experimental/pathkit/pathkit_wasm_bindings.cpp

/*
 * Copyright 2018 Google LLC
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "SkFloatBits.h"
#include "SkFloatingPoint.h"
#include "SkMatrix.h"
#include "SkParsePath.h"
#include "SkPath.h"
#include "SkPathOps.h"
#include "SkRect.h"
#include "SkString.h"

#include <emscripten/emscripten.h>
#include <emscripten/bind.h>

using namespace emscripten;

static const int MOVE = 0;
static const int LINE = 1;
static const int QUAD = 2;
static const int CUBIC = 4;
static const int CLOSE = 5;

// Just for self-documenting purposes where the main thing being returned is an
// SkPath, but in an error case, something of type val (e.g. null) could also be
// returned;
using SkPathOrVal = emscripten::val;

// =================================================================================
// Creating/Exporting Paths with cmd arrays
// =================================================================================

template <typename VisitFunc>
void VisitPath(const SkPath& p, VisitFunc&& f) {
    SkPath::RawIter iter(p);
    SkPoint pts[4];
    SkPath::Verb verb;
    while ((verb = iter.next(pts)) != SkPath::kDone_Verb) {
        f(verb, pts, iter);
    }
}

emscripten::val EMSCRIPTEN_KEEPALIVE ToCmds(const SkPath& path) {
    emscripten::val cmds = emscripten::val::array();

    VisitPath(path, [&cmds](SkPath::Verb verb, const SkPoint pts[4], SkPath::RawIter iter) {
        emscripten::val cmd = emscripten::val::array();
        switch (verb) {
        case SkPath::kMove_Verb:
            cmd.call<void>("push", MOVE, pts[0].x(), pts[0].y());
            break;
        case SkPath::kLine_Verb:
            cmd.call<void>("push", LINE, pts[1].x(), pts[1].y());
            break;
        case SkPath::kQuad_Verb:
            cmd.call<void>("push", QUAD, pts[1].x(), pts[1].y(), pts[2].x(), pts[2].y());
            break;
        case SkPath::kConic_Verb:
            SkPoint quads[5];
            // approximate with 2^1=2 quads.
            SkPath::ConvertConicToQuads(pts[0], pts[1], pts[2], iter.conicWeight(), quads, 1);
            cmd.call<void>("push", MOVE, quads[0].x(), quads[0].y());
            cmds.call<void>("push", cmd);
            cmd = emscripten::val::array();
            cmd.call<void>("push", QUAD, quads[1].x(), quads[1].y(), quads[2].x(), quads[2].y());
            cmds.call<void>("push", cmd);
            cmd = emscripten::val::array();
            cmd.call<void>("push", QUAD, quads[3].x(), quads[3].y(), quads[4].x(), quads[4].y());
            break;
        case SkPath::kCubic_Verb:
            cmd.call<void>("push", CUBIC,
                           pts[1].x(), pts[1].y(),
                           pts[2].x(), pts[2].y(),
                           pts[3].x(), pts[3].y());
            break;
        case SkPath::kClose_Verb:
            cmd.call<void>("push", CLOSE);
            break;
        case SkPath::kDone_Verb:
            SkASSERT(false);
            break;
        }
        cmds.call<void>("push", cmd);
    });
    return cmds;
}

// This type signature is a mess, but it's necessary. See, we can't use "bind" (EMSCRIPTEN_BINDINGS)
// and pointers to primitive types (Only bound types like SkPoint). We could if we used
// cwrap (see https://becominghuman.ai/passing-and-returning-webassembly-array-parameters-a0f572c65d97)
// but that requires us to stick to C code and, AFAIK, doesn't allow us to return nice things like
// SkPath or SkOpBuilder.
//
// So, basically, if we are using C++ and EMSCRIPTEN_BINDINGS, we can't have primative pointers
// in our function type signatures. (this gives an error message like "Cannot call foo due to unbound
// types Pi, Pf").  But, we can just pretend they are numbers and cast them to be pointers and
// the compiler is happy.
SkPathOrVal EMSCRIPTEN_KEEPALIVE FromCmds(uintptr_t /* float* */ cptr, int numCmds) {
    const auto* cmds = reinterpret_cast<const float*>(cptr);
    SkPath path;
    float x1, y1, x2, y2, x3, y3;

