William Osler
7 years ago
6 changed files with 166 additions and 4 deletions
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#include <stdlib.h> |
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#include <inttypes.h> |
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#include <string.h> |
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#include <stdbool.h> |
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#include <stdio.h> |
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#include <err.h> |
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#include <errno.h> |
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#include <cairo.h> |
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#include <jpeglib.h> |
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#include "jpg.h" |
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/*
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* Checks if the file is a JPEG by looking for a valid JPEG header. |
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*/ |
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bool file_is_jpg(char* file_path) { |
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FILE* image_file; |
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uint16_t file_header; |
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size_t read_count; |
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// TODO: Consider endianess on non-x86 platforms
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uint16_t jpg_magick = 0xd8ff; |
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image_file = fopen(file_path, "rb"); |
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if (image_file == NULL) { |
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int img_err = errno; |
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fprintf(stderr, "Could not open image file %s: %s\n", |
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file_path, strerror(img_err)); |
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return false; |
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} |
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read_count = fread(&file_header, sizeof(file_header), 1, image_file); |
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fclose(image_file); |
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if (read_count < 1) { |
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fprintf(stderr, "Error searching for JPEG header in %s\n", file_path); |
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return false; |
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} |
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return file_header == jpg_magick; |
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} |
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/*
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* Reads a JPEG from a file into memory, in a format that Cairo can create a |
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* surface from. |
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*/ |
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void* read_JPEG_file(char *file_path, JPEG_INFO *jpg_info) { |
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int img_err; |
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struct jpeg_decompress_struct cinfo; |
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struct jpeg_error_mgr jerr; |
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FILE *infile; /* source file */ |
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void *img; /* decompressed image data pointer */ |
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if ((infile = fopen(file_path, "rb")) == NULL) { |
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img_err = errno; |
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fprintf(stderr, "Could not open image file %s: %s\n", |
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file_path, strerror(img_err)); |
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return NULL; |
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} |
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cinfo.err = jpeg_std_error(&jerr); |
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jpeg_create_decompress(&cinfo); |
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jpeg_stdio_src(&cinfo, infile); |
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(void) jpeg_read_header(&cinfo, TRUE); |
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// BGRA + endianness change = RGBA?
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// TODO: Test this code on non-x86_64 platforms
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cinfo.out_color_space = JCS_EXT_BGRA; |
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(void) jpeg_start_decompress(&cinfo); |
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jpg_info->height = cinfo.output_height; |
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jpg_info->width = cinfo.output_width; |
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/* Get the *cairo* stride rather than the stride from the image. This is
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* the space needed in memory for each row for optimized Cairo rendering. */ |
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int cairo_stride = cairo_format_stride_for_width(CAIRO_FORMAT_ARGB32, |
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cinfo.output_width); |
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jpg_info->stride = cairo_stride; |
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if (cairo_stride < jpg_info->width) { |
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/* This should never happen, but if it does then the following code
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* will potentially write into unallocated memory */ |
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fprintf( |
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stderr, |
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"WARNING: Cairo stride shorter than JPEG width. Aborting JPEG read." |
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); |
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return NULL; |
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} |
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// Allocate storage for the final, decompressed image.
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img = calloc(cairo_stride, cinfo.output_height); |
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if (img == NULL) { |
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fprintf(stderr, "Could not allocate memory for JPEG decode\n"); |
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(void) jpeg_finish_decompress(&cinfo); |
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jpeg_destroy_decompress(&cinfo); |
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fclose(infile); |
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return NULL; |
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} |
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while (cinfo.output_scanline < cinfo.output_height) { |
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/* Normally, you would allocate a buffer using libJPEG's memory
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* management and write into it, but since we're reading one row at a |
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* time, we just write it directly into the image memory space */ |
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unsigned char* pos = img + (cairo_stride * (cinfo.output_scanline)); |
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(void) jpeg_read_scanlines(&cinfo, &pos, 1); |
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} |
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(void) jpeg_finish_decompress(&cinfo); |
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jpeg_destroy_decompress(&cinfo); |
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fclose(infile); |
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return img; |
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} |
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@ -0,0 +1,21 @@ |
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#ifndef _JPG_H |
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#define _JPG_H |
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typedef struct { |
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uint height; |
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uint width; |
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uint stride; // The width of each row in memory, in bytes
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} JPEG_INFO; |
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/*
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* Checks if the file is a JPEG by looking for a valid JPEG header. |
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*/ |
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bool file_is_jpg(char* file_path); |
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|
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/*
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* Reads a JPEG from a file into memory, in a format that Cairo can create a |
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* surface from. |
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*/ |
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void* read_JPEG_file(char *filename, JPEG_INFO *jpg_info); |
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#endif |
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