if (aSImage[i] != aS2Image[i]) {
if (aSImage[i] == aS2Image[i]) {
static void Do8Blend(float aOpacity, PRInt32 aNumLines, PRInt32 aNumBytes,                     PRUint8 *aSImage, PRUint8 *aS2Image, PRUint8 *aDImage,                     PRInt32 aSLSpan, PRInt32 aDLSpan){  if (aOpacity <= 0.0) {    return;  }  // OK, just do an opaque blend. Assume the rendered image had just  // 1-bit alpha.  PRIntn y;  if (!aS2Image) {    for (y = 0; y < aNumLines; y++) {      memcpy(aDImage, aSImage, aNumBytes);      aSImage += aSLSpan;      aDImage += aDLSpan;    }  } else {    for (y = 0; y < aNumLines; y++) {      for (int i = 0; i < aNumBytes; i++) {        if (aSImage[i] != aS2Image[i]) {          aDImage[i] = aSImage[i];        }      }      aSImage += aSLSpan;      aS2Image += aSLSpan;      aDImage += aDLSpan;    }  }}