    // if there are not enough arguments, bail with the path we've constructed so far.
    #define CHECK_NUM_ARGS(n) \
        if ((i + n) > numCmds) { \
            SkDebugf("Not enough args to match the verbs. Saw %d commands\n", numCmds); \
            return emscripten::val::null(); \
        }

    for(int i = 0; i < numCmds;){
         switch (sk_float_floor2int(cmds[i++])) {
            case MOVE:
                CHECK_NUM_ARGS(2);
                x1 = cmds[i++], y1 = cmds[i++];
                path.moveTo(x1, y1);
                break;
            case LINE:
                CHECK_NUM_ARGS(2);
                x1 = cmds[i++], y1 = cmds[i++];
                path.lineTo(x1, y1);
                break;
            case QUAD:
                CHECK_NUM_ARGS(4);
                x1 = cmds[i++], y1 = cmds[i++];
                x2 = cmds[i++], y2 = cmds[i++];
                path.quadTo(x1, y1, x2, y2);
                break;
            case CUBIC:
                CHECK_NUM_ARGS(6);
                x1 = cmds[i++], y1 = cmds[i++];
                x2 = cmds[i++], y2 = cmds[i++];
                x3 = cmds[i++], y3 = cmds[i++];
                path.cubicTo(x1, y1, x2, y2, x3, y3);
                break;
            case CLOSE:
                path.close();
                break;
            default:
                SkDebugf("  path: UNKNOWN command %f, aborting dump...\n", cmds[i-1]);
                return emscripten::val::null();
        }
    }

    #undef CHECK_NUM_ARGS

    return emscripten::val(path);
}

SkPath EMSCRIPTEN_KEEPALIVE NewPath() {
    return SkPath();
}

//========================================================================================
// SVG things
//========================================================================================

emscripten::val EMSCRIPTEN_KEEPALIVE ToSVGString(const SkPath& path) {
    SkString s;
    SkParsePath::ToSVGString(path, &s);
    // Wrapping it in val automatically turns it into a JS string.
    // Not too sure on performance implications, but is is simpler than
    // returning a raw pointer to const char * and then using
    // Pointer_stringify() on the calling side.
    return emscripten::val(s.c_str());
}


SkPathOrVal EMSCRIPTEN_KEEPALIVE FromSVGString(std::string str) {
    SkPath path;
    if (SkParsePath::FromSVGString(str.c_str(), &path)) {
        return emscripten::val(path);
    }
    return emscripten::val::null();
}

//========================================================================================
// PATHOP things
//========================================================================================

SkPathOrVal EMSCRIPTEN_KEEPALIVE SimplifyPath(const SkPath& path) {
    SkPath simple;
    if (Simplify(path, &simple)) {
        return emscripten::val(simple);
    }
    return emscripten::val::null();
}

SkPathOrVal EMSCRIPTEN_KEEPALIVE ApplyPathOp(const SkPath& pathOne, const SkPath& pathTwo, SkPathOp op) {
    SkPath path;
    if (Op(pathOne, pathTwo, op, &path)) {
        return emscripten::val(path);
    }
    return emscripten::val::null();
}

SkPathOrVal EMSCRIPTEN_KEEPALIVE ResolveBuilder(SkOpBuilder& builder) {
    SkPath path;
    if (builder.resolve(&path)) {
        return emscripten::val(path);
    }
    return emscripten::val::null();
}

