RLE-BMP 利用一维行程编码压缩8位BMP

其中关键函数是将输入的 pSrcBits数组利用游程编码进行压缩，输出结果数组pRLEBits。需要注意的是判断当前指针是否处在行末的位置。 函数体中有state_start；state_compress；state_no_compress；end_of_line四个状态。 void CDVDBitmapControl::CompressInRLE8(BYTE* pSrcBits, CByteArray& pRLEBits, int& RLE_size) { int line; int src_index = 0, dst_index = 0, counter, i; // in RLE8 every pixel is one byte for ( line = 0; line < m_dib.dsBmih.biHeight; line++) { state_start: // just at the start of a block if ( EndOfLine(src_index)) // this is the last pixel of the line { pRLEBits[dst_index++] = 1; // block of length 1 pRLEBits[dst_index++] = pSrcBits[src_index]; src_index++; goto end_of_line; } // now the block length is at least 2, look ahead to decide next state // next two same pixels are the same, enter compress mode if (pSrcBits[src_index] == pSrcBits[src_index+1]) goto state_compress; if ( EndOfLine(src_index+1)) // the last 2 pixel of the line { // these 2 pixel are not the same pRLEBits[dst_index++] = 1; // block of length 1 pRLEBits[dst_index++] = pSrcBits[src_index++]; pRLEBits[dst_index++] = 1; // block of length 1 pRLEBits[dst_index++] = pSrcBits[src_index++]; goto end_of_line; } // now the block length is at least 3 // in next 3 pixels, the last 2 consecutive pixel are the same if (pSrcBits[src_index+1] == pSrcBits[src_index+2]) { pRLEBits[dst_index++] = 1; // block of length 1 pRLEBits[dst_index++] = pSrcBits[src_index++]; goto state_compress; } else // in these 3 pixel, no 2 consecutive pixel are the same goto state_no_compress; // un-compressed block need at least 3 pixel state_compress: // compress mode // src_index is the first pixel of a compressd block // counter is the number of additional pixels following currrent pixel // (src_index+counter) point to the last pixel of current block for ( counter = 1; counter <= 254; counter++) { // must check this condition first, or a BUG occur! if ( pSrcBits[src_index+counter] != pSrcBits[src_index] ) break; if ( EndOfLine(src_index+counter) ) // reach end of line { pRLEBits[dst_index++] = counter+1; // block length is (counter+1) pRLEBits[dst_index++] = pSrcBits[src_index]; src_index += counter +1; goto end_of_line; } } // now pSrcBits[src_index+counter] falls out of block pRLEBits[dst_index++] = counter; // block length is (counter) pRLEBits[dst_index++] = pSrcBits[src_index]; src_index += counter; goto state_start; state_no_compress: // src_index is the first pixel of a un-compressd block // un-compressed block need at least 3 pixel // counter is the number of additional pixels following currrent pixel for (counter = 2; counter <= 254; counter++) { if ( EndOfLine(src_index+counter) ) // reach end of line { pRLEBits[dst_index++] = 0; // escape character for un-compress block pRLEBits[dst_index++] = counter + 1; // block length is (counter+1) for (i = counter + 1; i > 0; i--) pRLEBits[dst_index++] = pSrcBits[src_index++]; if ( 0 != ((counter+1) % 2) ) // block length is odd pRLEBits[dst_index++]; // padd with a zero byte goto end_of_line; } if ( EndOfLine(src_index+counter+1) || pSrcBits[src_index+counter] != pSrcBits[src_index+counter+1] ) continue; // still no 2 consecutive pixel are the same, // therefore continue to extend the un-compress block // we found two pixels are the same if ( EndOfLine(src_index+counter+2) || pSrcBits[src_index+counter+1] != pSrcBits[src_index+counter+2] ) continue; // the third pixel is not the same, no need to exit un-compressed mode else { // // now pSrcBits[src_index+counter] and following 2 pixel are the same // now we need to exit the un-compressed mode if ( counter > 2) counter--; // we can shrink the block one pixel (go backward) pRLEBits[dst_index++] = 0; // escape character for un-compress block pRLEBits[dst_index++] = counter+1; // block length is (counter+1) for (i = counter+1; i > 0; i--) pRLEBits[dst_index++] = pSrcBits[src_index++]; if ( 0 != ((counter+1) % 2) ) // block length is odd pRLEBits[dst_index++]; // padd with a zero byte goto state_compress; } } // end of for (counter = 2; counter <= 254; counter++) // now we have a full block of 255 pixels pRLEBits[dst_index++] = 0; // escape character for un-compress block pRLEBits[dst_index++] = counter; // block length is (counter) for (i = counter; i > 0; i--) pRLEBits[dst_index++] = pSrcBits[src_index++]; if ( 0 != ((counter) % 2) ) // block length is odd pRLEBits[dst_index++]; // padd with a zero byte goto state_start; end_of_line: if ( 0 != (src_index % 4 )) // each scan line is dword align { int pad = 4 - (src_index%4); src_index += pad; } // src_index already point to the start of next line pRLEBits[dst_index++] = 0; // mark end-of-line pRLEBits[dst_index++] = 0; } pRLEBits[dst_index++] = 0; // mark end-of-bitmap pRLEBits[dst_index++] = 1; RLE_size = dst_index; // image size }