Windows下从源码编译Skia一文介绍了Skia的编译，现在我们可以尝试在PPAPI插件中来使用Skia了。

Skia的关键类库

官网https://skia.org/上有文档，可以看。然后下载的源码，可以使用SourceInsight之类的工具来查看。具体不再细说，我这里只提用到的三个关键类：

SkCanvas是画布，你可以在它上面画任意的图元，比如矩形、圆型、文字、弧……

SkPaint则是工具箱，聚合了画笔、颜色等各种绘画时要用的配置选项。

SkBitmap代表了一块图像数据。

你调用SkCanvas的方法绘制图元，这些图元对应的数据一定要有个地方保存或显示，用于保存或显示图像数据的那个角色，被称为backends。SkCanvas的backends，有好几种，我们这个简单的示例ppapi_skia只用到了SkBitmap这种后端。

2D绘图类库的基本设计都差不多，我的《Qt on Android核心编程》一书里对Qt绘图有介绍，两厢比对，就会发现设计得差不多。不过有一点不同，QPainter会保存你设置的绘图选项（颜色、画笔等），而SkCanvas则不会，需要自己设计数据结构和逻辑来保存。

ppapi_skia项目

ppapi_skia项目基于ppapi_simple而来，请先参考PPAPI插件的绘图与输入事件处理这篇文章。

不过为了方便调用Skia（C++类库），我这次用了cpp源文件，ppapi_skia.cpp。（吐槽下，VS2013对于C文件的即时提示太弱……）

我还改了ppapi_simple，使用了FlushCompletionCallback来优化绘图流程。

Skia默认编译出来的是静态库，对于一个简单的PPAPI+Skia插件，我不知道需要链接哪些lib，写好了代码，编译，根据undefined reference错误一通狂找，发现要链接下列lib：

skia_core.lib
skia_ports.lib
skia_utils.lib
skia_effects.lib
skia_skgpu.lib
skia_opts.lib
skia_opts_ssse3.lib
skia_opts_sse41.lib
skia_opts_avx.lib
skia_images.lib
skia_sfnt.lib
libetc1.lib
libSkKTX.lib
opengl32.lib

Windows下从源码编译Skia一文提到编译后的lib文件路径是：E:\sources\skia\out\Release。设置到项目的附加库目录列表中。skia还依赖其他一些库文件，在E:\sources\skia\out\Release\obj\gyp目录下，把这个目录添加到附加库目录列表里。

Skia需要OpenGL，我们得链接Opengl32.lib，Windows SDK里有。

skia编译时加了/MD参数，CEF编译时用的MT，如果你用PPAPI的C++接口，就会冲突了。要么改skia，要么改CEF。skia库小，改它吧。我还没找到怎么在生成构建文件时设置，最简单直接的，就是到E:\sources\skia\out\Release\obj\gyp这里，把*.ninja文件里的/MD都修改为/MT。然后重新编译。

如过用C接口，没关系，把PPAPI的代码生成选项里的运行库修改为MD即可。我偷懒，就用C接口，把ppapi_skia项目的运行库选项设置为了MD。

好，关于工程基本就这样了。

源码

分C++源码和HTML源码。

C++代码

So，源码来了，基于C代码改过来，有点乱，不过可以说明用法。

/*
* Copyright (c) 2016 foruok@程序视界. All rights reserved.
* 2016-1-16, edited by foruok.
* 如需转载，请关注微信订阅号“程序视界”，回复foruok获取其联系方式
*/
#include 
#include 
#include 
#include 
#include 

#include "ppapi/c/pp_completion_callback.h"
#include "ppapi/c/pp_errors.h"
#include "ppapi/c/pp_instance.h"
#include "ppapi/c/pp_module.h"
#include "ppapi/c/pp_rect.h"
#include "ppapi/c/pp_var.h"
#include "ppapi/c/ppb.h"
#include "ppapi/c/ppb_core.h"
#include "ppapi/c/ppb_graphics_2d.h"
#include "ppapi/c/ppb_image_data.h"
#include "ppapi/c/ppb_instance.h"
#include "ppapi/c/ppb_view.h"
#include "ppapi/c/ppp.h"
#include "ppapi/c/ppp_instance.h"
#include "ppapi/c/ppb_input_event.h"
#include "ppapi/c/ppp_input_event.h"
#include "SkPaint.h"
#include "SkBitmap.h"
#include "SkCanvas.h"