//========================================================================================
// Canvas things
//========================================================================================

void EMSCRIPTEN_KEEPALIVE ToCanvas(const SkPath& path, emscripten::val /* Path2D or Canvas*/ ctx) {
    SkPath::Iter iter(path, false);
    SkPoint pts[4];
    SkPath::Verb verb;
    while ((verb = iter.next(pts, false)) != SkPath::kDone_Verb) {
        switch (verb) {
            case SkPath::kMove_Verb:
                ctx.call<void>("moveTo", pts[0].x(), pts[0].y());
                break;
            case SkPath::kLine_Verb:
                ctx.call<void>("lineTo", pts[1].x(), pts[1].y());
                break;
            case SkPath::kQuad_Verb:
                ctx.call<void>("quadraticCurveTo", pts[1].x(), pts[1].y(), pts[2].x(), pts[2].y());
                break;
            case SkPath::kConic_Verb:
                SkPoint quads[5];
                // approximate with 2^1=2 quads.
                SkPath::ConvertConicToQuads(pts[0], pts[1], pts[2], iter.conicWeight(), quads, 1);
                ctx.call<void>("moveTo", quads[0].x(), quads[0].y());
                ctx.call<void>("quadraticCurveTo", quads[1].x(), quads[1].y(), quads[2].x(), quads[2].y());
                ctx.call<void>("quadraticCurveTo", quads[3].x(), quads[3].y(), quads[4].x(), quads[4].y());
                break;
            case SkPath::kCubic_Verb:
                ctx.call<void>("bezierCurveTo", pts[1].x(), pts[1].y(), pts[2].x(), pts[2].y(),
                                                   pts[3].x(), pts[3].y());
                break;
            case SkPath::kClose_Verb:
                ctx.call<void>("closePath");
                break;
            case SkPath::kDone_Verb:
                break;
        }
    }
}

emscripten::val JSPath2D = emscripten::val::global("Path2D");

emscripten::val EMSCRIPTEN_KEEPALIVE ToPath2D(const SkPath& path) {
    emscripten::val retVal = JSPath2D.new_();
    ToCanvas(path, retVal);
    return retVal;
}

// ======================================================================================
// Path2D API things
// ======================================================================================
void Path2DAddRect(SkPath& path, SkScalar x, SkScalar y, SkScalar width, SkScalar height) {
    path.addRect(x, y, x+width, y+height);
}

void Path2DAddArc(SkPath& path, SkScalar x, SkScalar y, SkScalar radius,
                  SkScalar startAngle, SkScalar endAngle, bool ccw) {
    SkPath temp;
    SkRect bounds = SkRect::MakeLTRB(x-radius, y-radius, x+radius, y+radius);
    const auto sweep = SkRadiansToDegrees(endAngle - startAngle) - 360 * ccw;
    temp.addArc(bounds, SkRadiansToDegrees(startAngle), sweep);
    path.addPath(temp, SkPath::kExtend_AddPathMode);
}

void Path2DAddArc(SkPath& path, SkScalar x, SkScalar y, SkScalar radius,
                  SkScalar startAngle, SkScalar endAngle) {
    Path2DAddArc(path, x, y, radius, startAngle, endAngle, false);
}

void Path2DAddEllipse(SkPath& path, SkScalar x, SkScalar y, SkScalar radiusX, SkScalar radiusY,
                     SkScalar rotation, SkScalar startAngle, SkScalar endAngle, bool ccw) {
    // This is easiest to do by making a new path and then extending the current path
    // (this properly catches the cases of if there's a moveTo before this call or not).
    SkRect bounds = SkRect::MakeLTRB(x-radiusX, y-radiusY, x+radiusX, y+radiusY);
    SkPath temp;
    const auto sweep = SkRadiansToDegrees(endAngle - startAngle) - (360 * ccw);
    temp.addArc(bounds, SkRadiansToDegrees(startAngle), sweep);

