[libpng16] Added contrib/examples/simpleover.c, to demonstrate how to handle
alpha compositing of multiple images, using the "simplified API"
This commit is contained in:
John Bowler
Glenn Randers-Pehrson
parent
216ab04994
commit
cde3078963
7
ANNOUNCE
7
ANNOUNCE
@ -1,4 +1,4 @@
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Libpng 1.6.18beta03 - April 29, 2015
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Libpng 1.6.18beta03 - May 3, 2015
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This is not intended to be a public release. It will be replaced
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within a few weeks by a public version or by another test version.
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@ -38,9 +38,12 @@ Version 1.6.18beta02 [April 26, 2015]
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Suppressed some warnings from the Borland C++ 5.5.1/5.82 compiler
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(Bug report by Viktor Szaka'ts).
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Version 1.6.18beta03 [April 29, 2015]
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Version 1.6.18beta03 [May 3, 2015]
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Replaced "unexpected" with an integer (0xabadca11) in pngset.c
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where a long was expected, to avoid a compiler warning when PNG_DEBUG > 1.
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Added contrib/examples/simpleover.c, to demonstrate how to handle
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alpha compositing of multiple images, using the "simplified API"
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(John Bowler).
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Send comments/corrections/commendations to png-mng-implement at lists.sf.net
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(subscription required; visit
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5
CHANGES
5
CHANGES
@ -5218,9 +5218,12 @@ Version 1.6.18beta02 [April 26, 2015]
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Suppressed some warnings from the Borland C++ 5.5.1/5.82 compiler
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(Bug report by Viktor Szaka'ts).
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Version 1.6.18beta03 [April 29, 2015]
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Version 1.6.18beta03 [May 3, 2015]
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Replaced "unexpected" with an integer (0xabadca11) in pngset.c
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where a long was expected, to avoid a compiler warning when PNG_DEBUG > 1.
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Added contrib/examples/simpleover.c, to demonstrate how to handle
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alpha compositing of multiple images, using the "simplified API"
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(John Bowler).
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Send comments/corrections/commendations to png-mng-implement at lists.sf.net
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||||
(subscription required; visit
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642
contrib/examples/simpleover.c
Normal file
642
contrib/examples/simpleover.c
Normal file
@ -0,0 +1,642 @@
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/*- simpleover
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*
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* COPYRIGHT: Written by John Cunningham Bowler, 2015.
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* To the extent possible under law, the author has waived all copyright and
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* related or neighboring rights to this work. This work is published from:
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* United States.
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*
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* Read several PNG files, which should have an alpha channel or transparency
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* information, and composite them together to produce one or more 16-bit linear
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* RGBA intermediates. This involves doing the correct 'over' composition to
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* combine the alpha channels and corresponding data.
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*
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* Finally read an output (background) PNG using the 24-bit RGB format (the
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* PNG will be composited on green (0x00ff00) by default if it has an alpha
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* channel) and apply the intermediate image generated above to specified
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* locations in the image.
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*
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* The command line has the general format:
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*
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* simpleover <background.png> [output.png]
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* {--sprite=width,height,name {[--at=x,y] {sprite.png}}}
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* {--add=name {x,y}}
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*
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* The --sprite and --add options may occur multiple times, they are executed
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* in order. --add may refer to any sprite already read.
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*
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* This code is intended to show how to composite multiple images together
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* correctly. Apart from the libpng Simplified API the only work done in here
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* is to combine multiple input PNG images into a single sprite; this involves
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* a Porter-Duff 'over' operation and the input PNG images may, as a result,
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* be regarded as being layered one on top of the other with the first (leftmost
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* on the command line) being at the bottom and the last on the top.
