src/core/SkComposeShader.cpp

/*
 * Copyright 2006 The Android Open Source Project
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */


#include "SkComposeShader.h"
#include "SkColorFilter.h"
#include "SkColorPriv.h"
#include "SkColorShader.h"
#include "SkFlattenableBuffers.h"
#include "SkXfermode.h"
#include "SkString.h"

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

SkComposeShader::SkComposeShader(SkShader* sA, SkShader* sB, SkXfermode* mode) {
    fShaderA = sA;  sA->ref();
    fShaderB = sB;  sB->ref();
    // mode may be null
    fMode = mode;
    SkSafeRef(mode);
}

SkComposeShader::SkComposeShader(SkFlattenableReadBuffer& buffer) :
    INHERITED(buffer) {
    fShaderA = buffer.readFlattenableT<SkShader>();
    if (NULL == fShaderA) {
        fShaderA = SkNEW_ARGS(SkColorShader, (0));
    }
    fShaderB = buffer.readFlattenableT<SkShader>();
    if (NULL == fShaderB) {
        fShaderB = SkNEW_ARGS(SkColorShader, (0));
    }
    fMode = buffer.readFlattenableT<SkXfermode>();
}

SkComposeShader::~SkComposeShader() {
    SkSafeUnref(fMode);
    fShaderB->unref();
    fShaderA->unref();
}

class SkAutoAlphaRestore {
public:
    SkAutoAlphaRestore(SkPaint* paint, uint8_t newAlpha) {
        fAlpha = paint->getAlpha();
        fPaint = paint;
        paint->setAlpha(newAlpha);
    }

    ~SkAutoAlphaRestore() {
        fPaint->setAlpha(fAlpha);
    }
private:
    SkPaint*    fPaint;
    uint8_t     fAlpha;
};

void SkComposeShader::flatten(SkFlattenableWriteBuffer& buffer) const {
    this->INHERITED::flatten(buffer);
    buffer.writeFlattenable(fShaderA);
    buffer.writeFlattenable(fShaderB);
    buffer.writeFlattenable(fMode);
}

/*  We call setContext on our two worker shaders. However, we
    always let them see opaque alpha, and if the paint really
    is translucent, then we apply that after the fact.

    We need to keep the calls to setContext/endContext balanced, since if we
    return false, our endContext() will not be called.
 */
bool SkComposeShader::setContext(const SkBitmap& device,
                                 const SkPaint& paint,
                                 const SkMatrix& matrix) {
    if (!this->INHERITED::setContext(device, paint, matrix)) {
        return false;
    }

    // we preconcat our localMatrix (if any) with the device matrix
    // before calling our sub-shaders

    SkMatrix tmpM;

    tmpM.setConcat(matrix, this->getLocalMatrix());

    SkAutoAlphaRestore  restore(const_cast<SkPaint*>(&paint), 0xFF);

    bool setContextA = fShaderA->setContext(device, paint, tmpM);
    bool setContextB = fShaderB->setContext(device, paint, tmpM);
    if (!setContextA || !setContextB) {
        if (setContextB) {
            fShaderB->endContext();
        }
        else if (setContextA) {
            fShaderA->endContext();
        }
        this->INHERITED::endContext();
        return false;
    }
    return true;
}

void SkComposeShader::endContext() {
    fShaderB->endContext();
    fShaderA->endContext();
    this->INHERITED::endContext();
}

// larger is better (fewer times we have to loop), but we shouldn't
// take up too much stack-space (each element is 4 bytes)
#define TMP_COLOR_COUNT     64

void SkComposeShader::shadeSpan(int x, int y, SkPMColor result[], int count) {
    SkShader*   shaderA = fShaderA;
    SkShader*   shaderB = fShaderB;
    SkXfermode* mode = fMode;
    unsigned    scale = SkAlpha255To256(this->getPaintAlpha());

    SkPMColor   tmp[TMP_COLOR_COUNT];

    if (NULL == mode) {   // implied SRC_OVER
        // TODO: when we have a good test-case, should use SkBlitRow::Proc32
        // for these loops
        do {
            int n = count;
            if (n > TMP_COLOR_COUNT) {
                n = TMP_COLOR_COUNT;
            }

            shaderA->shadeSpan(x, y, result, n);
            shaderB->shadeSpan(x, y, tmp, n);

            if (256 == scale) {
                for (int i = 0; i < n; i++) {
                    result[i] = SkPMSrcOver(tmp[i], result[i]);
                }
            } else {
                for (int i = 0; i < n; i++) {
                    result[i] = SkAlphaMulQ(SkPMSrcOver(tmp[i], result[i]),
                                            scale);
                }
            }

            result += n;
            x += n;
            count -= n;
        } while (count > 0);
    } else {    // use mode for the composition
        do {
            int n = count;
            if (n > TMP_COLOR_COUNT) {
                n = TMP_COLOR_COUNT;
            }

            shaderA->shadeSpan(x, y, result, n);
            shaderB->shadeSpan(x, y, tmp, n);
            mode->xfer32(result, tmp, n, NULL);

            if (256 == scale) {
                for (int i = 0; i < n; i++) {
                    result[i] = SkAlphaMulQ(result[i], scale);
                }
            }

            result += n;
            x += n;
            count -= n;
        } while (count > 0);
    }
}

#ifdef SK_DEVELOPER
void SkComposeShader::toString(SkString* str) const {
    str->append("SkComposeShader: (");

    str->append("ShaderA: ");
    fShaderA->toString(str);
    str->append(" ShaderB: ");
    fShaderB->toString(str);
    str->append(" Xfermode: ");
    // TODO: add "fMode->toString(str);" once SkXfermode::toString is added

    this->INHERITED::toString(str);

    str->append(")");
}
#endif