《OpenGL 超级宝典（Super Bible）第五版》 有关 PBO 的 Example

代码即关键注释如下：
static GLfloat vGreen[] = { 0.0f, 1.0f, 0.0f, 1.0f };
static GLfloat vWhite[] = { 1.0f, 1.0f, 1.0f, 1.0f };
static GLfloat vLightPos[] = { 0.0f, 3.0f, 0.0f, 1.0f };

GLsizei screenWidth; // Desired window or desktop width
GLsizei screenHeight; // Desired window or desktop height

GLboolean bFullScreen; // Request to run full screen
GLboolean bAnimated; // Request for continual updates

GLShaderManager shaderManager; // Shader Manager
GLMatrixStack modelViewMatrix; // Modelview Matrix
GLMatrixStack projectionMatrix; // Projection Matrix
M3DMatrix44f orthoMatrix;
GLFrustum viewFrustum; // View Frustum
GLGeometryTransform transformPipeline; // Geometry Transform Pipeline
GLFrame cameraFrame; // Camera frame

GLTriangleBatch torusBatch;
GLBatch floorBatch;
GLBatch screenQuad;

GLuint textures[1];
GLuint blurTextures[6];
GLuint pixBuffObjs[1];
GLuint curBlurTarget;
bool bUsePBOPath;
GLfloat speedFactor;
GLuint blurProg;
void *pixelData;
GLuint pixelDataSize;

//void MoveCamera(void);
void DrawWorld(GLfloat yRot, GLfloat xPos);
bool LoadBMPTexture(const char *szFileName, GLenum minFilter, GLenum magFilter, GLenum wrapMode);

void SetupBlurProg(void);

// returns 1 - 6 for blur texture units
// curPixBuf is always between 0 and 5
void AdvanceBlurTaget()
{
curBlurTarget = ((curBlurTarget + 1) % 6);
}
GLuint GetBlurTarget0()
{
return (1 + ((curBlurTarget + 5) % 6));
}
GLuint GetBlurTarget1()
{
return (1 + ((curBlurTarget + 4) % 6));
}
GLuint GetBlurTarget2()
{
return (1 + ((curBlurTarget + 3) % 6));
}
GLuint GetBlurTarget3()
{
return (1 + ((curBlurTarget + 2) % 6));
}
GLuint GetBlurTarget4()
{
return (1 + ((curBlurTarget + 1) % 6));
}
GLuint GetBlurTarget5()
{
return (1 + ((curBlurTarget) % 6));
}

void UpdateFrameCount()
{
static int iFrames = 0; // Frame count
static CStopWatch frameTimer; // Render time

// Reset the stopwatch on first time
if(iFrames == 0)
{
frameTimer.Reset();
iFrames++;
}
// Increment the frame count
iFrames++;

// Do periodic frame rate calculation
if (iFrames == 101)
{
float fps;

fps = 100.0f / frameTimer.GetElapsedSeconds();
if (bUsePBOPath)
printf("Pix_buffs - Using PBOs %.1f fps\n", fps);
else
printf("Pix_buffs - Using Client mem copies %.1f fps\n", fps);

frameTimer.Reset();
iFrames = 1;
}
}

///////////////////////////////////////////////////////////////////////////////////////////////////////
// Load in a BMP file as a texture. Allows specification of the filters and the wrap mode
bool LoadBMPTexture(const char *szFileName, GLenum minFilter, GLenum magFilter, GLenum wrapMode)
{
GLbyte *pBits;
GLint iWidth, iHeight;

pBits = gltReadBMPBits(szFileName, &iWidth, &iHeight);
if(pBits == NULL)
return false;

// Set Wrap modes
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, wrapMode);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, wrapMode);

// Do I need to generate mipmaps?
if(minFilter == GL_LINEAR_MIPMAP_LINEAR || minFilter == GL_LINEAR_MIPMAP_NEAREST || minFilter == GL_NEAREST_MIPMAP_LINEAR || minFilter == GL_NEAREST_MIPMAP_NEAREST)
glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, minFilter);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, magFilter);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, iWidth, iHeight, 0, GL_BGR, GL_UNSIGNED_BYTE, pBits);
return true;
}

///////////////////////////////////////////////////////////////////////////////
// OpenGL related startup code is safe to put here. Load textures, etc.
void SetupRC(void)
{
GLenum err = glewInit();
if (GLEW_OK != err)
{
/* Problem: glewInit failed, something is seriously wrong. */
fprintf(stderr, "Error: %s\n", glewGetErrorString(err));
}