PPB_GetInterface g_get_browser_interface = NULL;

const PPB_Core* g_core_interface;
const PPB_Graphics2D* g_graphics_2d_interface;
const PPB_ImageData* g_image_data_interface;
const PPB_Instance* g_instance_interface;
const PPB_View* g_view_interface;
const PPB_InputEvent *g_input_interface;
const PPB_MouseInputEvent *g_mouse_interface;

/* PPP_Instance implementation -----------------------------------------------*/

struct InstanceInfo {
    PP_Instance pp_instance;
    struct PP_Size last_size;
    PP_Resource graphics;
    PP_Resource image;
    SkBitmap *bitmap;
    SkCanvas *canvas;
    int inFlush;
    int requestPaint;
    unsigned int colorIndex;

    struct InstanceInfo* next;
};

/** Linked list of all live instances. */
struct InstanceInfo* all_instances = NULL;

/** Returns a refed resource corresponding to the created graphics 2d. */
PP_Resource MakeAndBindGraphics2D(PP_Instance instance,
    const struct PP_Size* size) {
    PP_Resource graphics;

    graphics = g_graphics_2d_interface->Create(instance, size, PP_FALSE);
    if (!graphics)
        return 0;

    if (!g_instance_interface->BindGraphics(instance, graphics)) {
        g_core_interface->ReleaseResource(graphics);
        return 0;
    }
    return graphics;
}

unsigned int g_colors[4] = { 0xFF0000FF, 0xFFFF00FF, 0xFF00FFFF, 0xFFEA00FF };

void DoPaint(struct InstanceInfo * instance);

void FlushCompletionCallback(void* user_data, int32_t result) {
    struct InstanceInfo *inst = (struct InstanceInfo*)user_data;
    inst->inFlush = 0;
    if (inst->requestPaint)
    {
        inst->requestPaint = 0;
        DoPaint(inst);
    }
}

const char szHelloSkia[] = "Hello Skia in PPAPI";
void DoPaint(struct InstanceInfo * instance)
{
    instance->inFlush = 1;
    instance->colorIndex++;
    if (instance->colorIndex >= sizeof(g_colors) / sizeof(g_colors[0])) instance->colorIndex = 0;

    /* [2] Skia Paint * foruok */
    instance->canvas->drawColor(g_colors[instance->colorIndex]);
    SkPaint paint;
    paint.setColor(SK_ColorWHITE);
    paint.setAntiAlias(true);
    paint.setLCDRenderText(true);
    paint.setStrokeWidth(4);

    instance->canvas->drawText(szHelloSkia, ARRAYSIZE(szHelloSkia) - 1, 20.0f, 20.0f, paint);
    paint.setColor(0x80CCCCCC);
    instance->canvas->drawCircle(150, 130, 100, paint);

    /* Paint image to graphics 2d. */
    g_graphics_2d_interface->ReplaceContents(instance->graphics, instance->image);
    g_graphics_2d_interface->Flush(instance->graphics,
        PP_MakeCompletionCallback(&FlushCompletionCallback, instance));
}

void Repaint(struct InstanceInfo* instance, const struct PP_Size* size) {
    /* Ensure the graphics 2d is ready. */
    if (!instance->graphics) {
        instance->graphics = MakeAndBindGraphics2D(instance->pp_instance, size);
        if (!instance->graphics)
            return;
    }

    /* Create image data to paint into. */
    if (!instance->image)
    {
        instance->image = g_image_data_interface->Create(
            instance->pp_instance, PP_IMAGEDATAFORMAT_BGRA_PREMUL, size, PP_TRUE);
        if (!instance->image)
            return;
    }

