Performance of glReadPixels and CopyBits
- glReadPixels:
30 times capture cost 542303875.000000 nanoseconds; -542303 microseconds.size_t bitsPerPixel = CGBitmapContextGetBitsPerPixel( context ) ;
size_t width = CGBitmapContextGetWidth( context ) ;
size_t height = CGBitmapContextGetHeight( context ) ;
size_t bytewidth = CGBitmapContextGetBytesPerRow( context );time1 = UpTime();
for ( i = 0 ;i
glReadPixels( 0, 0, width, height, GL_BGRA, packedPixelFormat, data);
time2 = UpTime();
nanosec = AbsoluteDeltaToNanoseconds(time2,time1);
duration = AbsoluteDeltaToDuration(time2,time1);
nanodouble = ConvertNanosecondsToDouble ( &nanosec);
printf(" %d times capture cost %f nanoseconds; %ld milliseconds.\n",i,nanodouble, duration); - CopyBits:
30 times capture cost 3910429766.000000 nanoseconds; -3910429 microseconds.
mainDevice = GetMainDevice();
/* Store its current pixel depth. */
depth = (**(**mainDevice).gdPMap).pixelSize;/* Make an identical copy of its pixmap's colortable. */
cTable = (**(**mainDevice).gdPMap).pmTable;
(void) HandToHand( (Handle*)(&cTable) );bytesPerRow = ((gBounds.right - gBounds.left) * depth) / 8;
offBaseAddr = NewPtr((unsigned long)bytesPerRow * (gBounds.bottom - gBounds.top));gPixMap.baseAddr = offBaseAddr; /* Point to image */
gPixMap.rowBytes = bytesPerRow | 0x8000; /* MSB set for PixMap */
gPixMap.bounds = gBounds; /* Use given bounds */
gPixMap.pmVersion = 0; /* No special stuff */
gPixMap.packType = 0; /* Default PICT pack */
gPixMap.packSize = 0; /* Always zero in mem */
gPixMap.hRes = 72; /* 72 DPI default res */
gPixMap.vRes = 72; /* 72 DPI default res */
gPixMap.pixelSize = depth; /* Set # bits/pixel */
//gPixMap.planeBytes = 0; /* Not used */
//gPixMap.pmReserved = 0; /* Not used */gPixMap.pixelType = 0; /* Indicates indexed */
gPixMap.cmpCount = 1; /* Have 1 component */
gPixMap.cmpSize = depth; /* Component size=depth */
gPixMap.pmTable = cTable; /* Handle to CLUT */startTime = UpTime();
for (i = 0 ;i
CopyBits( (BitMap *)*(**mainDevice).gdPMap, (BitMap *)(&gPixMap),
&(**(**mainDevice).gdPMap).bounds, &gPixMap.bounds, srcCopy, 0l );
endTime = UpTime();
nano = AbsoluteDeltaToNanoseconds(endTime,startTime) ;
duration = AbsoluteDeltaToDuration(endTime,startTime);
nanodouble = ConvertNanosecondsToDouble ( &nano );
printf(" %d times capture cost %f nanoseconds; %ld milliseconds.\n",i,nanodouble, duration);
run on
Hardware Overview:
Machine Name: MacBook
Machine Model: MacBook1,1
Processor Name: Intel Core Duo
Processor Speed: 1.83 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache (per processor): 2 MB
Memory: 1 GB
Bus Speed: 667 MHz
Screen Size: 1152×720, Millions
Waiting for the wind 
6 十一月, 2006 於 6:15 上午
30 times of calling CapScreenFetchdataToContext spends -539964 milliseconds
30 times of calling CapScreenFetchdataToContextFast spends -545436 milliseconds
int CapScreenFetchDataToContextFast(CGContextRef context, void * data, size_t width, size_t height,size_t bytewidth, GLenum packedPixelFormat )
{
if ( context == NULL)
return -1;
if ( data == NULL)
return -2;
glReadPixels( 0, 0, width, height,
GL_BGRA,
packedPixelFormat,
data);
}
int CapScreenFetchDataToContext ( CGContextRef context)
{
if ( context == NULL)
return -1;
GLenum packedPixelFormat ;
size_t bitsPerPixel = CGBitmapContextGetBitsPerPixel( context ) ;
size_t width = CGBitmapContextGetWidth( context ) ;
size_t height = CGBitmapContextGetHeight( context ) ;
size_t bytewidth = CGBitmapContextGetBytesPerRow( context );
void * data = CGBitmapContextGetData( context);
if ( data == NULL)
return -2;
switch ( bitsPerPixel)
{
case 16:
packedPixelFormat = GL_UNSIGNED_SHORT_5_5_5_1 ;
break;
case 32:
packedPixelFormat = GL_UNSIGNED_INT_8_8_8_8 ;
break;
default:
return -3;
}
/*
* Fetch the data in XRGB format, matching the bitmap context.
*/
glReadPixels( 0, 0, width, height, GL_BGRA, packedPixelFormat, 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);
}
6 十一月, 2006 於 6:36 上午
AbsoluteDeltaToDuration(a,b) returns nagative values in microseconds.