experimental/wasm-skp-debugger/debugger_bindings.cpp

/*
 * Copyright 2019 Google LLC
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "SkDebugCanvas.h"
#include "SkPicture.h"
#include "SkSurface.h"
#include <emscripten.h>
#include <emscripten/bind.h>

using JSColor = int32_t;

struct SimpleImageInfo {
  int width;
  int height;
  SkColorType colorType;
  SkAlphaType alphaType;
};

SkImageInfo toSkImageInfo(const SimpleImageInfo& sii) {
  return SkImageInfo::Make(sii.width, sii.height, sii.colorType, sii.alphaType);
}

class SkpDebugPlayer {
  public:
    SkpDebugPlayer() {}


    /* loadSkp deserializes a skp file that has been copied into the shared WASM memory.
     * cptr - a pointer to the data to deserialize.
     * length - length of the data in bytes.
     * The caller must allocate the memory with M._malloc where M is the wasm module in javascript
     * and copy the data into M.buffer at the pointer returned by malloc.
     *
     * uintptr_t is used here because emscripten will not allow binding of functions with pointers
     * to primitive types. We can instead pass a number and cast it to whatever kind of
     * pointer we're expecting.
     */
    void loadSkp(uintptr_t cptr, int length) {
      const auto* data = reinterpret_cast<const uint8_t*>(cptr);
      // todo: pass in bounds
      fDebugCanvas.reset(new SkDebugCanvas(720, 1280));
      SkDebugf("SkDebugCanvas created.\n");
      // note overloaded = operator that actually does a move
      fPicture = SkPicture::MakeFromData(data, length);
      if (!fPicture) {
        SkDebugf("Unable to parse SKP file.\n");
        return;
      }
      SkDebugf("Parsed SKP file.\n");
      // Only draw picture to the debug canvas once.
      fDebugCanvas->drawPicture(fPicture);
      SkDebugf("Added picture with %d commands.\n", fDebugCanvas->getSize());
    }

    /* drawTo asks the debug canvas to draw from the beginning of the picture
     * to the given command and flush the canvas.
     */
    void drawTo(SkSurface* surface, int32_t index) {
      fDebugCanvas->drawTo(surface->getCanvas(), index);
      surface->getCanvas()->flush();
    }

  private:
    // admission of ignorance - don't know when to use unique pointer or sk_sp
    std::unique_ptr<SkDebugCanvas> fDebugCanvas;
    sk_sp<SkPicture> fPicture;
};

using namespace emscripten;
EMSCRIPTEN_BINDINGS(my_module) {

  // The main class that the JavaScript in index.html uses
  class_<SkpDebugPlayer>("SkpDebugPlayer")
    .constructor<>()
    .function("loadSkp", &SkpDebugPlayer::loadSkp, allow_raw_pointers())
    .function("drawTo", &SkpDebugPlayer::drawTo, allow_raw_pointers());

  // Symbols needed by cpu.js to perform surface creation and flushing.
  enum_<SkColorType>("ColorType")
    .value("RGBA_8888", SkColorType::kRGBA_8888_SkColorType);
  enum_<SkAlphaType>("AlphaType")
    .value("Unpremul", SkAlphaType::kUnpremul_SkAlphaType);
  value_object<SimpleImageInfo>("SkImageInfo")
    .field("width",     &SimpleImageInfo::width)
    .field("height",    &SimpleImageInfo::height)
    .field("colorType", &SimpleImageInfo::colorType)
    .field("alphaType", &SimpleImageInfo::alphaType);
  constant("TRANSPARENT", (JSColor) SK_ColorTRANSPARENT);
  function("_getRasterDirectSurface", optional_override([](const SimpleImageInfo ii,
                                                           uintptr_t /* uint8_t*  */ pPtr,
                                                           size_t rowBytes)->sk_sp<SkSurface> {
    uint8_t* pixels = reinterpret_cast<uint8_t*>(pPtr);
    SkImageInfo imageInfo = toSkImageInfo(ii);
    return SkSurface::MakeRasterDirect(imageInfo, pixels, rowBytes, nullptr);
  }), allow_raw_pointers());
  class_<SkSurface>("SkSurface")
    .smart_ptr<sk_sp<SkSurface>>("sk_sp<SkSurface>")
    .function("width", &SkSurface::width)
    .function("height", &SkSurface::height)
    .function("_flush", select_overload<void()>(&SkSurface::flush))
    .function("getCanvas", &SkSurface::getCanvas, allow_raw_pointers());
  class_<SkCanvas>("SkCanvas")
    .function("clear", optional_override([](SkCanvas& self, JSColor color)->void {
      // JS side gives us a signed int instead of an unsigned int for color
      // Add a optional_override to change it out.
      self.clear(SkColor(color));
    }));
}