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接这篇文章（附完整工程代码地址）

原理示意图：

首选检查显卡是否支持 PBO :

#if defined(_WIN32)    // check PBO is supported by your video card	// 检查显卡是否支持 PBO    if (glInfo.isExtensionSupported("GL_ARB_pixel_buffer_object"))    {        // get pointers to GL functions        glGenBuffersARB = (PFNGLGENBUFFERSARBPROC)wglGetProcAddress("glGenBuffersARB");        glBindBufferARB = (PFNGLBINDBUFFERARBPROC)wglGetProcAddress("glBindBufferARB");        glBufferDataARB = (PFNGLBUFFERDATAARBPROC)wglGetProcAddress("glBufferDataARB");        glBufferSubDataARB = (PFNGLBUFFERSUBDATAARBPROC)wglGetProcAddress("glBufferSubDataARB");        glDeleteBuffersARB = (PFNGLDELETEBUFFERSARBPROC)wglGetProcAddress("glDeleteBuffersARB");        glGetBufferParameterivARB = (PFNGLGETBUFFERPARAMETERIVARBPROC)wglGetProcAddress("glGetBufferParameterivARB");        glMapBufferARB = (PFNGLMAPBUFFERARBPROC)wglGetProcAddress("glMapBufferARB");        glUnmapBufferARB = (PFNGLUNMAPBUFFERARBPROC)wglGetProcAddress("glUnmapBufferARB");        // check once again PBO extension        if (glGenBuffersARB && glBindBufferARB && glBufferDataARB && glBufferSubDataARB &&                glMapBufferARB && glUnmapBufferARB && glDeleteBuffersARB && glGetBufferParameterivARB)        {            pboSupported = true;            pboMode = 1;    // using 1 PBO            cout << "Video card supports GL_ARB_pixel_buffer_object." << endl;        }        else        {            pboSupported = false;            pboMode = 0;    // without PBO            cout << "Video card does NOT support GL_ARB_pixel_buffer_object." << endl;        }    }    // Query the system memory page size and update the default value    SYSTEM_INFO si;    GetSystemInfo(&si);    if (si.dwPageSize > 0)    {        systemPageSize = si.dwPageSize;    }#elif defined (__gnu_linux__)    // for linux, do not need to get function pointers, it is up-to-date    if (glInfo.isExtensionSupported("GL_ARB_pixel_buffer_object"))    {        pboSupported = true;        cout << "Video card supports GL_ARB_pixel_buffer_object" << endl;    }    else    {        cout << "Video card does NOT support GL_ARB_pixel_buffer_object" << endl;    }    if (glInfo.isExtensionSupported("GL_AMD_pinned_memory"))    {        amdSupported = true;        cout << "Video card supports GL_AMD_pinned_memory" << endl;    }    else    {        cout << "Video card does NOT support GL_AMD_pinned_memory" << endl;    }    // Query the system memory page size and update the default value    if (sysconf(_SC_PAGE_SIZE) > 0)    {        systemPageSize = sysconf(_SC_PAGE_SIZE);    }#endif