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*/
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#include <stddef.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdio.h>
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#include <errno.h>
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/* Normally use <png.h> here to get the installed libpng, but this is done to
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* ensure the code picks up the local libpng implementation, so long as this
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* file is linked against a sufficiently recent libpng (1.6+) it is ok to
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* change this to <png.h>:
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*/
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#include "../../png.h"
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#define sprite_name_chars 15
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struct sprite {
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FILE *file;
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png_uint_16p buffer;
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unsigned int width;
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unsigned int height;
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char name[sprite_name_chars+1];
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};
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#if 0 /* div by 65535 test program */
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#include <math.h>
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#include <stdio.h>
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int main(void) {
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double err = 0;
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unsigned int xerr = 0;
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unsigned int r = 32768;
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{
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unsigned int x = 0;
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do {
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unsigned int t = x + (x >> 16) + (x >> 31) + r;
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double v = x, errtest;
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if (t < x) {
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fprintf(stderr, "overflow: %u+%u -> %u\n", x, r, t);
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return 1;
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}
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v /= 65535;
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errtest = v;
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t >>= 16;
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errtest -= t;
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if (errtest > err) {
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err = errtest;
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xerr = x;
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if (errtest >= .5) {
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fprintf(stderr, "error: %u/65535 = %f, not %u, error %f\n",
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x, v, t, errtest);
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return 0;
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}
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}
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} while (++x <= 65535U*65535U);
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}
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printf("error %f @ %u\n", err, xerr);
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return 0;
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}
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#endif /* div by 65535 test program */
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static void
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sprite_op(const struct sprite *sprite, int x_offset, int y_offset,
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png_imagep image, const png_uint_16 *buffer)
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{
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/* This is where the Porter-Duff 'Over' operator is evaluated; change this
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* code to change the operator (this could be parameterized). Any other
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* image processing operation could be used here.
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*/
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/* Check for an x or y offset that pushes the image beyond the right or
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* bottom of the sprite:
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*/
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if ((y_offset < 0 || (unsigned)/*SAFE*/y_offset < sprite->height) &&
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(x_offset < 0 || (unsigned)/*SAFE*/x_offset < sprite->width))
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{
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unsigned int y = 0;
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if (y_offset < 0)
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y = -y_offset; /* Skip to first visible row */
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do
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{
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unsigned int x = 0;
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if (x_offset < 0)
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x = -x_offset;
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do
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{
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/* In and out are RGBA values, so: */
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const png_uint_16 *in_pixel = buffer + (y * image->width + x)*4;
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png_uint_32 in_alpha = in_pixel[3];
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/* This is the optimized Porter-Duff 'Over' operation, when the
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* input alpha is 0 the output is not changed.
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*/
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if (in_alpha > 0)
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{
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png_uint_16 *out_pixel = sprite->buffer +
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((y+y_offset) * sprite->width + (x+x_offset))*4;
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/* This is the weight to apply to the output: */
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in_alpha = 65535-in_alpha;
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if (in_alpha > 0)
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{
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/* The input must be composed onto the output. This means
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* multiplying the current output pixel value by the inverse
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* of the input alpha (1-alpha). A division is required but
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* it is by the constant 65535. Approximate this as:
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*
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* (x + (x >> 16) + (x >> 31) + 32768) >> 16;
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*
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* This is exact (and does not overflow) for all values of
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* x in the range 0..65535*65535. (Note that the calculation
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* produces the closest integer, the maximum error is <0.5).
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*/
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png_uint_32 tmp;
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# define compose(c)\
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tmp = out_pixel[c] * in_alpha;\
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tmp = (tmp + (tmp >> 16) + (tmp >> 31) + 32768) >> 16;\
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out_pixel[c] = tmp + in_pixel[c]
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/* The following is very vectorizable... */
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compose(0);
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compose(1);
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compose(2);
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compose(3);
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}
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else
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out_pixel[0] = in_pixel[0],
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out_pixel[1] = in_pixel[1],
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out_pixel[2] = in_pixel[2],
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out_pixel[3] = in_pixel[3];
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}
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}
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while (++x < image->width);
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}
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while (++y < image->height);
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}
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}
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static int
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create_sprite(struct sprite *sprite, int *argc, const char ***argv)
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{
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/* Read the arguments and create this sprite, the sprite buffer has already
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* been allocated. This reads the input PNGs one by one in linear format,
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* composes them onto the sprite buffer (the code in the function above)
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* then saves the result, converting it on the fly to PNG RGBA 8-bit format.
