src/core/SkRecordOpts.cpp

/*
 * Copyright 2014 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "SkRecordOpts.h"

#include "SkRecordPattern.h"
#include "SkRecords.h"
#include "SkTDArray.h"

using namespace SkRecords;

void SkRecordOptimize(SkRecord* record) {
    // This might be useful  as a first pass in the future if we want to weed
    // out junk for other optimization passes.  Right now, nothing needs it,
    // and the bounding box hierarchy will do the work of skipping no-op
    // Save-NoDraw-Restore sequences better than we can here.
    //SkRecordNoopSaveRestores(record);

    SkRecordNoopSaveLayerDrawRestores(record);
}

// Most of the optimizations in this file are pattern-based.  These are all defined as structs with:
//   - a Pattern typedef
//   - a bool onMatch(SkRceord*, Pattern*, unsigned begin, unsigned end) method,
//     which returns true if it made changes and false if not.

// Run a pattern-based optimization once across the SkRecord, returning true if it made any changes.
// It looks for spans which match Pass::Pattern, and when found calls onMatch() with the pattern,
// record, and [begin,end) span of the commands that matched.
template <typename Pass>
static bool apply(Pass* pass, SkRecord* record) {
    typename Pass::Pattern pattern;
    bool changed = false;
    unsigned begin, end = 0;

    while (pattern.search(record, &begin, &end)) {
        changed |= pass->onMatch(record, &pattern, begin, end);
    }
    return changed;
}

// Turns the logical NoOp Save and Restore in Save-Draw*-Restore patterns into actual NoOps.
struct SaveOnlyDrawsRestoreNooper {
    typedef Pattern3<Is<Save>,
                     Star<Or<Is<NoOp>, IsDraw> >,
                     Is<Restore> >
        Pattern;

    bool onMatch(SkRecord* record, Pattern* pattern, unsigned begin, unsigned end) {
        record->replace<NoOp>(begin);  // Save
        record->replace<NoOp>(end-1);  // Restore
        return true;
    }
};
// Turns logical no-op Save-[non-drawing command]*-Restore patterns into actual no-ops.
struct SaveNoDrawsRestoreNooper {
    // Star matches greedily, so we also have to exclude Save and Restore.
    // Nested SaveLayers need to be excluded, or we'll match their Restore!
    typedef Pattern3<Is<Save>,
                     Star<Not<Or4<Is<Save>,
                                  Is<SaveLayer>,
                                  Is<Restore>,
                                  IsDraw> > >,
                     Is<Restore> >
        Pattern;

    bool onMatch(SkRecord* record, Pattern* pattern, unsigned begin, unsigned end) {
        // The entire span between Save and Restore (inclusively) does nothing.
        for (unsigned i = begin; i < end; i++) {
            record->replace<NoOp>(i);
        }
        return true;
    }
};
void SkRecordNoopSaveRestores(SkRecord* record) {
    SaveOnlyDrawsRestoreNooper onlyDraws;
    SaveNoDrawsRestoreNooper noDraws;

    // Run until they stop changing things.
    while (apply(&onlyDraws, record) || apply(&noDraws, record));
}

// For some SaveLayer-[drawing command]-Restore patterns, merge the SaveLayer's alpha into the
// draw, and no-op the SaveLayer and Restore.
struct SaveLayerDrawRestoreNooper {
    typedef Pattern3<Is<SaveLayer>, IsDraw, Is<Restore> > Pattern;

    bool onMatch(SkRecord* record, Pattern* pattern, unsigned begin, unsigned end) {
        SaveLayer* saveLayer = pattern->first<SaveLayer>();
        if (saveLayer->bounds != NULL) {
            // SaveLayer with bounds is too tricky for us.
            return false;
        }

        SkPaint* layerPaint = saveLayer->paint;
        if (NULL == layerPaint) {
            // There wasn't really any point to this SaveLayer at all.
            return KillSaveLayerAndRestore(record, begin);
        }

        SkPaint* drawPaint = pattern->second<SkPaint>();
        if (drawPaint == NULL) {
            // We can just give the draw the SaveLayer's paint.
            // TODO(mtklein): figure out how to do this clearly
            return false;
        }

        const uint32_t layerColor = layerPaint->getColor();
        const uint32_t  drawColor =  drawPaint->getColor();
        if (!IsOnlyAlpha(layerColor)  || !IsOpaque(drawColor) ||
            HasAnyEffect(*layerPaint) || CantFoldAlpha(*drawPaint)) {
            // Too fancy for us.  Actually, as long as layerColor is just an alpha
            // we can blend it into drawColor's alpha; drawColor doesn't strictly have to be opaque.
            return false;
        }

        drawPaint->setColor(SkColorSetA(drawColor, SkColorGetA(layerColor)));
        return KillSaveLayerAndRestore(record, begin);
    }

    static bool KillSaveLayerAndRestore(SkRecord* record, unsigned saveLayerIndex) {
        record->replace<NoOp>(saveLayerIndex);    // SaveLayer
        record->replace<NoOp>(saveLayerIndex+2);  // Restore
        return true;
    }

    static bool HasAnyEffect(const SkPaint& paint) {
        return paint.getPathEffect()  ||
               paint.getShader()      ||
               paint.getXfermode()    ||
               paint.getMaskFilter()  ||
               paint.getColorFilter() ||
               paint.getRasterizer()  ||
               paint.getLooper()      ||
               paint.getImageFilter();
    }

    // The alpha folding can proceed if the single draw's paint has a shader,
    // path effect, mask filter and/or rasterizer.
    // TODO: most likely the looper and only some xfer modes are the hard
    // constraints
    static bool CantFoldAlpha(const SkPaint& paint) {
        return paint.getXfermode()    ||
               paint.getColorFilter() ||
               paint.getLooper()      ||
               paint.getImageFilter();
    }

    static bool IsOpaque(SkColor color) {
        return SkColorGetA(color) == SK_AlphaOPAQUE;
    }
    static bool IsOnlyAlpha(SkColor color) {
        return SK_ColorTRANSPARENT == SkColorSetA(color, SK_AlphaTRANSPARENT);
    }
};
void SkRecordNoopSaveLayerDrawRestores(SkRecord* record) {
    SaveLayerDrawRestoreNooper pass;
    apply(&pass, record);
}