/* tga.c : PUBLIC DOMAIN - Jon Mayo - August 24, 2006
 * - You may remove any comments you wish, modify this code any way you wish,
 *   and distribute any way you wish.*/
/* simple TGA save program. supports 8-bit color and grayscale
 * define STAND_ALONE to run the example routine */
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>

/* WRite Little-Endian 16-bit value */
#define WR_LE16BIT(dest, offset, value) do { \
		unsigned tmp=value; \
		(dest)[offset]=tmp%256; \
		(dest)[offset+1]=(tmp/256)%256; \
	} while(0)

/* saves an image to a TGA file.
 * palette points to an array of RGB values (with a pad on each entry) 
 * pass palette as NULL to use a grayscale palette
 * nr_colors must be large enough for all pixels that were passed.
 */
static int tga_save(const char *filename, unsigned char *data, unsigned width, unsigned height, unsigned char palette[][4], unsigned nr_colors ) {
	unsigned y, c;
	FILE *f;
	unsigned char header[] = {
		0,		/* 00 - length of image identification field */
		1,		/* 01 - color map type */
		1,		/* 02 - image type code */
		/* color map specification */	
		0, 0,		/* 03 - color map origin */
		0, 1, 		/* 05 - color map length */
		24,		/* 07 - color map entry size (24-bit) */
		/* image specification */
		0, 0,		/* 08 - X origin */
		0, 0,		/* 10 - Y origin */
		0, 0,		/* 12 - width */
		0, 0,		/* 14 - height */
		8,		/* 16 - image pixel size */
		0,		/* 17 - image description byte */
		/* image identification field */
		0,		/* 18 - empty */
	};
	
	assert(filename != NULL);
	assert(nr_colors > 0);
	assert(data != NULL);
	assert(width > 0 && height > 0);

	f=fopen(filename, "wb");
	if(!f) {
		perror(filename);
		return 0;
	}

	WR_LE16BIT(header, 12, width);
	WR_LE16BIT(header, 14, height);
	WR_LE16BIT(header, 5, nr_colors);
	/* TODO: support smaller pixel size for reduced colors */

	/* write header */
	if(fwrite(header, sizeof header, 1, f)!=1) {
		perror(filename);
		fclose(f);
		return 0;
	}

	/* color map data */
	if(palette) {
		/* write the palette */
		for(c=0;c<nr_colors;c++) {
			if(fwrite(palette[c], 3, 1, f)!=1) {
				perror(filename);
				fclose(f);
				return 0;
			}
		}
	} else {
		unsigned char pal[3];
		/* construct a grayscale palette */
		for(c=0;c<nr_colors;c++) {
			pal[0]=c;
			pal[1]=c;
			pal[2]=c;
			if(fwrite(pal, sizeof pal, 1, f)!=1) {
				perror(filename);
				fclose(f);
				return 0;
			}
		}
	}
	/* image data field */
	for(y=0;y<height;y++) {
		if(fwrite(data+y*width, width, 1, f)!=1) {
			perror(filename);
			fclose(f);
			return 0;
		}
	}
	fclose(f);
	fprintf(stderr, "Wrote TARGA '%s' %ux%u\n", filename, width, height);

	return 1;
}

#ifdef STAND_ALONE
/* example that makes a simple TGA. */
#define NR(x) (sizeof(x)/sizeof*(x))
int main(int argc, char **argv) {
	unsigned width=256, height=256;
	unsigned char *data;
	unsigned x,y;
	unsigned char palette[256][4];

	/* read in the width and height parameters */
	if(argc>1) {
		switch(argc) {
			case 3:
				height=strtoul(argv[2], 0, 0);
			case 2:
				width=strtoul(argv[1], 0, 0);
				break;
			default:
				fprintf(stderr, "Usage: %s [width [height [colors]]]\n", argv[0]);
				return EXIT_FAILURE;
		}
	}

	/* buffer for our grayscale image */
	data=malloc(width * height);

	for(y=0;y<256;y++) {
		palette[y][0]=y;
		palette[y][1]=255-y;
		palette[y][2]=~y;
		palette[y][3]=0; /* pad */
	}

	/* fill in data with something intersting */
	for(y=0;y<height;y++) 
		for(x=0;x<width;x++) 
			data[y*width+x]=255-((x-128)*(x-128) + (y-128)*(y-128))/128;

	/* save the image */
	if(!tga_save("test.tga", data, width, height, palette, 256)) {
		fprintf(stderr, "FAILED!\n");
		return EXIT_FAILURE;
	}
	free(data);
	return 0;
}
#endif