我从着色器存储缓冲区读回数据后得到的帧速率非常低，即使我只读取一次数据。
这就是我绑定它的方式：
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, posBuf);
glBufferData(GL_SHADER_STORAGE_BUFFER, numPoints*4* sizeof(GLfloat),&points[0][0], GL_DYNAMIC_Draw);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, NULL);
并阅读：
GLfloat * temp = new GLfloat[numPoints*4];
glBindBuffer(GL_SHADER_STORAGE_BUFFER, posBuf);
glGetBufferSubData(GL_SHADER_STORAGE_BUFFER, 0, numPoints* 4 * sizeof(GLfloat), temp);
glBindBuffer( GL_SHADER_STORAGE_BUFFER, 0 );
在帧速率从200下降到15之后执行此操作。
有什么办法可以避免吗？
谢谢！
答案 0 :(得分：0)
对不起该语言，但这是保存.PNG文件的Objective C方法的快速直接复制。我相信你可以收集显着的代码。
// ****************************************** High Resolution Image With Alpha *********************************************
- (void) saveHiResFileWithAlpha
{
// ************************************** Save the Current Viewport Size
GLint screenViewPort[4];
glGetIntegerv(GL_VIEWPORT, screenViewPort);
// ***************************** Define a Second Output Buffer and Bind it for Writing
glGenFramebuffersEXT(1, wispSecondOutputBuffer);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, wispSecondOutputBuffer[0]);
// ******************************* Set the Viewport to the Texture Size and Reshape
glViewport(0,0,TEXTUREWIDTH, TEXTUREHEIGHT); // Texture is 6000 X 4000
[self resizeTextureGL]; // Calculate Model View and Projection Matrices
// ************************************** Create the Output Imgage Texture
glGenTextures( 1, wispOutputTexture);
glBindTexture(GL_TEXTURE_2D, wispOutputTexture[0]);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, (GLsizei)TEXTUREWIDTH, (GLsizei)TEXTUREHEIGHT, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
// ********************************* Attach the Output Texture to the Frame Buffer
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, wispOutputTexture[0], 0);
GLenum DrawBuffers[1] = {GL_COLOR_ATTACHMENT0};
glDrawBuffers(1, DrawBuffers);
// ************************************ Check that the Frame Buffer is Complete
GLenum frameBufferStatus;
frameBufferStatus = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT);
if(frameBufferStatus != GL_FRAMEBUFFER_COMPLETE_EXT) NSLog(@"There is a problem with the output frame buffer");
// ****************************************** Render to the Texture
[self runTextureShaders]; // Render the image
[self runTextureShaders2];
// ************************************ Reset the Viewport and Frame Buffer
glViewport(screenViewPort[0],screenViewPort[1],(GLsizei)screenViewPort[2], (GLsizei)screenViewPort[3]);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
// ***************************************** Create a bitmap Image Rep
NSBitmapImageRep* bitmapImageRep = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes:(unsigned char **)NULL
pixelsWide:(int)TEXTUREWIDTH
pixelsHigh:(int)TEXTUREHEIGHT
bitsPerSample:(int)8
samplesPerPixel:(int)4
hasAlpha:(BOOL)YES
isPlanar:(BOOL)NO
colorSpaceName:(NSString *)NSDeviceRGBColorSpace
bytesPerRow:(int)(TEXTUREWIDTH * sizeof(AlphaPixelBytes))
bitsPerPixel:(int)0];
// ******************************* Copy the Texture Data Into the Bitmap Image
glBindTexture(GL_TEXTURE_2D, wispOutputTexture[0]);
glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA, GL_UNSIGNED_BYTE, bitmapImageRep.bitmapData);
// ******************************* Multiply the RGB data by the Alpha Component
AlphaPixelBytes *outputPixel = (AlphaPixelBytes*)[bitmapImageRep bitmapData];
float floatOutputPixel, floatOutputAlpha;
for(int i = 0; i < NUMTEXTUREPOINTS; i++)
{
floatOutputAlpha = (float)outputPixel[i].alpha / 255.0;