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*/
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while (*argc > 0)
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{
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char tombstone;
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int x = 0, y = 0;
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if ((*argv)[0][0] == '-' && (*argv)[0][1] == '-')
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{
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/* The only supported option is --at. */
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if (sscanf((*argv)[0], "--at=%d,%d%c", &x, &y, &tombstone) != 2)
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break; /* success; caller will parse this option */
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++*argv, --*argc;
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}
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else
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{
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/* The argument has to be a file name */
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png_image image;
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image.version = PNG_IMAGE_VERSION;
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if (png_image_begin_read_from_file(&image, (*argv)[0]))
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{
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png_uint_16p buffer;
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image.format = PNG_FORMAT_LINEAR_RGB_ALPHA;
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buffer = malloc(PNG_IMAGE_SIZE(image));
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if (buffer != NULL)
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{
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if (png_image_finish_read(&image, NULL/*background*/, buffer,
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0/*row_stride*/,
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NULL/*colormap for PNG_FORMAT_FLAG_COLORMAP*/))
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{
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/* This is the place were the Porter-Duff 'Over' operator
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* needs to be done by this code. In fact any image
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* processing required can be done here; the data is in
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* the correct format (linear, 16-bit) and source and
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* destination are in memory.
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*/
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sprite_op(sprite, x, y, &image, buffer);
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free(buffer);
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++*argv, --*argc;
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/* And continue to the next argument */
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continue;
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}
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else
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{
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free(buffer);
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fprintf(stderr, "simpleover: read %s: %s\n", (*argv)[0],
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image.message);
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}
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}
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else
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{
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fprintf(stderr, "simpleover: out of memory: %lu bytes\n",
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(unsigned long)PNG_IMAGE_SIZE(image));
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/* png_image_free must be called if we abort the Simplified API
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* read because of a problem detected in this code. If problems
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* are detected in the Simplified API it cleans up itself.
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*/
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png_image_free(&image);
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}
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}
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else
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{
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/* Failed to read the first argument: */
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fprintf(stderr, "simpleover: %s: %s\n", (*argv)[0], image.message);
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}
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return 0; /* failure */
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}
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}
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/* All the sprite operations have completed successfully, save the RGBA
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* buffer as a PNG using the simplified write API.
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*/
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sprite->file = tmpfile();
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if (sprite->file != NULL)
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{
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png_image save;
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memset(&save, 0, sizeof save);
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save.version = PNG_IMAGE_VERSION;
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save.opaque = NULL;
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save.width = sprite->width;
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save.height = sprite->height;
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save.format = PNG_FORMAT_LINEAR_RGB_ALPHA;
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save.flags = PNG_IMAGE_FLAG_FAST;
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save.colormap_entries = 0;
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if (png_image_write_to_stdio(&save, sprite->file, 1/*convert_to_8_bit*/,
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sprite->buffer, 0/*row_stride*/, NULL/*colormap*/))
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{
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/* Success, the buffer is no longer needed: */
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free(sprite->buffer);
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sprite->buffer = NULL;
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return 1; /* ok */
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}
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else
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fprintf(stderr, "simpleover: write sprite %s: %s\n", sprite->name,
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save.message);
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}
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else
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fprintf(stderr, "simpleover: sprite %s: could not allocate tmpfile: %s\n",
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sprite->name, strerror(errno));
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return 0; /* fail */
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}
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static int
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add_sprite(png_imagep output, png_bytep out_buf, struct sprite *sprite,
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int *argc, const char ***argv)
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{
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/* Given a --add argument naming this sprite perform the operations listed
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* in the following arguments. The arguments are expected to have the form
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* (x,y), which is just an offset at which to add the sprite to the
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* output.