// 创建 count 个 PBOvoid setPboCount(int count){    if (!pboSupported)        return;	// 如果 count 大于 当前的 PBO 数    if (count > pboCount)    {        if (pboMethod != AMD)        {            // Generate each Pixel Buffer object and allocate memory for it（生成 PBO，并为其分配内存）            // Hopefully, PBOs will get allocated in VRAM            glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0); // Unbind any buffer object previously bound（释放之前所绑定的 PBO）            for (int i = pboCount; i < count; ++i)            {                GLuint pboId;                glGenBuffers(1, &pboId); // Generate new Buffer Object ID                glBindBuffer(GL_PIXEL_UNPACK_BUFFER, pboId); // Create a zero-sized memory Pixel Buffer Object and bind it                glBufferData(GL_PIXEL_UNPACK_BUFFER, DATA_SIZE, NULL, GL_STREAM_DRAW); // Reserve the memory space for the PBO                glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0); // Release the PBO binding                pboIds.push_back(pboId); // Update our list of PBO IDs                pboFences.push_back(NULL);                cout << "Created PBO buffer #" << i << " of size: " << DATA_SIZE << endl;            }            pboCount = pboIds.size();            assert(GL_NO_ERROR == glGetError());        }		// 特殊的 DMA 模式，需要自己手动分配对齐的内存，并提供内存指针        else        {            // Generate each Pixel Buffer object and allocate memory for it            // PBOs will get allocated in System RAM, and GPU will access it through DMA            glBindBuffer(GL_EXTERNAL_VIRTUAL_MEMORY_BUFFER_AMD, 0); // Unbind any buffer object previously bound            for (int i = pboCount; i < count; ++i)            {                GLuint pboId;                glGenBuffers(1, &pboId); // Generate new Buffer Object ID                glBindBuffer(GL_EXTERNAL_VIRTUAL_MEMORY_BUFFER_AMD, pboId); // Create a zero-sized memory Pixel Buffer Object and bind it                assert(GL_NO_ERROR == glGetError());                // Memory alignment functions are compiler-specific                GLubyte *ptAlignedBuffer = (GLubyte *)alignedMalloc(systemPageSize, DATA_SIZE);                if (NULL == ptAlignedBuffer)                {                    cout << "ERROR [setPboCount] (alignedMalloc) size: " << DATA_SIZE << " alignment: " << systemPageSize << endl;                    break;                }                cout << "Created memory buffer #" << i << " of size: " << DATA_SIZE << " alignment: " << systemPageSize << endl;                glBufferData(GL_EXTERNAL_VIRTUAL_MEMORY_BUFFER_AMD, DATA_SIZE, ptAlignedBuffer, GL_STREAM_DRAW); // Take control of the memory space for the PBO                GLenum error = glGetError();                if (GL_NO_ERROR != error)                {                    cout << "ERROR [setPboCount] (glBufferData): " << (char *)gluErrorString(error) << endl;                    alignedFree(ptAlignedBuffer);                    cout << "Freed memory buffer #" << i << endl;                    break;                }                glBindBuffer(GL_EXTERNAL_VIRTUAL_MEMORY_BUFFER_AMD, 0); // Release the PBO binding                assert(GL_NO_ERROR == glGetError());                pboIds.push_back(pboId); // Update our list of PBO IDs                pboFences.push_back(NULL);                alignedBuffers.push_back((GLubyte *)ptAlignedBuffer);                cout << "Created PBO buffer #" << i << endl;            }            pboCount = pboIds.size();            assert(GL_NO_ERROR == glGetError());        }    }	// 如果 count 小于当前的 PBO 数    else if (count < pboCount)    {        if (pboMethod != AMD)        {            glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0); // Unbind any buffer object previously bound            for (int i = pboCount - 1; i >= count; --i)            {                glDeleteSync(pboFences.back());                pboFences.pop_back();                GLuint pboId = pboIds.back();                glDeleteBuffers(1, &pboId);                pboIds.pop_back(); // Update our list of PBO IDs                cout << "Deleted PBO buffer #" << i << endl;            }            pboCount = pboIds.size();            assert(GL_NO_ERROR == glGetError());        }        else        {            glBindBuffer(GL_EXTERNAL_VIRTUAL_MEMORY_BUFFER_AMD, 0); // Unbind any buffer object previously bound            for (int i = pboCount - 1; i >= count; --i)            {                glDeleteSync(pboFences.back());                pboFences.pop_back();                GLuint pboId = pboIds.back();                glDeleteBuffers(1, &pboId);                pboIds.pop_back(); // Update our list of PBO IDs                cout << "Deleted PBO buffer #" << i << endl;				// 手动释放自己分配的内存                alignedFree(alignedBuffers.back());                alignedBuffers.pop_back();                cout << "Freed memory buffer #" << i << endl;            }            pboCount = pboIds.size();            assert(GL_NO_ERROR == glGetError());        }    }    cout << "PBO Count: " << pboCount << endl;}

