src/core/SkPaintPriv.cpp

/*
 * Copyright 2013 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "include/core/SkPaint.h"
#include "src/core/SkColorFilterBase.h"
#include "src/core/SkColorSpacePriv.h"
#include "src/core/SkPaintPriv.h"
#include "src/core/SkXfermodePriv.h"
#include "src/shaders/SkColorFilterShader.h"
#include "src/shaders/SkShaderBase.h"

static bool changes_alpha(const SkPaint& paint) {
    SkColorFilter* cf = paint.getColorFilter();
    return cf && !as_CFB(cf)->isAlphaUnchanged();
}

bool SkPaintPriv::Overwrites(const SkPaint* paint, ShaderOverrideOpacity overrideOpacity) {
    if (!paint) {
        // No paint means we default to SRC_OVER, so we overwrite iff our shader-override
        // is opaque, or we don't have one.
        return overrideOpacity != kNotOpaque_ShaderOverrideOpacity;
    }

    SkXfermode::SrcColorOpacity opacityType = SkXfermode::kUnknown_SrcColorOpacity;

    if (!changes_alpha(*paint)) {
        const unsigned paintAlpha = paint->getAlpha();
        if (0xff == paintAlpha && overrideOpacity != kNotOpaque_ShaderOverrideOpacity &&
            (!paint->getShader() || paint->getShader()->isOpaque()))
        {
            opacityType = SkXfermode::kOpaque_SrcColorOpacity;
        } else if (0 == paintAlpha) {
            if (overrideOpacity == kNone_ShaderOverrideOpacity && !paint->getShader()) {
                opacityType = SkXfermode::kTransparentBlack_SrcColorOpacity;
            } else {
                opacityType = SkXfermode::kTransparentAlpha_SrcColorOpacity;
            }
        }
    }

    const auto bm = paint->asBlendMode();
    if (!bm) {
        return false;   // don't know for sure, so we play it safe and return false.
    }
    return SkXfermode::IsOpaque(bm.value(), opacityType);
}

bool SkPaintPriv::ShouldDither(const SkPaint& p, SkColorType dstCT) {
    // The paint dither flag can veto.
    if (!p.isDither()) {
        return false;
    }

    // We always dither 565 or 4444 when requested.
    if (dstCT == kRGB_565_SkColorType || dstCT == kARGB_4444_SkColorType) {
        return true;
    }

    // Otherwise, dither is only needed for non-const paints.
    return p.getImageFilter() || p.getMaskFilter()
        || !p.getShader() || !as_SB(p.getShader())->isConstant();
}

// return true if the paint is just a single color (i.e. not a shader). If its
// a shader, then we can't compute a const luminance for it :(
static bool just_a_color(const SkPaint& paint, SkColor* color) {
    SkColor c = paint.getColor();

    const auto* shader = as_SB(paint.getShader());
    if (shader && !shader->asLuminanceColor(&c)) {
        return false;
    }
    if (paint.getColorFilter()) {
        c = paint.getColorFilter()->filterColor(c);
    }
    if (color) {
        *color = c;
    }
    return true;
}

SkColor SkPaintPriv::ComputeLuminanceColor(const SkPaint& paint) {
    SkColor c;
    if (!just_a_color(paint, &c)) {
        c = SkColorSetRGB(0x7F, 0x80, 0x7F);
    }
    return c;
}

void SkPaintPriv::RemoveColorFilter(SkPaint* p, SkColorSpace* dstCS) {
    if (SkColorFilter* filter = p->getColorFilter()) {
        if (SkShader* shader = p->getShader()) {
            // SkColorFilterShader will modulate the shader color by paint alpha
            // before applying the filter, so we'll reset it to opaque.
            p->setShader(sk_make_sp<SkColorFilterShader>(sk_ref_sp(shader),
                                                         p->getAlphaf(),
                                                         sk_ref_sp(filter)));
            p->setAlphaf(1.0f);
        } else {
            p->setColor(filter->filterColor4f(p->getColor4f(), sk_srgb_singleton(), dstCS), dstCS);
        }
        p->setColorFilter(nullptr);
    }
}

SkScalar SkPaintPriv::ComputeResScaleForStroking(const SkMatrix& matrix) {
    // Not sure how to handle perspective differently, so we just don't try (yet)
    SkScalar sx = SkPoint::Length(matrix[SkMatrix::kMScaleX], matrix[SkMatrix::kMSkewY]);
    SkScalar sy = SkPoint::Length(matrix[SkMatrix::kMSkewX],  matrix[SkMatrix::kMScaleY]);
    if (SkScalarsAreFinite(sx, sy)) {
        SkScalar scale = std::max(sx, sy);
        if (scale > 0) {
            return scale;
        }
    }
    return 1;
}