diff options
Diffstat (limited to 'lodepng_util.cpp')
| -rw-r--r-- | lodepng_util.cpp | 24 |
1 files changed, 15 insertions, 9 deletions
diff --git a/lodepng_util.cpp b/lodepng_util.cpp index 5c5d876..899a49d 100644 --- a/lodepng_util.cpp +++ b/lodepng_util.cpp @@ -198,8 +198,7 @@ unsigned getFilterTypesInterlaced(std::vector<std::vector<unsigned char> >& filt for(size_t j = 0; j < 7; j++) { unsigned w2 = (w - ADAM7_IX[j] + ADAM7_DX[j] - 1) / ADAM7_DX[j]; unsigned h2 = (h - ADAM7_IY[j] + ADAM7_DY[j] - 1) / ADAM7_DY[j]; - if(ADAM7_IX[j] >= w) w2 = 0; - if(ADAM7_IY[j] >= h) h2 = 0; + if(ADAM7_IX[j] >= w || ADAM7_IY[j] >= h) continue; size_t linebytes = 1 + lodepng_get_raw_size(w2, 1, &state.info_png.color); for(size_t i = 0; i < h2; i++) { filterTypes[j].push_back(data[pos]); @@ -219,17 +218,24 @@ unsigned getFilterTypes(std::vector<unsigned char>& filterTypes, const std::vect if(passes.size() == 1) { filterTypes.swap(passes[0]); } else { + // Simplify interlaced filter types to get a single filter value per scanline: + // put pass 6 and 7 alternating in the one vector, these filters + // correspond to the closest to what it would be for non-interlaced + // image. If the image is only 1 pixel wide, pass 6 doesn't exist so the + // alternative values column0 are used. The shift values are to match + // the y position in the interlaced sub-images. + // NOTE: the values 0-6 match Adam7's passes 1-7. + const unsigned column0[8] = {0, 6, 4, 6, 2, 6, 4, 6}; + const unsigned column1[8] = {5, 6, 5, 6, 5, 6, 5, 6}; + const unsigned shift0[8] = {3, 1, 2, 1, 3, 1, 2, 1}; + const unsigned shift1[8] = {1, 1, 1, 1, 1, 1, 1, 1}; lodepng::State state; unsigned w, h; lodepng_inspect(&w, &h, &state, &png[0], png.size()); - /* - Interlaced. Simplify it: put pass 6 and 7 alternating in the one vector so - that one filter per scanline of the uninterlaced image is given, with that - filter corresponding the closest to what it would be for non-interlaced - image. - */ + const unsigned* column = w > 1 ? column1 : column0; + const unsigned* shift = w > 1 ? shift1 : shift0; for(size_t i = 0; i < h; i++) { - filterTypes.push_back(i % 2 == 0 ? passes[5][i / 2] : passes[6][i / 2]); + filterTypes.push_back(passes[column[i & 7u]][i >> shift[i & 7u]]); } } return 0; /* OK */ |