    SkMatrix m;
    m.setRotate(SkRadiansToDegrees(rotation), x, y);
    path.addPath(temp, m, SkPath::kExtend_AddPathMode);
}

void Path2DAddEllipse(SkPath& path, SkScalar x, SkScalar y, SkScalar radiusX, SkScalar radiusY,
                     SkScalar rotation, SkScalar startAngle, SkScalar endAngle) {
    Path2DAddEllipse(path, x, y, radiusX, radiusY, rotation, startAngle, endAngle, false);
}

void Path2DAddPath(SkPath& orig, const SkPath& newPath) {
    orig.addPath(newPath);
}

void Path2DAddPath(SkPath& orig, const SkPath& newPath, emscripten::val /* SVGMatrix*/ t) {
    SkMatrix m = SkMatrix::MakeAll(
                     t["a"].as<SkScalar>(), t["c"].as<SkScalar>(), t["e"].as<SkScalar>(),
                     t["b"].as<SkScalar>(), t["d"].as<SkScalar>(), t["f"].as<SkScalar>(),
                     0                    , 0                    , 1);
    orig.addPath(newPath, m);
}

// Mimics the order of SVGMatrix, just w/o the SVG Matrix
// This order is scaleX, skewY, skewX, scaleY, transX, transY
// https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/transform#Transform_functions
void Path2DAddPath(SkPath& orig, const SkPath& newPath, SkScalar a, SkScalar b, SkScalar c, SkScalar d, SkScalar e, SkScalar f) {
    SkMatrix m = SkMatrix::MakeAll(a, c, e,
                                   b, d, f,
                                   0, 0, 1);
    orig.addPath(newPath, m);
}

// Allows for full matix control.
void Path2DAddPath(SkPath& orig, const SkPath& newPath,
                   SkScalar scaleX, SkScalar skewX,  SkScalar transX,
                   SkScalar skewY,  SkScalar scaleY, SkScalar transY,
                   SkScalar pers0, SkScalar pers1, SkScalar pers2) {
    SkMatrix m = SkMatrix::MakeAll(scaleX, skewX , transX,
                                   skewY , scaleY, transY,
                                   pers0 , pers1 , pers2);
    orig.addPath(newPath, m);
}

//========================================================================================
// Testing things
//========================================================================================

// The use case for this is on the JS side is something like:
//     PathKit.SkBits2FloatUnsigned(parseInt("0xc0a00000"))
// to have precise float values for tests. In the C++ tests, we can use SkBits2Float because
// it takes int32_t, but the JS parseInt basically returns an unsigned int. So, we add in
// this helper which casts for us on the way to SkBits2Float.
float SkBits2FloatUnsigned(uint32_t floatAsBits) {
    return SkBits2Float((int32_t) floatAsBits);
}

// Binds the classes to the JS
//
// See https://kripken.github.io/emscripten-site/docs/porting/connecting_cpp_and_javascript/embind.html#non-member-functions-on-the-javascript-prototype
// for more on binding non-member functions to the JS object, allowing us to rewire
// various functions.  That is, we can make the SkPath we expose appear to have methods
// that the original SkPath does not, like rect(x, y, width, height) and toPath2D().
//
// An important detail for binding non-member functions is that the first argument
// must be SkPath& (the reference part is very important).
EMSCRIPTEN_BINDINGS(skia) {
    class_<SkPath>("SkPath")
        .constructor<>()

        // Path2D API
        .function("addPath",
            select_overload<void(SkPath&, const SkPath&)>(&Path2DAddPath))
        .function("addPath",
            select_overload<void(SkPath&, const SkPath&, emscripten::val)>(&Path2DAddPath))
        .function("arc",
            select_overload<void(SkPath&, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar)>(&Path2DAddArc))
        .function("arc",
            select_overload<void(SkPath&, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar, bool)>(&Path2DAddArc))
        .function("arcTo",
            select_overload<void(SkScalar, SkScalar, SkScalar, SkScalar, SkScalar)>(&SkPath::arcTo))
        .function("bezierCurveTo",
            select_overload<void(SkScalar, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar)>(&SkPath::cubicTo))
        .function("closePath", &SkPath::close)
        .function("ellipse",
            select_overload<void(SkPath&, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar)>(&Path2DAddEllipse))
        .function("ellipse",
            select_overload<void(SkPath&, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar, bool)>(&Path2DAddEllipse))
        .function("lineTo",
            select_overload<void(SkScalar, SkScalar)>(&SkPath::lineTo))
        .function("moveTo",
            select_overload<void(SkScalar, SkScalar)>(&SkPath::moveTo))
        .function("quadraticCurveTo",
            select_overload<void(SkScalar, SkScalar, SkScalar, SkScalar)>(&SkPath::quadTo))
        .function("rect", &Path2DAddRect)

