Source

gd-libgd / src / testac.c

#include <stdio.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[])
{
	/* Input and output files */
	FILE *in;
	FILE *out;

	/* Input image */
	gdImagePtr im_in = 0;

	/* Colors */
	int lightBlue;

	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);
	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);
	}

	gdImagePng(im_out, out);
	fclose(out);

	gdImageDestroy(im_out);
}