png.c

htp是一个HTML预处理器。页面可以用htp扩展的类HTML的宏编写。这可以简化维护一个一致外观的Web页面集.

/*
//
// png.c
//
// PNG (Portable Network Graphic format) support functions
//
// Copyright (c) 2001 Kentarou Fukuchi.  Permission to distribute
// granted by the author.  No warranties are made on the fitness of this
// source code.
//
*/

#include "htp.h"

BOOL PngFormatFound(FILE *file)
{
    BYTE header[8];
	BYTE png_sig[8] = {137, 80, 78, 71, 13, 10, 26, 10};

    /* move to BOF */
    if(fseek(file, 0, SEEK_SET) != 0)
    {
        DEBUG_PRINT(("unable to seek to start of PNG file"));
        return FALSE;
    }

    /* read first eight bytes, looking for PNG header */
    if(fread(header, 1, 8, file) != 8)
    {
        DEBUG_PRINT(("could not read PNG image file header"));
        return FALSE;
    }

    /* is this a PNG file? */
    if(memcmp(header, png_sig, 8) == 0)
    {
        return TRUE;
    }

    /* not a PNG file */
    return FALSE;
}

BOOL PngReadDimensions(FILE *file, WORD *height, WORD *width)
{
	unsigned int length;
	unsigned char buf[4];

    /* move to the image size position in the file header */
    if(fseek(file, 8, SEEK_SET) != 0)
    {
        DEBUG_PRINT(("unable to seek to start of PNG file"));
        return FALSE;
    }

	for(;;)
	{
		/* read the length of chunk */
		if(fread(&length, 1, 4, file) != 4)
		{
			return FALSE;
		}
		/* read the chunk name */
		if(fread(&buf, 1, 4, file) != 4)
		{
			return FALSE;
		}
		if(memcmp(buf, "IHDR", 4) != 0)
		{
			if(fseek(file, length, SEEK_CUR) != 0)
			{
				return FALSE;
			}
			continue;
		} else {
			if(fread(&buf, 1, 4, file) != 4)
			{
				return FALSE;
			}
			*width = MAKE_WORD(buf[2], buf[3]);
			if(fread(&buf, 1, 4, file) != 4)
			{
				return FALSE;
			}
			*height = MAKE_WORD(buf[2], buf[3]);
			break;
		}
	}

    return TRUE;
}