Source

gd-libgd / src / testac.c


#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdio.h>
#include <stdlib.h>
#include "gd.h"

/* If palette is true, we convert from truecolor to palette at the end,
   to test gdImageTrueColorToPalette and see file size/
   quality tradeoffs. */

void testDrawing (gdImagePtr im_in,
		  double scale, int blending, int palette, char *filename);

int
main (int argc, char *argv[])
{
#ifdef HAVE_LIBPNG
	/* Input and output files */
	FILE *in;

	/* Input image */
	gdImagePtr im_in = 0;

	if (argc != 2) {
		fprintf (stderr, "Usage: testac filename.png\n");
		exit (1);
	}
	/* Load original PNG, which should contain alpha channel
	   information. We will use it in two ways: preserving it
	   literally, for use with compatible browsers, and
	   compositing it ourselves against a background of our
	   choosing (alpha blending). We'll change its size
	   and try creating palette versions of it. */
	in = fopen (argv[1], "rb");
	if (!in) {
		fprintf (stderr, "Can't load %s.\n", argv[1]);
		exit (1);
	} else {
		im_in = gdImageCreateFromPng (in);
		fclose (in);
	}
	testDrawing (im_in, 1.0, 0, 0, "noblending-fullsize-truecolor.png");
	testDrawing (im_in, 1.0, 1, 0, "blending-fullsize-truecolor.png");
	testDrawing (im_in, 0.5, 0, 0, "noblending-halfsize-truecolor.png");
	testDrawing (im_in, 0.5, 1, 0, "blending-halfsize-truecolor.png");
	testDrawing (im_in, 2.0, 0, 0, "noblending-doublesize-truecolor.png");
	testDrawing (im_in, 2.0, 1, 0, "blending-doublesize-truecolor.png");
	testDrawing (im_in, 1.0, 0, 1, "noblending-fullsize-palette.png");
	testDrawing (im_in, 1.0, 1, 1, "blending-fullsize-palette.png");
	testDrawing (im_in, 0.5, 0, 1, "noblending-halfsize-palette.png");
	testDrawing (im_in, 0.5, 1, 1, "blending-halfsize-palette.png");
	testDrawing (im_in, 2.0, 0, 1, "noblending-doublesize-palette.png");
	testDrawing (im_in, 2.0, 1, 1, "blending-doublesize-palette.png");
	gdImageDestroy (im_in);
#else
	fprintf (stderr, "No PNG library support.\n");
#endif

	return 0;
}

/* If palette is true, we convert from truecolor to palette at the end,
   to test gdImageTrueColorToPalette and see file size/
   quality tradeoffs. */
void
testDrawing (gdImagePtr im_in,
	     double scale, int blending, int palette, char *filename)
{
	gdImagePtr im_out;
	FILE *out;
	/* Create output image. */
	im_out = gdImageCreateTrueColor ((int) (gdImageSX (im_in) * scale),
					 (int) (gdImageSY (im_in) * scale));
	/*
	   Request alpha blending. This causes future
	   drawing operations to perform alpha channel blending
	   with the background, resulting in an opaque image.
	   Without this call, pixels in the foreground color are
	   copied literally, *including* the alpha channel value,
	   resulting in an output image which is potentially
	   not opaque. This flag can be set and cleared as often
	   as desired. */
	gdImageAlphaBlending (im_out, blending);

	/* Flood with light blue. */
	gdImageFill (im_out, (int) (gdImageSX (im_in) * scale / 2),
		     (int) (gdImageSY (im_in) * scale / 2),
		     gdTrueColor (192, 192, 255));
	/* Copy the source image. Alpha blending should result in
	   compositing against red. With blending turned off, the
	   browser or viewer will composite against its preferred
	   background, or, if it does not support an alpha channel,
	   we will see the original colors for the pixels that
	   ought to be transparent or semitransparent. */
	gdImageCopyResampled (im_out, im_in,
			      0, 0,
			      0, 0,
			      (int) (gdImageSX (im_in) * scale),
			      (int) (gdImageSY (im_in) * scale), gdImageSX (im_in),
			      gdImageSY (im_in));
	/* Write PNG */
	out = fopen (filename, "wb");

	/* If this image is the result of alpha channel blending,
	   it will not contain an interesting alpha channel itself.
	   Save a little file size by not saving the alpha channel.
	   Otherwise the file would typically be slightly larger. */
	gdImageSaveAlpha (im_out, !blending);

	/* If requested, convert from truecolor to palette. */
	if (palette) {
		/* Dithering, 256 colors. */
		gdImageTrueColorToPalette (im_out, 1, 256);
	}

#ifdef HAVE_LIBPNG
	gdImagePng (im_out, out);
#else
	fprintf (stderr, "No PNG library support.\n");
#endif
	fclose (out);

	gdImageDestroy (im_out);
}