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*/
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while (*argc > 0)
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{
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char tombstone;
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int x, y;
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if ((*argv)[0][0] == '-' && (*argv)[0][1] == '-')
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return 1; /* success */
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if (sscanf((*argv)[0], "%d,%d%c", &x, &y, &tombstone) == 2)
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{
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/* Now add the new image into the sprite data, but only if it
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* will fit.
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*/
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if (x < 0 || y < 0 ||
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(unsigned)/*SAFE*/x >= output->width ||
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(unsigned)/*SAFE*/y >= output->height ||
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sprite->width > output->width-x ||
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sprite->height > output->height-y)
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{
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fprintf(stderr, "simpleover: sprite %s @ (%d,%d) outside image\n",
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sprite->name, x, y);
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/* Could just skip this, but for the moment it is an error */
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return 0; /* error */
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}
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else
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{
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/* Since we know the sprite fits we can just read it into the
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* output using the simplified API.
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*/
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png_image in;
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in.version = PNG_IMAGE_VERSION;
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rewind(sprite->file);
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if (png_image_begin_read_from_stdio(&in, sprite->file))
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{
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in.format = PNG_FORMAT_RGB; /* force compose */
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if (png_image_finish_read(&in, NULL/*background*/,
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out_buf + (y*output->width + x)*3/*RGB*/,
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output->width*3/*row_stride*/,
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NULL/*colormap for PNG_FORMAT_FLAG_COLORMAP*/))
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{
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++*argv, --*argc;
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continue;
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}
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}
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/* The read failed: */
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fprintf(stderr, "simpleover: add sprite %s: %s\n", sprite->name,
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in.message);
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return 0; /* error */
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}
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}
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else
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{
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fprintf(stderr, "simpleover: --add='%s': invalid position %s\n",
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sprite->name, (*argv)[0]);
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return 0; /* error */
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}
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}
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return 1; /* ok */
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}
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static int
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simpleover_process(png_imagep output, png_bytep out_buf, int argc,
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const char **argv)
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{
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int result = 1; /* success */
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# define csprites 10/*limit*/
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# define str(a) #a
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int nsprites = 0;
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struct sprite sprites[csprites];
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while (argc > 0)
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{
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result = 0; /* fail */
|
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if (strncmp(argv[0], "--sprite=", 9) == 0)
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{