    /* [1] setup SkCanvas's backends * foruok */
    if (!instance->bitmap)
    {
        /* foruok * get image data from PPB interfaces */
        struct PP_ImageDataDesc image_desc;
        uint32_t* image_data;
        g_image_data_interface->Describe(instance->image, &image_desc);
        image_data = (uint32_t*)g_image_data_interface->Map(instance->image);
        if (!image_data) {
            g_core_interface->ReleaseResource(instance->image);
            return;
        }

        /* foruok * bind PPAPI image data to SkBitmap */
        SkImageInfo ii = SkImageInfo::Make(size->width, size->height, 
            kBGRA_8888_SkColorType, kPremul_SkAlphaType, 
            kLinear_SkColorProfileType);
        instance->bitmap = new SkBitmap();
        instance->bitmap->installPixels(ii, image_data, image_desc.stride);

        if (!instance->canvas)
        {
            /* foruok * construct SkCanvas with SkBitmap backend */
            instance->canvas = new SkCanvas(*instance->bitmap);
        }
    }

    if (!instance->inFlush)
    {
        DoPaint(instance);
    }
    else
    {
        instance->requestPaint = 1;
    }
}

/** Returns the info for the given instance, or NULL if it's not found. */
struct InstanceInfo* FindInstance(PP_Instance instance) {
    struct InstanceInfo* cur = all_instances;
    while (cur) {
        if (cur->pp_instance == instance)
            return cur;
        cur = cur->next;
    }
    return NULL;
}

PP_Bool Instance_DidCreate(PP_Instance instance,
    uint32_t argc,
    const char* argn[],
    const char* argv[]) {
    struct InstanceInfo* info =
        (struct InstanceInfo*)calloc(1, sizeof(struct InstanceInfo));
    info->pp_instance = instance;

    /* Insert into linked list of live instances. */
    info->next = all_instances;
    all_instances = info;

    g_input_interface->RequestInputEvents(instance, PP_INPUTEVENT_CLASS_MOUSE);
    g_input_interface->RequestFilteringInputEvents(instance, PP_INPUTEVENT_CLASS_MOUSE);
    OutputDebugString(_T("Instance_DidCreate\r\n"));

    return PP_TRUE;
}

void Instance_DidDestroy(PP_Instance instance) {
    /* Find the matching item in the linked list, delete it, and patch the
    * links.
    */
    struct InstanceInfo** prev_ptr = &all_instances;
    struct InstanceInfo* cur = all_instances;
    while (cur) {
        if (instance == cur->pp_instance) {
            *prev_ptr = cur->next;
            g_core_interface->ReleaseResource(cur->graphics);
            free(cur);
            return;
        }
        prev_ptr = &cur->next;
        cur = cur->next;
    }
}

void Instance_DidChangeView(PP_Instance pp_instance,
    PP_Resource view) {
    struct PP_Rect position;
    struct InstanceInfo* info = FindInstance(pp_instance);
    if (!info)
        return;

    if (g_view_interface->GetRect(view, &position) == PP_FALSE)
        return;

    if (info->last_size.width != position.size.width ||
        info->last_size.height != position.size.height) {
        /* Got a resize, repaint the plugin. */
        Repaint(info, &position.size);
        info->last_size.width = position.size.width;
        info->last_size.height = position.size.height;
    }

    OutputDebugString(_T("Instance_DidChangeView\r\n"));
}

void Instance_DidChangeFocus(PP_Instance pp_instance, PP_Bool has_focus) {
}

PP_Bool Instance_HandleDocumentLoad(PP_Instance pp_instance,
    PP_Resource pp_url_loader) {
    return PP_FALSE;
}

static PPP_Instance instance_interface = {
    &Instance_DidCreate,
    &Instance_DidDestroy,
    &Instance_DidChangeView,
    &Instance_DidChangeFocus,
    &Instance_HandleDocumentLoad
};

