写下来从iPhone上的屏幕外FBO阅读; 适用于模拟器但不适用于设备？

Question

我试图在iPhone上进行一些图像处理,基于Apple的GLImageProcessing示例.

最后,我想要做的是将图像加载到纹理中,执行示例代码中的一个或多个操作(色调,饱和度,亮度等),然后将结果图像读回以供以后处理/保存.在大多数情况下,这永远不需要触摸屏幕,所以我认为FBO可能是要走的路.

首先,我拼凑了一个小例子,创建一个屏幕外FBO,绘制它,然后将数据作为图像读回.当它在模拟器中完美运行时我感到很兴奋,然后因为我意识到我在实际设备上只有一个黑屏而感到沮丧.

免责声明:我的OpenGL已经足够老了,我已经对OpenGL ES有了相当多的学习曲线,而且我从来都不是一个纹理向导.我知道该设备在帧缓冲访问方面具有与模拟器不同的特性(强制性的屏幕外FBO和设备上的交换,模拟器上的直接访问),但我无法找到我做错了什么,即使经过相当广泛的搜索.

有什么建议？

// set up the offscreen FBO sizes

int renderBufferWidth = 1280;
int renderBufferHeight = 720;

// now the FBO
GLuint  fbo = 0;
glGenFramebuffersOES(1, &fbo);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, fbo);

GLuint  renderBuffer = 0;
glGenRenderbuffersOES(1, &renderBuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, renderBuffer);
glRenderbufferStorageOES(GL_RENDERBUFFER_OES,
                         GL_RGBA8_OES,
                         renderBufferWidth,
                         renderBufferHeight);

glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES,
                             GL_COLOR_ATTACHMENT0_OES,
                             GL_RENDERBUFFER_OES,
                             renderBuffer);

GLenum status = glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES);
if (status != GL_FRAMEBUFFER_COMPLETE_OES) {
    NSLog(@"Problem with OpenGL framebuffer after specifying color render buffer: %x", status);
}

// throw in a test drawing  
glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);


static const GLfloat triangleVertices[] = {
    -0.5f,  -0.33f,
    0.5f,  -0.33f,
    -0.5f,   0.33f
};

static const GLfloat triangleColors[] = {
    1.0, 0.0, 0.0, 0.5,
    0.0, 1.0, 0.0, 0.5,
    0.0, 0.0, 1.0, 0.5
};

GLint backingWidth = 320;
GLint backingHeight = 480;

NSLog(@"setting up view/model matrices");
glMatrixMode(GL_PROJECTION);
glLoadIdentity();

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();


glVertexPointer(2, GL_FLOAT, 0, triangleVertices);
glEnableClientState(GL_VERTEX_ARRAY);
glColorPointer(4, GL_FLOAT, 0, triangleColors);
glEnableClientState(GL_COLOR_ARRAY);



// draw the triangle
glDrawArrays(GL_TRIANGLE_STRIP, 0, 3);


// Extract the resulting rendering as an image
int samplesPerPixel = 4; // R, G, B and A
int rowBytes = samplesPerPixel * renderBufferWidth;
char* bufferData = (char*)malloc(rowBytes * renderBufferHeight);
if (bufferData == NULL) {
    NSLog(@"Unable to allocate buffer for image extraction.");
}

// works on simulator with GL_BGRA, but not on device
glReadPixels(0, 0, renderBufferWidth,
             renderBufferHeight,
             GL_BGRA,
             GL_UNSIGNED_BYTE, bufferData);
NSLog(@"reading pixels from framebuffer");

// Flip it vertically - images read from OpenGL buffers are upside-down
char* flippedBuffer = (char*)malloc(rowBytes * renderBufferHeight);
if (flippedBuffer == NULL) {
    NSLog(@"Unable to allocate flipped buffer for corrected image.");
}

for (int i = 0 ; i < renderBufferHeight ; i++) {   
    bcopy(bufferData + i * rowBytes,
          flippedBuffer + (renderBufferHeight - i - 1) * rowBytes,
          rowBytes);
}

// unbind my FBO
glBindFramebufferOES(GL_FRAMEBUFFER_OES, 0);

// Output the image to a file


CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
int bitsPerComponent = 8;

CGBitmapInfo bitmapInfo = kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Host;
CGContextRef contextRef = CGBitmapContextCreate(flippedBuffer,
                                                renderBufferWidth,
                                                renderBufferHeight,
                                                bitsPerComponent,
                                                rowBytes, colorSpace, bitmapInfo);
if (contextRef == nil) {
    NSLog(@"Unable to create CGContextRef.");
}

CGImageRef imageRef = CGBitmapContextCreateImage(contextRef);

if (imageRef == nil) {
    NSLog(@"Unable to create CGImageRef.");
} else {
    if (savedImage == NO) {
        UIImage *myImage = [UIImage imageWithCGImage:imageRef];
        UIImageWriteToSavedPhotosAlbum(myImage, nil, nil, nil);
        savedImage = YES;
    }   
}

编辑:

答案当然是位图格式应该是GL_RGBA,而不是GL_BGRA:

// works on simulator with GL_BGRA, but not on device
glReadPixels(0, 0, renderBufferWidth,
         renderBufferHeight,
         **GL_RGBA**,
         GL_UNSIGNED_BYTE, bufferData);

Answer 1

正如安德鲁自己回答的那样：

\n\n

答案是位图格式应该是 GL_RGBA，而不是 GL_BGRA

\n\n

// works on simulator with GL_BGRA, but not on device\nglReadPixels(0, 0, renderBufferWidth,\n\xc2\xa0 \xc2\xa0 \xc2\xa0 \xc2\xa0 \xc2\xa0    renderBufferHeight,\n\xc2\xa0 \xc2\xa0 \xc2\xa0 \xc2\xa0 \xc2\xa0    GL_RGBA, // <--\n\xc2\xa0 \xc2\xa0 \xc2\xa0 \xc2\xa0 \xc2\xa0    GL_UNSIGNED_BYTE, bufferData);\n

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