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char tombstone;
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if (nsprites < csprites)
|
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{
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int n;
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sprites[nsprites].width = sprites[nsprites].height = 0;
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sprites[nsprites].name[0] = 0;
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n = sscanf(argv[0], "--sprite=%u,%u,%" str(sprite_name_chars) "s%c",
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&sprites[nsprites].width, &sprites[nsprites].height,
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sprites[nsprites].name, &tombstone);
|
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if ((n == 2 || n == 3) &&
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sprites[nsprites].width > 0 && sprites[nsprites].height > 0)
|
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{
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size_t buf_size, tmp;
|
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|
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/* Default a name if not given. */
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if (sprites[nsprites].name[0] == 0)
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sprintf(sprites[nsprites].name, "sprite-%d", nsprites+1);
|
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|
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/* Allocate a buffer for the sprite, calculate the buffer
|
||||
* size:
|
||||
*/
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buf_size = sizeof (png_uint_16 [4]);
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buf_size *= sprites[nsprites].width;
|
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buf_size *= sprites[nsprites].height;
|
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|
||||
/* This can overflow a (size_t), check for this: */
|
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tmp = buf_size;
|
||||
tmp /= sprites[nsprites].width;
|
||||
tmp /= sprites[nsprites].height;
|
||||
|
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if (tmp == sizeof (png_uint_16 [4]))
|
||||
{
|
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sprites[nsprites].buffer = malloc(buf_size);
|
||||
/* This buffer must be initialized to transparent: */
|
||||
memset(sprites[nsprites].buffer, 0, buf_size);
|
||||
|
||||
if (sprites[nsprites].buffer != NULL)
|
||||
{
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sprites[nsprites].file = NULL;
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++argv, --argc;
|
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|
||||
if (create_sprite(sprites+nsprites++, &argc, &argv))
|
||||
{
|
||||
result = 1; /* still ok */
|
||||
continue;
|
||||
}
|
||||
|
||||
break; /* error */
|
||||
}
|
||||
}
|
||||
|
||||
/* Overflow, or OOM */
|
||||
fprintf(stderr, "simpleover: %s: sprite too large\n", argv[0]);
|
||||
break;
|
||||
}
|
||||
|
||||
else
|
||||
{
|
||||
fprintf(stderr, "simpleover: %s: invalid sprite (%u,%u)\n",
|
||||
argv[0], sprites[nsprites].width, sprites[nsprites].height);
|
||||
break;
|
||||
}
|
||||
}
|
||||
|
||||
else
|
||||
{
|
||||
fprintf(stderr, "simpleover: %s: too many sprites\n", argv[0]);
|
||||
break;
|
||||
}
|
||||
}
|
||||
|
||||
else if (strncmp(argv[0], "--add=", 6) == 0)
|
||||
{
|
||||
const char *name = argv[0]+6;
|
||||
int isprite = nsprites;
|
||||
|
||||
++argv, --argc;
|
||||
|
||||
while (--isprite >= 0)
|
||||
{
|
||||
if (strcmp(sprites[isprite].name, name) == 0)
|
||||
{
|
||||
if (!add_sprite(output, out_buf, sprites+isprite, &argc, &argv))
|
||||
goto out; /* error in addspite */
|
||||
|
||||
break;
|
||||
}
|
||||
}
|
||||
|
||||
if (isprite < 0) /* sprite not found */
|
||||
{
|
||||
fprintf(stderr, "simpleover: --add='%s': sprite not found\n", name);
|
||||
break;
|
||||
}
|
||||
}
|
||||
|
||||
else
|
||||
{
|
||||
fprintf(stderr, "simpleover: %s: unrecognized operation\n", argv[0]);
|
||||
break;
|
||||
}
|
||||
|
||||
result = 1; /* ok */
|
||||
}
|
||||
|
||||
/* Clean up the cache of sprites: */
|
||||
out:
|
||||
while (--nsprites >= 0)
|
||||
{
|
||||
if (sprites[nsprites].buffer != NULL)
|
||||
free(sprites[nsprites].buffer);
|
||||
|
||||
if (sprites[nsprites].file != NULL)
|
||||
(void)fclose(sprites[nsprites].file);
|
||||
}
|
||||
|
||||
return result;
|
||||
}
|
||||
|
||||
int main(int argc, const char **argv)
|
||||
{
|
||||
int result = 1; /* default to fail */
|
||||
|
||||
if (argc >= 2)
|
||||
{
|
||||
int argi = 2;
|
||||
const char *output = NULL;
|
||||
png_image image;
|
||||
|
||||
if (argc > 2 && argv[2][0] != '-'/*an operation*/)
|
||||
{
|
||||
output = argv[2];
|
||||
argi = 3;
|
||||
}
|
||||
|
||||
image.version = PNG_IMAGE_VERSION;
|
||||
if (png_image_begin_read_from_file(&image, argv[1]))
|
||||
{
|
||||
png_bytep buffer;
|
||||
|
||||
image.format = PNG_FORMAT_RGB; /* 24-bit RGB */
|
||||
|
||||
buffer = malloc(PNG_IMAGE_SIZE(image));
|
||||
|
||||
if (buffer != NULL)
|
||||
{
|
||||
png_color background = {0, 0xff, 0}; /* green (aka "lime") */
|
||||
|
||||
if (png_image_finish_read(&image, &background, buffer,
|
||||
0/*row_stride*/, NULL/*colormap for PNG_FORMAT_FLAG_COLORMAP */))
|
||||
{
|
||||
/* At this point png_image_finish_read has cleaned up the
|
||||
* allocated data in png_image, and only the buffer needs to be
|
||||
* freed.
