Add SkTypeface::getVariationDesignParameters

This adds a way for users to query the axis parameters for a typeface.

Change-Id: Idc2ac0d84bc7ae2ca484ae410cba5b01883418e5
Reviewed-on: https://skia-review.googlesource.com/137706
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Mike Reed <reed@google.com>

3 files changed, 61 insertions, 5 deletions

diff --git a/include/core/SkFontArguments.h b/include/core/SkFontArguments.h
index 473798fb84..52f20728a1 100644
--- a/include/core/SkFontArguments.h
+++ b/include/core/SkFontArguments.h
@@ -5,8 +5,8 @@
  * found in the LICENSE file.
  */
 
-#ifndef SkFontAgruments_DEFINED
-#define SkFontAgruments_DEFINED
+#ifndef SkFontArguments_DEFINED
+#define SkFontArguments_DEFINED
 
 #include "SkScalar.h"
 #include "SkTypes.h"
@@ -16,15 +16,15 @@ struct SkFontArguments {
     struct VariationPosition {
         struct Coordinate {
             SkFourByteTag axis;
-            SkScalar value;
+            float value;
         };
         const Coordinate* coordinates;
         int coordinateCount;
     };
-    // deprecated, use VariationCoordinate instead
+    // deprecated, use VariationPosition::Coordinate instead
     struct Axis {
        SkFourByteTag fTag;
-       SkScalar fStyleValue;
+       float fStyleValue;
     };
 
     SkFontArguments() : fCollectionIndex(0), fVariationDesignPosition{nullptr, 0} {}
diff --git a/include/core/SkFontParameters.h b/include/core/SkFontParameters.h
new file mode 100644
index 0000000000..7d3c407add
--- /dev/null
+++ b/include/core/SkFontParameters.h
@@ -0,0 +1,38 @@
+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkFontParameters_DEFINED
+#define SkFontParameters_DEFINED
+
+#include "SkScalar.h"
+#include "SkTypes.h"
+
+struct SkFontParameters {
+    struct Variation {
+        // Parameters in a variation font axis.
+        struct Axis {
+            // Four character identifier of the font axis (weight, width, slant, italic...).
+            SkFourByteTag tag;
+            // Minimum value supported by this axis.
+            float min;
+            // Default value set by this axis.
+            float def;
+            // Maximum value supported by this axis. The maximum can equal the minimum.
+            float max;
+            // Return whether this axis is recommended to be remain hidden in user interfaces.
+            bool isHidden() const { return flags & HIDDEN; }
+            // Set this axis to be remain hidden in user interfaces.
+            void setHidden(bool hidden) { flags = hidden ? (flags | HIDDEN) : (flags & ~HIDDEN); }
+        private:
+            static constexpr uint16_t HIDDEN = 0x0001;
+            // Attributes for a font axis.
+            uint16_t flags;
+        };
+    };
+};
+
+#endif
diff --git a/include/core/SkTypeface.h b/include/core/SkTypeface.h
index 4118152dea..51f339ccfa 100644
--- a/include/core/SkTypeface.h
+++ b/include/core/SkTypeface.h
@@ -11,6 +11,7 @@
 #include "../private/SkOnce.h"
 #include "../private/SkWeakRefCnt.h"
 #include "SkFontArguments.h"
+#include "SkFontParameters.h"
 #include "SkFontStyle.h"
 #include "SkRect.h"
 #include "SkString.h"
@@ -71,6 +72,20 @@ public:
     int getVariationDesignPosition(SkFontArguments::VariationPosition::Coordinate coordinates[],
                                    int coordinateCount) const;
 
+    /** Copy into 'parameters' (allocated by the caller) the design variation parameters.
+     *
+     *  @param parameters the buffer into which to write the design variation parameters.
+     *  @param coordinateCount the number of entries available through 'parameters'.
+     *
+     *  @return The number of axes, or -1 if there is an error.
+     *  If 'parameters != nullptr' and 'parameterCount >= numAxes' then 'parameters' will be
+     *  filled with the variation parameters describing the position of this typeface in design
+     *  variation space. It is possible the number of axes can be retrieved but actual parameters
+     *  cannot.
+     */
+    int getVariationDesignParameters(SkFontParameters::Variation::Axis parameters[],
+                                     int parameterCount) const;
+
     /** Return a 32bit value for this typeface, unique for the underlying font
         data. Will never return 0.
      */
@@ -341,6 +356,9 @@ protected:
         SkFontArguments::VariationPosition::Coordinate coordinates[],
         int coordinateCount) const = 0;
 
+    virtual int onGetVariationDesignParameters(
+        SkFontParameters::Variation::Axis parameters[], int parameterCount) const;
+
     virtual void onGetFontDescriptor(SkFontDescriptor*, bool* isLocal) const = 0;
 
     virtual int onCharsToGlyphs(const void* chars, Encoding, SkGlyphID glyphs[],