diff options
Diffstat (limited to 'libdimension-png/png.c')
| -rw-r--r-- | libdimension-png/png.c | 53 |
1 files changed, 46 insertions, 7 deletions
diff --git a/libdimension-png/png.c b/libdimension-png/png.c index b639900..7e9036f 100644 --- a/libdimension-png/png.c +++ b/libdimension-png/png.c @@ -24,6 +24,8 @@ #include <arpa/inet.h> #include <stdlib.h> +/* Write a canvas to a png file, using libpng. Return 0 on success, nonzero on + failure. */ int dmnsn_png_write_canvas(const dmnsn_canvas *canvas, FILE *file) { @@ -35,54 +37,65 @@ dmnsn_png_write_canvas(const dmnsn_canvas *canvas, FILE *file) dmnsn_color color; dmnsn_sRGB sRGB; + if (!file) return 1; /* file was NULL */ + width = canvas->x; height = canvas->y; - if (!file) return 1; - png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL); - if (!png_ptr) return 1; + if (!png_ptr) return 1; /* Couldn't create libpng write struct */ info_ptr = png_create_info_struct(png_ptr); if (!info_ptr) { + /* Couldn't create libpng info struct */ png_destroy_write_struct(&png_ptr, NULL); return 1; } + /* libpng will longjmp here if it encounters an error from here on */ if (setjmp(png_jmpbuf(png_ptr))) { + /* libpng error */ if (row) free(row); png_destroy_write_struct(&png_ptr, &info_ptr); return 1; } + /* Associate file with the libpng write struct */ png_init_io(png_ptr, file); + /* Set header correctly for 16-bit sRGB image */ png_set_IHDR(png_ptr, info_ptr, width, height, 16, PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT); - png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr, PNG_sRGB_INTENT_ABSOLUTE); + /* We think of transparency in the opposite way that PNG does */ png_set_invert_alpha(png_ptr); + + /* Write the info struct */ png_write_info(png_ptr, info_ptr); if (htonl(1) != 1) { - /* We are little-endian */ + /* We are little-endian; swap the byte order of the pixels */ png_set_swap(png_ptr); } + /* Allocate the temporary row of RGBA values */ row = malloc(4*sizeof(uint16_t)*width); if (!row) { png_destroy_write_struct(&png_ptr, &info_ptr); return 1; } + /* Write the pixels */ for (y = 0; y < height; ++y) { for (x = 0; x < width; ++x) { /* Invert the rows. PNG coordinates are fourth quadrant. */ color = dmnsn_get_pixel(canvas, x, height - y - 1); sRGB = dmnsn_sRGB_from_color(color); + /* Saturate R, G, and B to [0, UINT16_MAX] */ + if (sRGB.R <= 0.0) { row[4*x] = 0; } else if (sRGB.R >= 1.0) { @@ -107,11 +120,15 @@ dmnsn_png_write_canvas(const dmnsn_canvas *canvas, FILE *file) row[4*x + 2] = sRGB.B*UINT16_MAX; } + /* color.filter + color.trans is in [0.0, 1.0] by definition */ row[4*x + 3] = (color.filter + color.trans)*UINT16_MAX; } + + /* Write the row */ png_write_row(png_ptr, (png_bytep)row); } + /* Finish the PNG file */ png_write_end(png_ptr, info_ptr); free(row); @@ -119,6 +136,7 @@ dmnsn_png_write_canvas(const dmnsn_canvas *canvas, FILE *file) return 0; } +/* Read a canvas from the PNG file `file'. Return NULL on error. */ dmnsn_canvas * dmnsn_png_read_canvas(FILE *file) { @@ -135,32 +153,40 @@ dmnsn_png_read_canvas(FILE *file) dmnsn_sRGB sRGB; png_bytep png_pixel; - if (!file) return NULL; + if (!file) return NULL; /* file was NULL */ fread(header, 1, 8, file); - if (png_sig_cmp(header, 0, 8)) return NULL; + if (png_sig_cmp(header, 0, 8)) return NULL; /* file is not a PNG file */ + /* Create the libpng read struct */ png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL); if (!png_ptr) return NULL; + /* Create the libpng info struct */ info_ptr = png_create_info_struct(png_ptr); if (!info_ptr) { png_destroy_read_struct(&png_ptr, NULL, NULL); return NULL; } + /* libpng will longjmp here if it encounters an error from here on */ if (setjmp(png_jmpbuf(png_ptr))) { + /* libpng error */ if (row_pointers) free(row_pointers); if (image) free(image); png_destroy_read_struct(&png_ptr, &info_ptr, NULL); return NULL; } + /* Associate the read struct with the file, and tell it we've already checked + 8 bytes of signature */ png_init_io(png_ptr, file); png_set_sig_bytes(png_ptr, 8); + /* Read the PNG header into info struct */ png_read_info(png_ptr, info_ptr); + /* Get useful information from the info struct */ png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type, &interlace_type, &compression_type, &filter_method); @@ -182,15 +208,21 @@ dmnsn_png_read_canvas(FILE *file) } png_set_invert_alpha(png_ptr); + /* Update the info struct */ png_read_update_info(png_ptr, info_ptr); + + /* Get bytes/image row */ rowbytes = png_get_rowbytes(png_ptr, info_ptr); + /* Allocate the temporary image buffer */ image = malloc(rowbytes*height); if (!image) { png_destroy_read_struct(&png_ptr, &info_ptr, NULL); return NULL; } + /* Allocate and set an array of pointers to rows in image */ + row_pointers = malloc(sizeof(png_bytep)*height); if (!row_pointers) { free(image); @@ -202,8 +234,11 @@ dmnsn_png_read_canvas(FILE *file) row_pointers[y] = image + y*rowbytes; } + /* Read the image to image all at once. At the expense of greater memory use, + this handles interlacing for us. */ png_read_image(png_ptr, row_pointers); + /* Allocate the canvas */ canvas = dmnsn_new_canvas(width, height); if (!canvas) { free(row_pointers); @@ -213,6 +248,10 @@ dmnsn_png_read_canvas(FILE *file) return NULL; } + /* Now we convert the image to our canvas format. This depends on the image + bit depth (which has been scaled up to at least 8 or 16), and the presence + of an alpha channel. For performance reasons, the tests are outside the + loops, although that doesn't really matter for a decent compiler. */ if (bit_depth == 16) { if (color_type & PNG_COLOR_MASK_ALPHA) { for (x = 0; x < width; ++x) { |