|
||||
*
|
||||
* Perform the remaining operations:
|
||||
*/
|
||||
if (simpleover_process(&image, buffer, argc-argi, argv+argi))
|
||||
{
|
||||
/* Write the output: */
|
||||
if ((output != NULL &&
|
||||
png_image_write_to_file(&image, output,
|
||||
0/*convert_to_8bit*/, buffer, 0/*row_stride*/,
|
||||
NULL/*colormap*/)) ||
|
||||
(output == NULL &&
|
||||
png_image_write_to_stdio(&image, stdout,
|
||||
0/*convert_to_8bit*/, buffer, 0/*row_stride*/,
|
||||
NULL/*colormap*/)))
|
||||
result = 0;
|
||||
|
||||
else
|
||||
fprintf(stderr, "simpleover: write %s: %s\n",
|
||||
output == NULL ? "stdout" : output, image.message);
|
||||
}
|
||||
|
||||
/* else simpleover_process writes an error message */
|
||||
}
|
||||
|
||||
else
|
||||
fprintf(stderr, "simpleover: read %s: %s\n", argv[1],
|
||||
image.message);
|
||||
|
||||
free(buffer);
|
||||
}
|
||||
|
||||
else
|
||||
{
|
||||
fprintf(stderr, "simpleover: out of memory: %lu bytes\n",
|
||||
(unsigned long)PNG_IMAGE_SIZE(image));
|
||||
|
||||
/* This is the only place where a 'free' is required; libpng does
|
||||
* the cleanup on error and success, but in this case we couldn't
|
||||
* complete the read because of running out of memory.
|
||||
*/
|
||||
png_image_free(&image);
|
||||
}
|
||||
}
|
||||
|
||||
else
|
||||
{
|
||||
/* Failed to read the first argument: */
|
||||
fprintf(stderr, "simpleover: %s: %s\n", argv[1], image.message);
|
||||
}
|
||||
}
|
||||
|
||||
else
|
||||
{
|
||||
/* Usage message */
|
||||
fprintf(stderr,
|
||||
"simpleover: usage: simpleover background.png [output.png]\n"
|
||||
" Output 'background.png' as a 24-bit RGB PNG file in 'output.png'\n"
|
||||
" or, if not given, stdout. 'background.png' will be composited\n"
|
||||
" on green.\n"
|
||||
"\n"
|
||||
" Optionally, before output, process additional PNG files:\n"
|
||||
"\n"
|
||||
" --sprite=width,height,name {[--at=x,y] {sprite.png}}\n"
|
||||
" Produce a transparent sprite of size (width,height) and with\n"
|
||||
" name 'name'.\n"
|
||||
" For each sprite.png composite it using a Porter-Duff 'Over'\n"
|
||||
" operation at offset (x,y) in the sprite (defaulting to (0,0)).\n"
|
||||
" Input PNGs will be truncated to the area of the sprite.\n"
|
||||
"\n"
|
||||
" --add='name' {x,y}\n"
|
||||
" Optionally, before output, composite a sprite, 'name', which\n"
|
||||
" must have been previously produced using --sprite, at each\n"
|
||||
" offset (x,y) in the output image. Each sprite must fit\n"
|
||||
" completely within the output image.\n"
|
||||
"\n"
|
||||
" PNG files are processed in the order they occur on the command\n"
|
||||
" line and thus the first PNG processed appears as the bottommost\n"
|
||||
" in the output image.\n");
|
||||
}
|
||||
|
||||
return result;
|
||||
}
|
||||
Loading…
Reference in New Issue
Block a user