadow specs in this function
// were found by experimentation and eyeballing - there's no known
// documentation of how the MA shadow constants are supposed to look.
switch (style) {
case kMACaptionAppearanceTextEdgeStyleUndefined:
case kMACaptionAppearanceTextEdgeStyleNone:
// It's not clear when Undefined can be returned - here it's simply
// treated as a synonym for None.
return "";
case kMACaptionAppearanceTextEdgeStyleRaised:
return "-2px -2px 4px rgba(0, 0, 0, 0.5)";
case kMACaptionAppearanceTextEdgeStyleDepressed:
return "2px 2px 4px rgba(0, 0, 0, 0.5)";
case kMACaptionAppearanceTextEdgeStyleUniform:
// This system style looks like a 2px black stroke drawn around the edge
// of the text. This isn't doable using CSS shadows, but drawing black
// shadows around all the edges of the text produces a reasonable
// imitation.
return "-1px 0px 0px black, 0px -1px 0px black, "
" 1px 0px 0px black, 0px 1px 0px black";
case kMACaptionAppearanceTextEdgeStyleDropShadow:
// Compose a pair of shadows to create the "drop" effect - a
// semi-transparent shadow around the text, then a darker shadow below and
// to the right of it.
return "0px 0px 2px rgba(0, 0, 0, 0.5), 2px 2px 2px black";
// Thankfully, CSS font descriptors can simply use font names understood by the
// platform, so that's what this function does. It only returns attributes for
// the default font. The system allows configuring default font variants for
// each font face to be used in WebVTT captions, which is not implemented here.
void GetMAFontAsCSSFontSpecifiers(std::string* font_family,
std::string* font_variant) {
base::ScopedCFTypeRef<CTFontDescriptorRef> ct_font_desc(
kUserDomain, nullptr, kMACaptionAppearanceFontStyleDefault));
base::ScopedCFTypeRef<CFStringRef> ct_font_family_name(
ct_font_desc, kCTFontFamilyNameAttribute)));
if (ct_font_family_name)
*font_family = base::SysCFStringRefToUTF8(ct_font_family_name);
base::ScopedCFTypeRef<CFStringRef> ct_font_face_name(
CTFontDescriptorCopyAttribute(ct_font_desc, kCTFontNameAttribute)));
if (ct_font_face_name)
*font_variant = base::SysCFStringRefToUTF8(ct_font_face_name);
} // namespace
// static
CaptionStyle CaptionStyle::FromSystemSettings() {
CaptionStyle style;
style.text_color = GetMAForegroundColorAsCSSColor();
style.background_color = GetMABackgroundColorAsCSSColor();
style.text_size = GetMATextScaleAsCSSPercent();
style.text_shadow = GetMATextEdgeStyleAsCSSShadow();
GetMAFontAsCSSFontSpecifiers(&style.font_family, &style.font_variant);
return style;
} // namespace ui