// Initialze Shader Manager
shaderManager.InitializeStockShaders();
glEnable(GL_DEPTH_TEST);

// Black
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

gltMakeTorus(torusBatch, 0.4f, 0.15f, 35, 35);

GLfloat alpha = 0.25f;
floorBatch.Begin(GL_TRIANGLE_FAN, 4, 1);
floorBatch.Color4f(0.0f, 1.0f, 0.0f, alpha);
floorBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
floorBatch.Normal3f(0.0, 1.0f, 0.0f);
floorBatch.Vertex3f(-20.0f, -0.41f, 20.0f);

floorBatch.Color4f(0.0f, 1.0f, 0.0f, alpha);
floorBatch.MultiTexCoord2f(0, 10.0f, 0.0f);
floorBatch.Normal3f(0.0, 1.0f, 0.0f);
floorBatch.Vertex3f(20.0f, -0.41f, 20.0f);

floorBatch.Color4f(0.0f, 1.0f, 0.0f, alpha);
floorBatch.MultiTexCoord2f(0, 10.0f, 10.0f);
floorBatch.Normal3f(0.0, 1.0f, 0.0f);
floorBatch.Vertex3f(20.0f, -0.41f, -20.0f);

floorBatch.Color4f(0.0f, 1.0f, 0.0f, alpha);
floorBatch.MultiTexCoord2f(0, 0.0f, 10.0f);
floorBatch.Normal3f(0.0, 1.0f, 0.0f);
floorBatch.Vertex3f(-20.0f, -0.41f, -20.0f);
floorBatch.End();

glGenTextures(1, textures);
glBindTexture(GL_TEXTURE_2D, textures[0]);
LoadBMPTexture("marble.bmp", GL_LINEAR_MIPMAP_LINEAR, GL_LINEAR, GL_REPEAT);

// Create blur program
blurProg = gltLoadShaderPairWithAttributes("blur.vs", "blur.fs", 2,
GLT_ATTRIBUTE_VERTEX, "vVertex", GLT_ATTRIBUTE_TEXTURE0, "texCoord0");

// Create blur textures
glGenTextures(6, blurTextures);

// ☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆
// XXX I don't think this is necessary. Should set texture data to NULL
// Allocate a pixel buffer to initialize textures and PBOs
// 计算 像素数据的字节数
pixelDataSize = screenWidth * screenHeight * 3 * sizeof(unsigned int); // XXX This should be unsigned byte
// 可以直接用 NULL 初始化 Texture
//void *data = (void *)malloc(pixelDataSize);
//memset(data, 0x00, pixelDataSize);

// Setup 6 texture units for blur effect
// Initialize texture data
for (int i = 0; i < 6; i++)
{
glActiveTexture(GL_TEXTURE1 + i);
glBindTexture(GL_TEXTURE_2D, blurTextures[i]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, screenWidth, screenHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL/*data*/);
}

// Alloc space for copying pixels so we dont call malloc on every draw
// 创建分配 PBO，并绑定为Pack Buffer，类型为GL_DYNAMIC_COPY
glGenBuffers(1, pixBuffObjs);
glBindBuffer(GL_PIXEL_PACK_BUFFER, pixBuffObjs[0]);
glBufferData(GL_PIXEL_PACK_BUFFER, pixelDataSize, pixelData, GL_DYNAMIC_COPY);
glBindBuffer(GL_PIXEL_PACK_BUFFER, 0);
// ☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆

// Create geometry and a matrix for screen aligned drawing
gltGenerateOrtho2DMat(screenWidth, screenHeight, orthoMatrix, screenQuad);

// Make sure all went well
gltCheckErrors();
}

///////////////////////////////////////////////////////////////////////////////
// Do your cleanup here. Free textures, display lists, buffer objects, etc.
void ShutdownRC(void)
{
// Make sure default FBO is bound
// 确保绑定默认的 FBO
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
glBindFramebuffer(GL_READ_FRAMEBUFFER, 0);

// Cleanup textures
for (int i = 0; i < 7; i++)
{
glActiveTexture(GL_TEXTURE0 + i);
glBindTexture(GL_TEXTURE_2D, 0);
}

// Now delete detached textures
glDeleteTextures(1, textures);
glDeleteTextures(6, blurTextures);

