#define SWAP_IMAGES(idx0, idx1) \
	vgCopyImage(tmpImage, 0, 0, imgChildren[idx0], 0, 0, 64, 64, VG_FALSE); \
	vgCopyImage(imgChildren[idx0], 0, 0, imgChildren[idx1], 0, 0, 64, 64, VG_FALSE); \
	vgCopyImage(imgChildren[idx1], 0, 0, tmpImage, 0, 0, 64, 64, VG_FALSE);

// create image and load external data
imgSrc = vgCreateImage(VG_lRGBA_8888, imgGirlAlphaWidth, imgGirlAlphaHeight, VG_IMAGE_QUALITY_NONANTIALIASED);
vgImageSubData(imgSrc, (const void *)imgGirlAlphaData, imgGirlAlphaDataStride, imgGirlAlphaFormat, 0, 0, imgGirlAlphaWidth, imgGirlAlphaHeight);

// create a temporary image, used for swap
tmpImage = vgCreateImage(VG_lRGBA_8888, 64, 64, VG_IMAGE_QUALITY_NONANTIALIASED);

k = 0;
for (i = 0; i < 4; ++i)
	for (j = 0; j < 4; ++j)
		imgChildren[k++] = vgChildImage(imgSrc, j * 64, i * 64, 64, 64);

SWAP_IMAGES(0, 13)
SWAP_IMAGES(7, 8)
SWAP_IMAGES(5, 15)
SWAP_IMAGES(10, 3)
SWAP_IMAGES(2, 14)
SWAP_IMAGES(1, 4)
SWAP_IMAGES(6, 12)
SWAP_IMAGES(9, 11)

imgParent = vgGetParent(imgChildren[8]);
vgGetImageSubData(imgParent, imgOutputDataRGBA, imgGirlAlphaDataStride, imgGirlAlphaFormat, 0, 0, imgGirlAlphaWidth, imgGirlAlphaHeight);
strcpy(imgFileName, "image_children_swap.png");
saveImage32(f, imgFileName, "Create and swap 16 child images.", imgGirlAlphaWidth, imgGirlAlphaHeight, imgOutputDataRGBA, 0);


// clear a new child image
imgChildren[16] = vgChildImage(imgSrc, 64, 64, 128, 128);
col[0] = 0.1f; col[1] = 0.3f; col[2] = 0.7f; col[3] = 1.0f;
vgSetfv(VG_CLEAR_COLOR, 4, col);
vgClearImage(imgChildren[16], -32, -32, 192, 192);

imgParent = vgGetParent(imgChildren[16]);
vgGetImageSubData(imgParent, imgOutputDataRGBA, imgGirlAlphaDataStride, imgGirlAlphaFormat, 0, 0, imgGirlAlphaWidth, imgGirlAlphaHeight);
strcpy(imgFileName, "image_children_clear.png");
saveImage32(f, imgFileName, "Clear a child image.", imgGirlAlphaWidth, imgGirlAlphaHeight, imgOutputDataRGBA, 0);


// destroy images
for (k = 0; k < 17; ++k)
	vgDestroyImage(imgChildren[k]);
vgDestroyImage(imgSrc);
vgDestroyImage(tmpImage);

#undef SWAP_IMAGES