src/shaders/gradients/SkLinearGradient.cpp

/*
 * Copyright 2012 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "src/shaders/gradients/SkLinearGradient.h"

#include "include/core/SkColor.h"
#include "include/core/SkColorSpace.h"
#include "include/core/SkMatrix.h"
#include "include/core/SkRefCnt.h"
#include "include/core/SkScalar.h"
#include "include/core/SkShader.h"
#include "include/effects/SkGradient.h"
#include "include/private/base/SkFloatingPoint.h"
#include "include/private/base/SkTArray.h"
#include "src/core/SkReadBuffer.h"
#include "src/core/SkWriteBuffer.h"
#include "src/shaders/SkShaderBase.h"

#include <cstdint>
#include <utility>

class SkArenaAlloc;
class SkRasterPipeline;
enum class SkTileMode;

static SkMatrix pts_to_unit_matrix(const SkPoint pts[2]) {
    SkVector    vec = pts[1] - pts[0];
    SkScalar    mag = vec.length();
    SkScalar    inv = mag ? SkScalarInvert(mag) : 0;

    vec.scale(inv);
    SkMatrix matrix;
    matrix.setSinCos(-vec.fY, vec.fX, pts[0].fX, pts[0].fY);
    matrix.postTranslate(-pts[0].fX, -pts[0].fY);
    matrix.postScale(inv, inv);
    return matrix;
}

///////////////////////////////////////////////////////////////////////////////

SkLinearGradient::SkLinearGradient(const SkPoint pts[2], const SkGradient& desc)
        : SkGradientBaseShader(desc, pts_to_unit_matrix(pts)), fStart(pts[0]), fEnd(pts[1]) {}

sk_sp<SkFlattenable> SkLinearGradient::CreateProc(SkReadBuffer& buffer) {
    SkGradientScope scope;
    SkMatrix legacyLocalMatrix, *lmPtr = nullptr;
    auto grad = scope.unflatten(buffer, &legacyLocalMatrix);
    if (!grad) {
        return nullptr;
    }
    if (!legacyLocalMatrix.isIdentity()) {
        lmPtr = &legacyLocalMatrix;
    }
    SkPoint pts[2];
    pts[0] = buffer.readPoint();
    pts[1] = buffer.readPoint();
    return SkShaders::LinearGradient(pts, *grad, lmPtr);
}

void SkLinearGradient::flatten(SkWriteBuffer& buffer) const {
    this->INHERITED::flatten(buffer);
    buffer.writePoint(fStart);
    buffer.writePoint(fEnd);
}

void SkLinearGradient::appendGradientStages(SkArenaAlloc*, SkRasterPipeline*,
                                            SkRasterPipeline*) const {
    // No extra stage needed for linear gradients.
}

SkShaderBase::GradientType SkLinearGradient::asGradient(GradientInfo* info,
                                                        SkMatrix* localMatrix) const {
    if (info) {
        commonAsAGradient(info);
        info->fPoint[0] = fStart;
        info->fPoint[1] = fEnd;
    }
    if (localMatrix) {
        *localMatrix = SkMatrix::I();
    }
    return GradientType::kLinear;
}

sk_sp<SkShader> SkShaders::LinearGradient(const SkPoint pts[2], const SkGradient& grad,
                                          const SkMatrix* lm) {
    if (!pts || !SkIsFinite((pts[1] - pts[0]).length())) {
        return nullptr;
    }

    GRADIENT_FACTORY_EARLY_EXIT(grad, lm);

    if (SkScalarNearlyZero((pts[1] - pts[0]).length(),
                           SkGradientBaseShader::kDegenerateThreshold)) {
        // Degenerate gradient, the only tricky complication is when in clamp mode, the limit of
        // the gradient approaches two half planes of solid color (first and last). However, they
        // are divided by the line perpendicular to the start and end point, which becomes undefined
        // once start and end are exactly the same, so just use the end color for a stable solution.
        return SkGradientBaseShader::MakeDegenerateGradient(grad.colors());
    }

    sk_sp<SkShader> s = sk_make_sp<SkLinearGradient>(pts, grad);
    return s->makeWithLocalMatrix(lm ? *lm : SkMatrix::I());
}

void SkRegisterLinearGradientShaderFlattenable() {
    SK_REGISTER_FLATTENABLE(SkLinearGradient);
}