skia2/include/core/SkAlpha.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 SkAlpha_DEFINED
#define SkAlpha_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) {
    return (unsigned)at <= kOpaque_SkAlphaType;
}
#endif