bmp2png---using libpng

#include <png.h> #include <stdio.h> #include <stdlib.h> #include <stdint.h> /* A coloured pixel. */ typedef struct { uint8_t red; uint8_t green; uint8_t blue; } pixel_t; /* A picture. */ typedef struct { pixel_t *pixels; size_t width; size_t height; } bitmap_t; /* Given "bitmap", this returns the pixel of bitmap at the point ("x", "y"). */ static pixel_t * pixel_at (bitmap_t * bitmap, int x, int y) { return bitmap->pixels + bitmap->width * y + x; } /* Write "bitmap" to a PNG file specified by "path"; returns 0 on success, non-zero on error. */ static int save_png_to_file (bitmap_t *bitmap, const char *path) { FILE * fp; png_structp png_ptr = NULL; png_infop info_ptr = NULL; size_t x, y; png_byte ** row_pointers = NULL; /* "status" contains the return value of this function. At first it is set to a value which means 'failure'. When the routine has finished its work, it is set to a value which means 'success'. */ int status = -1; /* The following number is set by trial and error only. I cannot see where it it is documented in the libpng manual. */ int pixel_size = 3; int depth = 8; fp = fopen (path, "wb"); if (! fp) { goto fopen_failed; } png_ptr = png_create_write_struct (PNG_LIBPNG_VER_STRING, NULL, NULL, NULL); if (png_ptr == NULL) { goto png_create_write_struct_failed; } info_ptr = png_create_info_struct (png_ptr); if (info_ptr == NULL) { goto png_create_info_struct_failed; } /* Set up error handling. */ if (setjmp (png_jmpbuf (png_ptr))) { goto png_failure; } /* Set image attributes. */ png_set_IHDR (png_ptr, info_ptr, bitmap->width, bitmap->height, depth, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT); /* Initialize rows of PNG. */ row_pointers = png_malloc (png_ptr, bitmap->height * sizeof (png_byte *)); for (y = 0; y < bitmap->height; ++y) { png_byte *row = png_malloc (png_ptr, sizeof (uint8_t) * bitmap->width * pixel_size); row_pointers[y] = row; for (x = 0; x < bitmap->width; ++x) { pixel_t * pixel = pixel_at (bitmap, x, y); *row++ = pixel->red; *row++ = pixel->green; *row++ = pixel->blue; } } /* Write the image data to "fp". */ png_init_io (png_ptr, fp); png_set_rows (png_ptr, info_ptr, row_pointers); png_write_png (png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL); /* The routine has successfully written the file, so we set "status" to a value which indicates success. */ status = 0; for (y = 0; y < bitmap->height; y++) { png_free (png_ptr, row_pointers[y]); } png_free (png_ptr, row_pointers); png_failure: png_create_info_struct_failed: png_destroy_write_struct (&png_ptr, &info_ptr); png_create_write_struct_failed: fclose (fp); fopen_failed: return status; } /* Given "value" and "max", the maximum value which we expect "value" to take, this returns an integer between 0 and 255 proportional to "value" divided by "max". */ static int pix (int value, int max) { if (value < 0) return 0; return (int) (256.0 *((double) (value)/(double) max)); } int main () { bitmap_t fruit; int x; int y; /* Create an image. */ fruit.width = 100; fruit.height = 100; fruit.pixels = calloc (sizeof (pixel_t), fruit.width * fruit.height); for (y = 0; y < fruit.height; y++) { for (x = 0; x < fruit.width; x++) { pixel_t * pixel = pixel_at (& fruit, x, y); pixel->red = pix (x, fruit.width); pixel->green = pix (y, fruit.height); } } /* Write the image to a file 'fruit.png'. */ save_png_to_file (& fruit, "fruit.png"); return 0; }