我正在使用glgrab代码尝试获取Mac屏幕的全屏截图。但是,我希望位图数据采用GL_RGB格式。也就是说,每个像素应采用以下格式:
0x00RRGGBB
原始代码指定了GL_BGRA
格式。但是,将其更改为GL_RGB
会给我一个完全空白的结果。我正在使用的总源代码是:
CGImageRef grabViaOpenGL(CGDirectDisplayID display, CGRect srcRect)
{
CGContextRef bitmap;
CGImageRef image;
void * data;
long bytewidth;
GLint width, height;
long bytes;
CGColorSpaceRef cSpace = CGColorSpaceCreateWithName (kCGColorSpaceGenericRGB);
CGLContextObj glContextObj;
CGLPixelFormatObj pixelFormatObj ;
GLint numPixelFormats ;
//CGLPixelFormatAttribute
int attribs[] =
{
// kCGLPFAClosestPolicy,
kCGLPFAFullScreen,
kCGLPFADisplayMask,
NULL, /* Display mask bit goes here */
kCGLPFAColorSize, 24,
kCGLPFAAlphaSize, 0,
kCGLPFADepthSize, 32,
kCGLPFASupersample,
NULL
} ;
if ( display == kCGNullDirectDisplay )
display = CGMainDisplayID();
attribs[2] = CGDisplayIDToOpenGLDisplayMask(display);
/* Build a full-screen GL context */
CGLChoosePixelFormat( (CGLPixelFormatAttribute*) attribs, &pixelFormatObj, &numPixelFormats );
if ( pixelFormatObj == NULL ) // No full screen context support
{
// GL didn't find any suitable pixel formats. Try again without the supersample bit:
attribs[10] = NULL;
CGLChoosePixelFormat( (CGLPixelFormatAttribute*) attribs, &pixelFormatObj, &numPixelFormats );
if (pixelFormatObj == NULL)
{
qDebug("Unable to find an openGL pixel format that meets constraints");
return NULL;
}
}
CGLCreateContext( pixelFormatObj, NULL, &glContextObj ) ;
CGLDestroyPixelFormat( pixelFormatObj ) ;
if ( glContextObj == NULL )
{
qDebug("Unable to create OpenGL context");
return NULL;
}
CGLSetCurrentContext( glContextObj ) ;
CGLSetFullScreen( glContextObj ) ;
glReadBuffer(GL_FRONT);
width = srcRect.size.width;
height = srcRect.size.height;
bytewidth = width * 4; // Assume 4 bytes/pixel for now
bytewidth = (bytewidth + 3) & ~3; // Align to 4 bytes
bytes = bytewidth * height; // width * height
/* Build bitmap context */
data = malloc(height * bytewidth);
if ( data == NULL )
{
CGLSetCurrentContext( NULL );
CGLClearDrawable( glContextObj ); // disassociate from full screen
CGLDestroyContext( glContextObj ); // and destroy the context
qDebug("OpenGL drawable clear failed");
return NULL;
}
bitmap = CGBitmapContextCreate(data, width, height, 8, bytewidth,
cSpace, kCGImageAlphaNoneSkipFirst /* XRGB */);
CFRelease(cSpace);
/* Read framebuffer into our bitmap */
glFinish(); /* Finish all OpenGL commands */
glPixelStorei(GL_PACK_ALIGNMENT, 4); /* Force 4-byte alignment */
glPixelStorei(GL_PACK_ROW_LENGTH, 0);
glPixelStorei(GL_PACK_SKIP_ROWS, 0);
glPixelStorei(GL_PACK_SKIP_PIXELS, 0);
/*
* Fetch the data in XRGB format, matching the bitmap context.
*/
glReadPixels((GLint)srcRect.origin.x, (GLint)srcRect.origin.y, width, height,
GL_RGB,
#ifdef __BIG_ENDIAN__
GL_UNSIGNED_INT_8_8_8_8_REV, // for PPC
#else
GL_UNSIGNED_INT_8_8_8_8, // for Intel! http://lists.apple.com/archives/quartz-dev/2006/May/msg00100.html
#endif
data);
/*
* glReadPixels generates a quadrant I raster, with origin in the lower left
* This isn't a problem for signal processing routines such as compressors,
* as they can simply use a negative 'advance' to move between scanlines.
* CGImageRef and CGBitmapContext assume a quadrant III raster, though, so we need to
* invert it. Pixel reformatting can also be done here.
*/
swizzleBitmap(data, bytewidth, height);
/* Make an image out of our bitmap; does a cheap vm_copy of the bitmap */
image = CGBitmapContextCreateImage(bitmap);
/* Get rid of bitmap */
CFRelease(bitmap);
free(data);
/* Get rid of GL context */
CGLSetCurrentContext( NULL );
CGLClearDrawable( glContextObj ); // disassociate from full screen
CGLDestroyContext( glContextObj ); // and destroy the context
/* Returned image has a reference count of 1 */
return image;
}
我是OpenGL的新手,所以我很欣赏正确方向的一些指示。干杯!
更新:
经过一些实验,我设法缩小了我的问题。我的问题是,虽然我不想要alpha组件,但我希望每个像素都打包到4字节边界。现在,当我为glReadPixels
调用指定GL_RGB或GL_BGR格式时,我得到以3字节块打包的位图数据。当我指定GL_RGBA
或GL_BGRA
时,我得到四个字节的块,但最后总是使用alpha通道组件。
然后我尝试更改传递给
的值 bitmap = CGBitmapContextCreate(data, width, height, 8, bytewidth,cSpace, kCGImageAlphaNoneSkipFirst /* XRGB */);
但是,AlphaNoneSkipFirst
或AlphaNoneSkipLast
的变体不会将Alpha通道置于像素字节块的开头。
有什么想法吗?
答案 0 :(得分:2)
我不是Mac家伙,但是如果你能获得RGBA数据并且想要XRGB,那么你不能将每个像素按位移位8位吗?
foreach( unsigned int* RGBA_pixel, pixbuf )
{
(*RGBA_pixel) = (*RGBA_pixel) >> 8;
}
答案 1 :(得分:1)
尝试使用GL_UNSIGNED_BYTE
代替GL_UNSIGNED_INT_8_8_8_8_REV
/ GL_UNSIGNED_INT_8_8_8_8
。
虽然您似乎想要 GL_RGBA ,但它应该适用于8_8_8_8_REV或8_8_8_8。
答案 2 :(得分:0)
当我使用GL_BGRA时,数据会被预先调整返回,这是因为当我在窗口中显示结果时,颜色看起来是正确的。
如果您想要我创建的项目,请与我联系。希望这会有所帮助。