最关键的显示回调方法：

void displayCB(){    if (pboMethod == NONE)    {        /*        * Update data in System Memory.        */        t1.start();        updatePixels(imageData, DATA_SIZE);	// 更新 imageData 的像素        t1.stop();        updateTime = t1.getElapsedTimeInMilliSec();        /*        * Copy data from System Memory to texture object. （将 imageData 的内容从内存拷贝到纹理当中）        */        t1.start();        glBindTexture(GL_TEXTURE_2D, textureId);        glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, IMAGE_WIDTH, IMAGE_HEIGHT, PIXEL_FORMAT, GL_UNSIGNED_BYTE, (GLvoid *)imageData);        t1.stop();        copyTime = t1.getElapsedTimeInMilliSec();    }    else    {        /*        * Update buffer indices used in data upload & copy.        *        * "uploadIdx": index used to upload pixels to a Pixel Buffer Object.（上传像素至 uploadIdx 指定的 PBO）        * "copyIdx": index used to copy pixels from a Pixel Buffer Object to a GPU texture.（拷贝 cpyIdx 指定的 PBO 的像素到 GPU 纹理）        *        * When (pboCount > 1), this will allow to perform（当 pboCount 数大于1时，就允许使用备用buffer来同时进行上传和拷贝）        * simultaneous upload & copy, by using alternative buffers.        * That is a good thing, unless the double buffering is being already        * done somewhere else in the code.        */        static int copyIdx = 0;        copyIdx = (copyIdx + 1) % pboCount;        int uploadIdx = (copyIdx + 1) % pboCount;        /*        * Upload new data to a Pixel Buffer Object.        */        t1.start();        glBindBuffer(GL_PIXEL_UNPACK_BUFFER, pboIds[uploadIdx]); // Access the Pixel Buffer Object and bind it		// pboMethod 表示不同的纹理流机制（Texture Stream methods）        if (pboMethod == ORPHAN)        {			// GL_STREAM_DRAW 表示每次渲染都会更新该 PBO的像素数据			// GL_DYNAMITC_DRAW 表示每帧都会更新该 Buffer			// GL_STATIC_DRAW 表示几乎或从不更新该 Buffer            glBufferDataARB(GL_PIXEL_UNPACK_BUFFER_ARB, DATA_SIZE, NULL, GL_STREAM_DRAW_ARB);			// 获得 PBO 的映射 Buffer 指针，以待写入操作            GLubyte *ptr = (GLubyte *)glMapBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB, GL_WRITE_ONLY_ARB);            if (NULL == ptr)            {                cout << "ERROR [displayCB] (glMapBufferARB): " << (char *)gluErrorString(glGetError()) << endl;                return;            }            else            {                // update data directly on the mapped buffer（在映射的 Buffer 上直接更新 PBO 的像素数据）                updatePixels(ptr, DATA_SIZE);                // release pointer to mapping buffer（释放映射 Buffer 的指针）                if (!glUnmapBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB))                {                    cout << "ERROR [displayCB] (glUnmapBufferARB): " << (char *)gluErrorString(glGetError()) << endl;                }            }        }		// 异步模式        else if (pboMethod == UNSYNCH_ORPHAN || pboMethod == UNSYNCH_FENCES)        {            if (pboMethod == UNSYNCH_FENCES)            {				// 检查索引的pboFences 是否是同步对象（Sync Object）                if (glIsSync(pboFences[uploadIdx]))                {					// 阻塞并 wait 同步对象，等待被 signal                    GLenum result = glClientWaitSync(pboFences[uploadIdx], 0, GL_TIMEOUT_IGNORED);                    switch (result)                    {                    case GL_ALREADY_SIGNALED:                        // Transfer was already done when trying to use buffer						// （说明此时传输已经完成）                        cout << "DEBUG (glClientWaitSync): ALREADY_SIGNALED (good timing!) uploadIdx: " << uploadIdx << endl;                        break;                    case GL_CONDITION_SATISFIED:                        // This means that we had to wait for the fence to synchronize us after using all the buffers,                        // which implies that the GPU command queue is full and that we are GPU-bound (DMA transfers aren't fast enough).						