        // Some shorthand helpers, to mirror SkPath.cpp's API
        .function("addPath",
            select_overload<void(SkPath&, const SkPath&, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar)>(&Path2DAddPath))
        .function("addPath",
            select_overload<void(SkPath&, const SkPath&, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar)>(&Path2DAddPath))
        .function("close", &SkPath::close)
        .function("cubicTo",
            select_overload<void(SkScalar, SkScalar, SkScalar, SkScalar, SkScalar, SkScalar)>(&SkPath::cubicTo))
        .function("quadTo",
            select_overload<void(SkScalar, SkScalar, SkScalar, SkScalar)>(&SkPath::quadTo))

        // Extra features
        .function("setFillType", &SkPath::setFillType)
        .function("getFillType", &SkPath::getFillType)
        .function("getBounds", &SkPath::getBounds)
        .function("computeTightBounds", &SkPath::computeTightBounds)

        // PathOps
        .function("simplify", &SimplifyPath)
        .function("op", &ApplyPathOp)

        // Exporting
        .function("toCmds", &ToCmds)
        .function("toPath2D", &ToPath2D)
        .function("toCanvas", &ToCanvas)
        .function("toSVGString", &ToSVGString)

#ifdef PATHKIT_TESTING
        .function("dump", select_overload<void() const>(&SkPath::dump))
#endif
        ;

    class_<SkOpBuilder>("SkOpBuilder")
        .constructor<>()

        .function("add", &SkOpBuilder::add)
        .function("resolve", &ResolveBuilder);

    // Without these function() bindings, the function would be exposed but oblivious to
    // our types (e.g. SkPath)

    // Import
    function("FromSVGString", &FromSVGString);
    function("FromCmds", &FromCmds);
    function("NewPath", &NewPath);
    // Path2D is opaque, so we can't read in from it.

    // PathOps
    function("ApplyPathOp", &ApplyPathOp);

    enum_<SkPathOp>("PathOp")
        .value("DIFFERENCE",         SkPathOp::kDifference_SkPathOp)
        .value("INTERSECT",          SkPathOp::kIntersect_SkPathOp)
        .value("UNION",              SkPathOp::kUnion_SkPathOp)
        .value("XOR",                SkPathOp::kXOR_SkPathOp)
        .value("REVERSE_DIFFERENCE", SkPathOp::kReverseDifference_SkPathOp);

    enum_<SkPath::FillType>("FillType")
        .value("WINDING",            SkPath::FillType::kWinding_FillType)
        .value("EVENODD",            SkPath::FillType::kEvenOdd_FillType)
        .value("INVERSE_WINDING",    SkPath::FillType::kInverseWinding_FillType)
        .value("INVERSE_EVENODD",    SkPath::FillType::kInverseEvenOdd_FillType);

    constant("MOVE_VERB",  MOVE);
    constant("LINE_VERB",  LINE);
    constant("QUAD_VERB",  QUAD);
    constant("CUBIC_VERB", CUBIC);
    constant("CLOSE_VERB", CLOSE);

    // A value object is much simpler than a class - it is returned as a JS
    // object and does not require delete().
    // https://kripken.github.io/emscripten-site/docs/porting/connecting_cpp_and_javascript/embind.html#value-types
    value_object<SkRect>("SkRect")
        .field("fLeft",   &SkRect::fLeft)
        .field("fTop",    &SkRect::fTop)
        .field("fRight",  &SkRect::fRight)
        .field("fBottom", &SkRect::fBottom);

    function("MakeLTRBRect", &SkRect::MakeLTRB);

    // coming soon - Stroke

    // coming soon - Matrix

    // coming soon - Trim

    // Test Utils
    function("SkBits2FloatUnsigned", &SkBits2FloatUnsigned);
}