// delete PBO
// ☆ 删除 PBO
glDeleteBuffers(1, pixBuffObjs);
}

///////////////////////////////////////////////////////////////////////////////
// This is called at least once and before any rendering occurs. If the screen
// is a resizeable window, then this will also get called whenever the window
// is resized.
void ChangeSize(int nWidth, int nHeight)
{
glViewport(0, 0, nWidth, nHeight);
transformPipeline.SetMatrixStacks(modelViewMatrix, projectionMatrix);
viewFrustum.SetPerspective(35.0f, float(nWidth) / float(nHeight), 1.0f, 100.0f);
projectionMatrix.LoadMatrix(viewFrustum.GetProjectionMatrix());
modelViewMatrix.LoadIdentity();

// update screen sizes
screenWidth = nWidth;
screenHeight = nHeight;

// reset screen aligned quad
gltGenerateOrtho2DMat(screenWidth, screenHeight, orthoMatrix, screenQuad);

// ☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆
free(pixelData);
pixelDataSize = screenWidth * screenHeight * 3 * sizeof(unsigned int);
pixelData = (void *)malloc(pixelDataSize);

// Resize PBOs
// 如果窗口大小发生变化，则重新分配 PBO
glBindBuffer(GL_PIXEL_PACK_BUFFER, pixBuffObjs[0]);
glBufferData(GL_PIXEL_PACK_BUFFER, pixelDataSize, pixelData, GL_DYNAMIC_COPY);
glBindBuffer(GL_PIXEL_PACK_BUFFER, 0);
// ☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆☆
gltCheckErrors();
}

///////////////////////////////////////////////////////////////////////////////
// Update the camera based on user input, toggle display modes
//
void ProccessKeys(unsigned char key, int x, int y)
{
static CStopWatch cameraTimer;
float fTime = cameraTimer.GetElapsedSeconds();
float linear = fTime * 12.0f;
cameraTimer.Reset();

// Alternate between PBOs and local memory when 'P' is pressed
// 按 P键 切换 PBO和内存
if(key == 'P' || key == 'p')
bUsePBOPath = (bUsePBOPath) ? GL_FALSE : GL_TRUE;

// Speed up movement
if(key == '+')
{
speedFactor += linear / 2;
if(speedFactor > 6)
speedFactor = 6;
}

// Slow down moement
if(key == '-')
{
speedFactor -= linear / 2;
if(speedFactor < 0.5)
speedFactor = 0.5;
}
}

///////////////////////////////////////////////////////////////////////////////
// Load and setup program for blur effect
//

void SetupBlurProg(void)
{
// Set the blur program as the current one
glUseProgram(blurProg);

// Set MVP matrix
glUniformMatrix4fv(glGetUniformLocation(blurProg, "mvpMatrix"), 1, GL_FALSE, transformPipeline.GetModelViewProjectionMatrix());

// Setup the textue units for the blur targets, these rotate every frame
glUniform1i(glGetUniformLocation(blurProg, "textureUnit0"), GetBlurTarget0());
glUniform1i(glGetUniformLocation(blurProg, "textureUnit1"), GetBlurTarget1());
glUniform1i(glGetUniformLocation(blurProg, "textureUnit2"), GetBlurTarget2());
glUniform1i(glGetUniformLocation(blurProg, "textureUnit3"), GetBlurTarget3());
glUniform1i(glGetUniformLocation(blurProg, "textureUnit4"), GetBlurTarget4());
glUniform1i(glGetUniformLocation(blurProg, "textureUnit5"), GetBlurTarget5());
}

///////////////////////////////////////////////////////////////////////////////
// Draw the scene
//
void DrawWorld(GLfloat yRot, GLfloat xPos)
{
M3DMatrix44f mCamera;
modelViewMatrix.GetMatrix(mCamera);

// Need light position relative to the Camera
M3DVector4f vLightTransformed;
m3dTransformVector4(vLightTransformed, vLightPos, mCamera);

// Draw stuff relative to the camera
modelViewMatrix.PushMatrix();
modelViewMatrix.Translate(0.0f, 0.2f, -2.5f);
modelViewMatrix.Translate(xPos, 0.0f, 0.0f);
modelViewMatrix.Rotate(yRot, 0.0f, 1.0f, 0.0f);

shaderManager.UseStockShader(GLT_SHADER_POINT_LIGHT_DIFF,
modelViewMatrix.GetMatrix(),
transformPipeline.GetProjectionMatrix(),
vLightTransformed, vGreen, 0);
torusBatch.Draw();
modelViewMatrix.PopMatrix();
}

