implement Canvas.

src/canvas.cc

+#include <exception>
 #include "canvas.h"
+#include "pixelTypes.h"
+#include "include/core/SkCanvas.h"
+#include "include/core/SkImageInfo.h"
+#include "include/core/SkColorType.h"
 
-std::shared_ptr<Canvas> Canvas::MakeCanvas(int width, int height, PixelTypes pixType) {
+namespace {
 
+SkColorType pixelTypeConvert(PixelType type) {
+    switch (type) {
+    case RGBA:
+        return kRGBA_8888_SkColorType;
+    default:
+        throw std::runtime_error("invalid pixel type");
+    }
+}
+
+SkAlphaType alphaTypeConvert(AlphaType alpha) {
+    switch (alpha) {
+    case PREMUL:
+        return kPremul_SkAlphaType;
+    default:
+        throw std::runtime_error("invalid alpha type");
+    }
+}
+
+};
+
+std::unique_ptr<Canvas> Canvas::MakeCanvas(
+    int width, int height, PixelType pixType, AlphaType alpha) {
+    std::unique_ptr<Canvas> canvas =
+        std::make_unique<Canvas>(width, height, pixType);
+    return canvas;
+}
+
+Canvas::Canvas(int width, int height, PixelType pixType, AlphaType alpha): canvas_(nullptr) {
+    SkImageInfo imgInfo = SkImageInfo::Make(
+        width, height,
+        pixelTypeConvert(pixType),
+        alphaTypeConvert(alpha));
+    uint8_t *buffer = new uint8_t[width * height * 4];
+
+    canvas_ = SkCanvas::MakeRasterDirect(imgInfo, buffer, width * 4);
 }

src/canvas.h

 
 #include <memory>
+#include "pixelTypes.h"
+#include "include/core/SkCanvas.h"
 #include "Drawable.h"
 
 #ifndef CANVAS_H
 #define CANVAS_H
 
-enum PixelTypes {};
-
 class Canvas {
 public:
-    static std::shared_ptr<Canvas> MakeCanvas(int width, int height, PixelTypes pixType);
+    static std::unique_ptr<Canvas> MakeCanvas(
+        int width, int height, PixelType pixType, AlphaType alpha);
 
     template<typename T>
     bool draw(Drawable<T>* drawable);
 
 protected:
-    Canvas(int width, int height, PixelTypes pixType);
+    Canvas(int width, int height, PixelType pixType, AlphaType alpha);
+private:
+    std::unique_ptr<SkCanvas> canvas_;
 };
 
 #endif /* CANVAS_H */

src/pixelTypes.h

+
+#ifndef PIXELTYPES_H
+#define PIXELTYPES_H
+
+enum PixelType {
+    RGBA = 0,
+};
+
+enum AlphaType {
+    PREMUL,
+};
+
+#endif /* PIXELTYPES_H */