// （说明我们不得不等待 fence 的同步，即 我们所绑定的 GPU 命令队列已满[DMA传输还不够快]）                        cout << "WARNING (glClientWaitSync): CONDITION_SATISFIED (had to wait for the sync) uploadIdx: " << uploadIdx << endl;                        break;                    case GL_TIMEOUT_EXPIRED:                        cout << "WARNING (glClientWaitSync): TIMEOUT_EXPIRED (DMA transfers are too slow!) uploadIdx: " << uploadIdx << endl;                        break;                    case GL_WAIT_FAILED:                        cout << "ERROR (glClientWaitSync): WAIT_FAILED: " << (char *)gluErrorString(glGetError()) << endl;                        break;                    }					// 删除同步对象                    glDeleteSync(pboFences[uploadIdx]);                    pboFences[uploadIdx] = NULL;                }            }			// 注意和 ORPHAN 的区别            else if (pboMethod == UNSYNCH_ORPHAN)            {				// Buffer 需要重新指定                glBufferData(GL_PIXEL_UNPACK_BUFFER, DATA_SIZE, NULL, GL_STREAM_DRAW); // Buffer re-specification (orphaning)            }			// 获得 PBO 的映射 Buffer 指针，以待写入操作            GLubyte *ptr = (GLubyte *)glMapBufferRange(GL_PIXEL_UNPACK_BUFFER, 0, DATA_SIZE, GL_MAP_WRITE_BIT | GL_MAP_UNSYNCHRONIZED_BIT);            if (NULL == ptr)            {                cout << "ERROR [displayCB] (glMapBufferRange): " << (char *)gluErrorString(glGetError()) << endl;                return;            }            else            {                updatePixels(ptr, DATA_SIZE); // Update data directly on the mapped buffer（直接更新映射 Buffer 的数据）                if (!glUnmapBuffer(GL_PIXEL_UNPACK_BUFFER))                {                    cout << "ERROR [displayCB] (glUnmapBuffer): " << (char *)gluErrorString(glGetError()) << endl;                }            }        }        else if (pboMethod == AMD)        {			// 同样要进行手动同步            if (glIsSync(pboFences[uploadIdx]))            {                GLenum result = glClientWaitSync(pboFences[uploadIdx], 0, GL_TIMEOUT_IGNORED);                switch (result)                {                case GL_ALREADY_SIGNALED:                    // Transfer was already done when trying to use buffer                    //cout << "DEBUG (glClientWaitSync): ALREADY_SIGNALED (good timing!) uploadIdx: " << uploadIdx << endl;                    break;                case GL_CONDITION_SATISFIED:                    // This means that we had to wait for the fence to synchronize us after using all the buffers,                    // which implies that the GPU command queue is full and that we are GPU-bound (DMA transfers aren't fast enough).                    //cout << "WARNING (glClientWaitSync): CONDITION_SATISFIED (had to wait for the sync) uploadIdx: " << uploadIdx << endl;                    break;                case GL_TIMEOUT_EXPIRED:                    cout << "WARNING (glClientWaitSync): TIMEOUT_EXPIRED (DMA transfers are too slow!) uploadIdx: " << uploadIdx << endl;                    break;                case GL_WAIT_FAILED:                    cout << "ERROR (glClientWaitSync): WAIT_FAILED: " << (char *)gluErrorString(glGetError()) << endl;                    break;                }                glDeleteSync(pboFences[uploadIdx]);                pboFences[uploadIdx] = NULL;            }			// alignedBuffers 存储的是手动分配的一块对齐过的内存指针            updatePixels(alignedBuffers[uploadIdx], DATA_SIZE); // Update data directly on the mapped buffer        }        t1.stop();        updateTime = t1.getElapsedTimeInMilliSec();        /*        * Protect each Pixel Buffer Object against being overwritten.（防止 PBO 被重复写入）        *        * Tipically the data upload will be slower than our main loop, so this        * function will be called again before the previous frame was uploaded        * and processed. The main bottleneck is the PCI bus transfer speed,        * which limits how fast the DMA (System Memory --> VRAM) can work.		*         * 通常数据上传将会慢于主循环，意味着在先前的帧被上传处理之前，该方法将会被再次调用。		* 主要的性能瓶颈在于 PCI 总线的传输速度， 它限制了 DMA 的传输速度（内存到显存）。		*        * OpenGL Sync Fences will block until the PBO is released.（GL 同步对象将会阻塞主线程，直到 PBO 被释放为止）        */        if (pboMethod == UNSYNCH_FENCES || pboMethod == AMD)        {			// 创建一个同步对象，并将其加入 GL 的命令流中（❤ 具体请参看第八版红宝书的 P589 第11章 Memory ❤）            pboFences[uploadIdx] = glFenceSync(GL_SYNC_GPU_COMMANDS_COMPLETE, 0);        }        /*        * Copy data from a Pixel Buffer Object to a GPU texture.        * glTexSubImage2D() will copy pixels to the corresponding texture in the GPU.		* 传输 PBO 中的数据到 GPU 纹理        */        t1.start();        glBindTexture(GL_TEXTURE_2D, textureId); // Bind the texture        glBindBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB, pboIds[copyIdx]); // Access the Pixel Buffer Object and bind it        // Use offset instead of pointer（由于使用了 PBO，所以传递的是偏移量）        glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, IMAGE_WIDTH, IMAGE_HEIGHT, PIXEL_FORMAT, GL_UNSIGNED_BYTE, 0);        t1.stop();        copyTime = t1.getElapsedTimeInMilliSec();        // it is good idea to release PBOs with ID 0 after use.        // Once bound with 0, all pixel operations behave normal ways.        glBindBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB, 0);    }    // clear buffer    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);    // save the initial ModelView matrix before modifying ModelView matrix    glPushMatrix();    // tramsform camera    glTranslatef(0, 0, -cameraDistance);    glRotatef(cameraAngleX, 1, 0, 0); // pitch    glRotatef(cameraAngleY, 0, 1, 0); // heading    // draw a point with texture    glBindTexture(GL_TEXTURE_2D, textureId);    glColor4f(1, 1, 1, 1);    glBegin(GL_QUADS);    glNormal3f(0, 0, 1);    glTexCoord2f(0.0f, 0.0f);    glVertex3f(-1.0f, -1.0f, 0.0f);    glTexCoord2f(1.0f, 0.0f);    glVertex3f(1.0f, -1.0f, 0.0f);    glTexCoord2f(1.0f, 1.0f);    glVertex3f(1.0f, 1.0f, 0.0f);    glTexCoord2f(0.0f, 1.0f);    glVertex3f(-1.0f, 1.0f, 0.0f);    glEnd();    // unbind texture    glBindTexture(GL_TEXTURE_2D, 0);    // draw info messages    showInfo();    //showTransferRate();    printTransferRate();    glPopMatrix();    glutSwapBuffers();}

运行结果对比：

【未使用 PBO 的情况】

【Orphaning模式，PBO 个数 = 1】

【异步 Orphaning模式， PBO个数 = 1】

【Fences 的 同步模式， PBO个数 = 1】

【Orphaning模式， PBO个数=3】

【异步的 Orphaning 模式， PBO个数=3】

可见使用了 PBO 的确比未使用 PBO 性能要略优，但一味增加 PBO 的数量，并不能显著提高性能。

本例中 不同的 PBO 模式性能差别不大，但是 Orphan 模式的写法最简单，不需要自己手动同步和创建额外对齐的内存。

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