PP_Bool InputEvent_HandleInputEvent(PP_Instance instance, PP_Resource input_event)
{
    struct PP_Point pt;
    TCHAR szLog[512] = { 0 };
    switch (g_input_interface->GetType(input_event))
    {
    case PP_INPUTEVENT_TYPE_MOUSEDOWN:
        pt = g_mouse_interface->GetPosition(input_event);
        _stprintf_s(szLog, 512, _T("InputEvent_HandleInputEvent, mouse down at [%d, %d]\r\n"), pt.x, pt.y);
        OutputDebugString(szLog);
        break;
        /*
    case PP_INPUTEVENT_TYPE_MOUSEUP:
        OutputDebugString(_T("InputEvent_HandleInputEvent, mouse up\r\n"));
        break;

    case PP_INPUTEVENT_TYPE_MOUSEMOVE:
        OutputDebugString(_T("InputEvent_HandleInputEvent, mouse move\r\n"));
        break;
    case PP_INPUTEVENT_TYPE_MOUSEENTER:
        OutputDebugString(_T("InputEvent_HandleInputEvent, mouse enter\r\n"));
        break;
    case PP_INPUTEVENT_TYPE_MOUSELEAVE:
        OutputDebugString(_T("InputEvent_HandleInputEvent, mouse leave\r\n"));
        break;
        */
    default:
        return PP_FALSE;
    }
    struct InstanceInfo* info = FindInstance(instance);
    if (info && info->last_size.width > 0)
    {
        Repaint(info, &info->last_size);
    }
    return PP_TRUE;
}

static PPP_InputEvent input_interface = {
    &InputEvent_HandleInputEvent
};

/* Global entrypoints --------------------------------------------------------*/

PP_EXPORT int32_t PPP_InitializeModule(PP_Module module,
    PPB_GetInterface get_browser_interface) {
    g_get_browser_interface = get_browser_interface;

    g_core_interface = (const PPB_Core*)
        get_browser_interface(PPB_CORE_INTERFACE);
    g_instance_interface = (const PPB_Instance*)
        get_browser_interface(PPB_INSTANCE_INTERFACE);
    g_image_data_interface = (const PPB_ImageData*)
        get_browser_interface(PPB_IMAGEDATA_INTERFACE);
    g_graphics_2d_interface = (const PPB_Graphics2D*)
        get_browser_interface(PPB_GRAPHICS_2D_INTERFACE);
    g_view_interface = (const PPB_View*)
        get_browser_interface(PPB_VIEW_INTERFACE);
    g_input_interface = (const PPB_InputEvent*)get_browser_interface(PPB_INPUT_EVENT_INTERFACE);
    g_mouse_interface = (const PPB_MouseInputEvent*)get_browser_interface(PPB_MOUSE_INPUT_EVENT_INTERFACE);

    if (!g_core_interface || !g_instance_interface || !g_image_data_interface ||
        !g_graphics_2d_interface || !g_view_interface ||
        !g_input_interface || !g_mouse_interface)
        return -1;

    OutputDebugString(_T("PPP_InitializeModule\r\n"));
    return PP_OK;
}

PP_EXPORT void PPP_ShutdownModule() {
}

PP_EXPORT const void* PPP_GetInterface(const char* interface_name) {
    if (strcmp(interface_name, PPP_INSTANCE_INTERFACE) == 0)
    {
        OutputDebugString(_T("PPP_GetInterface, instance_interface\r\n"));
        return &instance_interface;
    }
    else if (strcmp(interface_name, PPP_INPUT_EVENT_INTERFACE) == 0)
    {
        OutputDebugString(_T("PPP_GetInterface, input_interface\r\n"));
        return &input_interface;
    }

    return NULL;
}

上面代码里我标注了两处与Skia有关的改动，[1]和[2]，也加了注释。另外就是使用FlushCompletionCallback来处理绘图和刷新，把ppapi_simple中的一些全局变量修改为与插件实例对象绑定的变量，这样可以支持一个网页里嵌入多个plugin了。

HTML代码

ppapi_skia.html代码如下：