///////////////////////////////////////////////////////////////////////////////
// Render a frame. The owning framework is responsible for buffer swaps,
// flushes, etc.
void RenderScene(void)
{
static CStopWatch animationTimer;
static float totalTime = 6; // To go back and forth
static float halfTotalTime = totalTime / 2;
float seconds = animationTimer.GetElapsedSeconds() * speedFactor;
float xPos = 0;

// Calculate the next postion of the moving object
// First perform a mod-like operation on the time as a float
while(seconds > totalTime)
seconds -= totalTime;

// Move object position, if it's gone half way across
// start bringing it back
if(seconds < halfTotalTime)
xPos = seconds - halfTotalTime * 0.5f;
else
xPos = totalTime - seconds - halfTotalTime * 0.5f;

// First draw world to screen
modelViewMatrix.PushMatrix();
M3DMatrix44f mCamera;
cameraFrame.GetCameraMatrix(mCamera);
modelViewMatrix.MultMatrix(mCamera);

glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, textures[0]); // Marble
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
shaderManager.UseStockShader(GLT_SHADER_TEXTURE_MODULATE, transformPipeline.GetModelViewProjectionMatrix(), vWhite, 0);

floorBatch.Draw();
DrawWorld(0.0f, xPos);
modelViewMatrix.PopMatrix();

if(bUsePBOPath)
{
// First bind the PBO as the pack buffer, then read the pixels directly to the PBO
// ☆ 首先绑定 PBO 为 Pack Buffer，再直接从 Frame Buffer 中读取像素到 PBO ☆
glBindBuffer(GL_PIXEL_PACK_BUFFER, pixBuffObjs[0]);
glReadPixels(0, 0, screenWidth, screenHeight, GL_RGB, GL_UNSIGNED_BYTE, NULL);
glBindBuffer(GL_PIXEL_PACK_BUFFER, 0); // 解绑 PBO

// Next bind the PBO as the unpack buffer, then push the pixels straight into the texture
// ☆ 接着绑定 PBO 为 Unpack Buffer，再把 PBO 中的像素直接推送到纹理当中 ☆
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, pixBuffObjs[0]);

// Setup texture unit for new blur, this gets imcremented every frame
glActiveTexture(GL_TEXTURE0 + GetBlurTarget0() );
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8, screenWidth, screenHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0); // 解绑 PBO
}
else
{
// Grab the screen pixels and copy into local memory
// 从FrameBuffer中获取屏幕像素，并拷贝到客户端内存中
glReadPixels(0, 0, screenWidth, screenHeight, GL_RGB, GL_UNSIGNED_BYTE, pixelData);

// Push pixels from client memory into texture
// Setup texture unit for new blur, this gets imcremented every frame
// 推送客户端内存中的像素到纹理中
glActiveTexture(GL_TEXTURE0 + GetBlurTarget0() );
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8, screenWidth, screenHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, pixelData);
}

// Draw full screen quad with blur shader and all blur textures
projectionMatrix.PushMatrix();
projectionMatrix.LoadIdentity();
projectionMatrix.LoadMatrix(orthoMatrix);
modelViewMatrix.PushMatrix();
modelViewMatrix.LoadIdentity();
glDisable(GL_DEPTH_TEST);
SetupBlurProg();
screenQuad.Draw();
glEnable(GL_DEPTH_TEST);
modelViewMatrix.PopMatrix();
projectionMatrix.PopMatrix();

// Move to the next blur texture for the next frame
AdvanceBlurTaget();

// Do the buffer Swap
glutSwapBuffers();

// Do it again
glutPostRedisplay();

UpdateFrameCount();
}

int main(int argc, char *argv[])
{
screenWidth = 800;
screenHeight = 600;
bFullScreen = false;
bAnimated = true;
bUsePBOPath = false; // true
blurProg = 0;
speedFactor = 1.0f;

gltSetWorkingDirectory(argv[0]);

glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(screenWidth, screenHeight);

glutCreateWindow("Pix Buffs");

glutReshapeFunc(ChangeSize);
glutDisplayFunc(RenderScene);
glutKeyboardFunc(ProccessKeys);

SetupRC();
glutMainLoop();
ShutdownRC();

return 0;
}

执行效果图：



相关阅读：OpenGL深入探索——像素缓冲区对象 （PBO）