skia2/src/core/SkImageInfoPriv.h

/*
 * Copyright 2017 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

/**
 *  Returns true if |info| contains a valid combination of width, height, colorType, alphaType,
 *  colorSpace.  Returns false otherwise.
 */
static inline bool SkImageInfoIsValid(const SkImageInfo& info) {
    if (info.width() <= 0 || info.height() <= 0) {
        return false;
    }

    if (kUnknown_SkColorType == info.colorType() || kUnknown_SkAlphaType == info.alphaType()) {
        return false;
    }

    if (kOpaque_SkAlphaType != info.alphaType() &&
       (kRGB_565_SkColorType == info.colorType() || kGray_8_SkColorType == info.colorType())) {
        return false;
    }

    if (kRGBA_F16_SkColorType == info.colorType() &&
       (!info.colorSpace() || !info.colorSpace()->gammaIsLinear())) {
        return false;
    }

    if (info.colorSpace() &&
       (!info.colorSpace()->gammaCloseToSRGB() && !info.colorSpace()->gammaIsLinear())) {
        return false;
    }

    return true;
}

/**
 *  Returns true if Skia has defined a pixel conversion from the |src| to the |dst|.
 *  Returns false otherwise.  Some discussion of false cases:
 *      We will not convert to kIndex8 when the |src| is not kIndex8.
 *      We do not convert to kGray8 when the |src| is not kGray8.  We may add this
 *      feature - it just requires some work to convert to luminance while handling color
 *      spaces correctly.  Currently no one is asking for this.
 *      We will not convert from kAlpha8 when the |dst| is not kAlpha8.  This would require
 *      inventing color information.
 *      We will not convert to kOpaque when the |src| is not kOpaque.  This could be
 *      implemented to set all the alpha values to 1, but there is still some ambiguity -
 *      should we use kPremul or kUnpremul color values with the opaque alphas?  Or should
 *      we just use whatever the |src| alpha is?  In the future, we could choose to clearly
 *      define this, but currently no one is asking for this feature.
 */
static inline bool SkImageInfoValidConversion(const SkImageInfo& dst, const SkImageInfo& src) {
    if (!SkImageInfoIsValid(dst) || !SkImageInfoIsValid(src)) {
        return false;
    }

    if (kIndex_8_SkColorType == dst.colorType() && kIndex_8_SkColorType != src.colorType()) {
        return false;
    }

    if (kGray_8_SkColorType == dst.colorType() && kGray_8_SkColorType != src.colorType()) {
        return false;
    }

    if (kAlpha_8_SkColorType != dst.colorType() && kAlpha_8_SkColorType == src.colorType()) {
        return false;
    }

    // TODO (msarett): This is diabled for crbug.com/683787.  How should we handle this case?
    //if (kOpaque_SkAlphaType == dst.alphaType() && kOpaque_SkAlphaType != src.alphaType()) {
    //    return false;
    //}

    return true;
}