floatOutputPixel = (float)outputPixel[i].red * floatOutputAlpha;
outputPixel[i].red = (unsigned char) floatOutputPixel;
floatOutputPixel = (float)outputPixel[i].green * floatOutputAlpha;
outputPixel[i].green = (unsigned char) floatOutputPixel;
floatOutputPixel = (float)outputPixel[i].blue * floatOutputAlpha;
outputPixel[i].blue = (unsigned char) floatOutputPixel;
}
// ********************************************* Set the File Name
NSMutableString *highResPath = [NSMutableString stringWithString:appController->appDelegate->fileLoaded];
NSUInteger fileNameLength = highResPath.length;
NSRange deleteRange;
deleteRange.location = fileNameLength-3;
deleteRange.length = 3;
[highResPath deleteCharactersInRange:deleteRange];
[highResPath appendString:@"png"];
// ******************************************* Set the Save Panel
NSSavePanel *fileSavePanel = [NSSavePanel savePanel];
NSArray* allowedFileTypes = [[NSArray alloc] initWithObjects:@"png", nil];
NSURL *saveDirectoryURL = [NSURL fileURLWithPath:appController->appDelegate->wispUserImageFileDirectory isDirectory:YES];
[fileSavePanel setAllowedFileTypes:allowedFileTypes];
[fileSavePanel setTitle:@"Wisp3D File Manager"];
[fileSavePanel setNameFieldStringValue:highResPath];
[fileSavePanel setDirectoryURL:saveDirectoryURL];
// *********************************** Write the Data Out to Disk - No Compression
NSDictionary *imageProps = [NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:1.0]
forKey: NSImageCompressionFactor];
NSData *outputImageData = [bitmapImageRep representationUsingType: NSPNGFileType properties:imageProps];
NSUInteger result = [fileSavePanel runModal];
if (result == NSFileHandlingPanelOKButton)
{
BOOL saveStatus = NO;
NSURL *theFile = [fileSavePanel URL];
// ********************************** Update the Default Directory
NSString *theNewFileName = [NSString stringWithString:[theFile lastPathComponent]];
NSUInteger theNewFileLength = theNewFileName.length;
NSMutableString *theNewPath = [NSMutableString stringWithString:[theFile path]];
NSUInteger theNewPathLength = theNewPath.length;
deleteRange.location = theNewPathLength-theNewFileLength-1;
deleteRange.length = theNewFileLength+1;
[theNewPath deleteCharactersInRange:deleteRange];
[appController->appDelegate->wispUserImageFileDirectory setString:theNewPath];
// ***************************************** Write the File
saveStatus = [outputImageData writeToURL:theFile atomically:YES];
NSAlert *fileSavedAlert = [[NSAlert alloc] init];
[fileSavedAlert addButtonWithTitle:@"OK"];
if(saveStatus)
{
[fileSavedAlert setMessageText:@"File Save was Successful"];
}else{
[fileSavedAlert setMessageText:@"File Save failed"];
}
[fileSavedAlert runModal];
}
// ******************************************* Cleanup Memory
glDeleteTextures(1, wispOutputTexture);
glDeleteFramebuffersEXT(1, wispSecondOutputBuffer);
return;
}
AlphaPixelBytes定义为：
typedef struct
{
unsigned char red;
unsigned char green;
unsigned char blue;
unsigned char alpha;
} AlphaPixelBytes;
答案 1 :(得分：0)
我在使用glGetBufferSubData之前将数据复制到GL_COPY_READ_BUFFER。它工作，我没有帧速率下降。我仍然不明白为什么，但至少它是有效的...非常感谢你的帮助！
glBindBuffer(GL_SHADER_STORAGE_BUFFER, _positionBuffer);
glBindBuffer(GL_COPY_READ_BUFFER, _outputBuffer);
glCopyBufferSubData(GL_SHADER_STORAGE_BUFFER, GL_COPY_READ_BUFFER,0,0, _vertexCount* 4 * sizeof(GLfloat));
GLfloat temp [_vertexCount][4];
glBindBuffer(GL_COPY_READ_BUFFER, _outputBuffer);
glGetBufferSubData(GL_COPY_READ_BUFFER, 0, _vertexCount* 4 * sizeof(GLfloat), &temp[0][0]);
glBindBuffer( GL_COPY_READ_BUFFER, NULL );
glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);
glBindBuffer(GL_COPY_READ_BUFFER, 0);