move SkImageInfo into its own header

include/core/SkImageInfo.h

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkImageInfo_DEFINED
+#define SkImageInfo_DEFINED
+
+#include "SkTypes.h"
+
+/**
+ *  Describes how to interpret the alpha compoent of a pixel.
+ */
+enum SkAlphaType {
+    /**
+     *  All pixels should be treated as opaque, regardless of the value stored
+     *  in their alpha field. Used for legacy images that wrote 0 or garbarge
+     *  in their alpha field, but intended the RGB to be treated as opaque.
+     */
+    kIgnore_SkAlphaType,
+    
+    /**
+     *  All pixels are stored as opaque. This differs slightly from kIgnore in
+     *  that kOpaque has correct "opaque" values stored in the pixels, while
+     *  kIgnore may not, but in both cases the caller should treat the pixels
+     *  as opaque.
+     */
+    kOpaque_SkAlphaType,
+    
+    /**
+     *  All pixels have their alpha premultiplied in their color components.
+     *  This is the natural format for the rendering target pixels.
+     */
+    kPremul_SkAlphaType,
+    
+    /**
+     *  All pixels have their color components stored without any regard to the
+     *  alpha. e.g. this is the default configuration for PNG images.
+     *
+     *  This alpha-type is ONLY supported for input images. Rendering cannot
+     *  generate this on output.
+     */
+    kUnpremul_SkAlphaType,
+    
+    kLastEnum_SkAlphaType = kUnpremul_SkAlphaType
+};
+
+static inline bool SkAlphaTypeIsOpaque(SkAlphaType at) {
+    SK_COMPILE_ASSERT(kIgnore_SkAlphaType < kOpaque_SkAlphaType, bad_alphatype_order);
+    SK_COMPILE_ASSERT(kPremul_SkAlphaType > kOpaque_SkAlphaType, bad_alphatype_order);
+    SK_COMPILE_ASSERT(kUnpremul_SkAlphaType > kOpaque_SkAlphaType, bad_alphatype_order);
+
+    return (unsigned)at <= kOpaque_SkAlphaType;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+/**
+ *  Describes how to interpret the components of a pixel.
+ */
+enum SkColorType {
+    kAlpha_8_SkColorType,
+    kRGB_565_SkColorType,
+    kRGBA_8888_SkColorType,
+    kBGRA_8888_SkColorType,
+    kIndex8_SkColorType,
+
+    kLastEnum_SkColorType = kIndex8_SkColorType,
+
+#if SK_PMCOLOR_BYTE_ORDER(B,G,R,A)
+    kPMColor_SkColorType = kBGRA_8888_SkColorType
+#elif SK_PMCOLOR_BYTE_ORDER(R,G,B,A)
+    kPMColor_SkColorType = kRGBA_8888_SkColorType
+#else
+#error "SK_*32_SHFIT values must correspond to BGRA or RGBA byte order"
+#endif
+};
+
+static int SkColorTypeBytesPerPixel(SkColorType ct) {
+    static const uint8_t gSize[] = {
+        1,  // Alpha_8
+        2,  // RGB_565
+        4,  // RGBA_8888
+        4,  // BGRA_8888
+        1,  // kIndex_8
+    };
+    SK_COMPILE_ASSERT(SK_ARRAY_COUNT(gSize) == (size_t)(kLastEnum_SkColorType + 1),
+                      size_mismatch_with_SkColorType_enum);
+
+    SkASSERT((size_t)ct < SK_ARRAY_COUNT(gSize));
+    return gSize[ct];
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+/**
+ *  Describe an image's dimensions and pixel type.
+ */
+struct SkImageInfo {
+    int         fWidth;
+    int         fHeight;
+    SkColorType fColorType;
+    SkAlphaType fAlphaType;
+
+    bool isOpaque() const {
+        return SkAlphaTypeIsOpaque(fAlphaType);
+    }
+
+    int bytesPerPixel() const {
+        return SkColorTypeBytesPerPixel(fColorType);
+    }
+
+    bool operator==(const SkImageInfo& other) const {
+        return 0 == memcmp(this, &other, sizeof(other));
+    }
+    bool operator!=(const SkImageInfo& other) const {
+        return 0 != memcmp(this, &other, sizeof(other));
+    }
+};
+
+#endif