watermark an image with the vips8 C API

watermark.c

/* watermark an image with libvips C. It handles monon, RGB and CMYK images.
 *
 * compile with

 	gcc -g -Wall watermark.c `pkg-config vips --cflags --libs`

 */

#include <vips/vips.h>

int
main( int argc, char **argv )
{
	/* The colour we paint the text with. We need different colours for
	 * monoo, RGB and CMYK.
	 */
	double colour_mono[1] = { 1.0 };
	double colour_rgb[3] = { 1.0, 0.0, 0.0 };
	double colour_cmyk[4] = { 0.0, 1.0, 0.0, 0.5 };
	double zeros[4] = { 0.0, };

	VipsImage *base;
	VipsImage **t;
	VipsImage *in;
	const double *colour;
	int overlay_bands;
	VipsImage *overlay;

	if( VIPS_INIT( argv[0] ) )
		vips_error_exit( NULL );

	if( argc != 4 ) 
		vips_error_exit( "usage: %s in-file out-file \"message\"", 
			argv[0] ); 

	base = vips_image_new();
	t = (VipsImage **) vips_object_local_array( VIPS_OBJECT( base ), 12 );

	if( !(t[0] = vips_image_new_from_file( argv[1], 
		"access", VIPS_ACCESS_SEQUENTIAL,
		NULL )) ) {
		g_object_unref( base );
		vips_error_exit( NULL );
	}
	in = t[0];

	/* Make the mask. We pick a text colour that matches the image type.
	 */
	switch( in->Type ) {
	case VIPS_INTERPRETATION_B_W:
		colour = colour_mono;
		overlay_bands = 1;
		break;

	case VIPS_INTERPRETATION_sRGB:
		colour = colour_rgb;
		overlay_bands = 3;
		break;

	case VIPS_INTERPRETATION_CMYK:
		colour = colour_cmyk;
		overlay_bands = 4;
		break;

	default:
		vips_error_exit( "unsupported image interpretation" );
	}

	if( vips_text( &t[1], argv[3],
			"width", 500,
			"dpi", 300,
			NULL ) ||
		vips_linear( t[1], &t[2], 
			colour, zeros, overlay_bands, NULL ) ||
		vips_linear1( t[1], &t[3], 0.3, 0, NULL ) ||
		vips_bandjoin2( t[2], t[3], &t[4], NULL ) ||
		vips_cast( t[4], &t[5], VIPS_FORMAT_UCHAR, NULL ) ||
		vips_copy( t[5], &t[6], 
			"interpretation", in->Type,
			NULL ) || 
		vips_embed( t[6], &t[7], 100, 100, 
			t[6]->Xsize + 200, t[6]->Ysize + 200, NULL ) ||
		vips_replicate( t[7], &t[8], 
			1 + in->Xsize / t[7]->Xsize, 
			1 + in->Ysize / t[7]->Ysize, NULL ) ||
		vips_crop( t[8], &t[9], 0, 0, 
			in->Xsize, in->Ysize, NULL ) ) {
		g_object_unref( base );
		vips_error_exit( NULL );
	}
	overlay = t[9];

	/* Blend the image and overlay and write to output.
	 */
	if( vips_composite2( in, overlay, &t[10], 
			VIPS_BLEND_MODE_OVER, NULL ) ||
		vips_image_write_to_file( t[10], argv[2], NULL ) ) { 
		g_object_unref( base );
		vips_error_exit( NULL );
	}

	g_object_unref( base );

	return( 0 );
}