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This patch will allow PNG files to be saved.

Index: IMG_png.c
===================================================================
--- IMG_png.c	(revision 4475)
+++ IMG_png.c	(working copy)
@@ -76,17 +76,26 @@
 	png_infop (*png_create_info_struct) (png_structp png_ptr);
 	png_structp (*png_create_read_struct) (png_const_charp user_png_ver, png_voidp error_ptr, png_error_ptr error_fn, png_error_ptr warn_fn);
 	void (*png_destroy_read_struct) (png_structpp png_ptr_ptr, png_infopp info_ptr_ptr, png_infopp end_info_ptr_ptr);
+	png_structp (*png_create_write_struct) (png_const_charp user_png_ver, png_voidp error_ptr, png_error_ptr error_fn, png_error_ptr warn_fn);
+	void (*png_destroy_write_struct) (png_structpp png_ptr_ptr, png_infopp info_ptr_ptr);
 	png_uint_32 (*png_get_IHDR) (png_structp png_ptr, png_infop info_ptr, png_uint_32 *width, png_uint_32 *height, int *bit_depth, int *color_type, int *interlace_method, int *compression_method, int *filter_method);
+	void (*png_set_IHDR) (png_structp png_ptr, png_infop info_ptr, png_uint_32 width, png_uint_32 height, int bit_depth, int color_type, int interlace_method, int compression_method, int filter_method);
 	png_voidp (*png_get_io_ptr) (png_structp png_ptr);
 	png_uint_32 (*png_get_tRNS) (png_structp png_ptr, png_infop info_ptr, png_bytep *trans, int *num_trans, png_color_16p *trans_values);
 	png_uint_32 (*png_get_valid) (png_structp png_ptr, png_infop info_ptr, png_uint_32 flag);
 	void (*png_read_image) (png_structp png_ptr, png_bytepp image);
+	void (*png_write_image) (png_structp png_ptr, png_bytepp image);
 	void (*png_read_info) (png_structp png_ptr, png_infop info_ptr);
+	void (*png_write_info) (png_structp png_ptr, png_infop info_ptr);
+	void (*png_set_PLTE) (png_structp png_ptr, png_infop info_ptr, png_colorp palette, int num_palette);
+	void (*png_write_end) (png_structp png_ptr, png_infop info_ptr);
 	void (*png_read_update_info) (png_structp png_ptr, png_infop info_ptr);
 	void (*png_set_expand) (png_structp png_ptr);
 	void (*png_set_gray_to_rgb) (png_structp png_ptr);
+	void (*png_set_bgr) (png_structp png_ptr);
 	void (*png_set_packing) (png_structp png_ptr);
 	void (*png_set_read_fn) (png_structp png_ptr, png_voidp io_ptr, png_rw_ptr read_data_fn);
+	void (*png_set_write_fn) (png_structp png_ptr, png_voidp io_ptr, png_rw_ptr read_data_fn);
 	void (*png_set_strip_16) (png_structp png_ptr);
 	int (*png_sig_cmp) (png_bytep sig, png_size_t start, png_size_t num_to_check);
 } lib;
@@ -120,6 +129,20 @@
 			SDL_UnloadObject(lib.handle);
 			return -1;
 		}
+		lib.png_create_write_struct =
+			(png_structp (*) (png_const_charp, png_voidp, png_error_ptr, png_error_ptr))
+			SDL_LoadFunction(lib.handle, "png_create_write_struct");
+		if ( lib.png_create_write_struct == NULL ) {
+			SDL_UnloadObject(lib.handle);
+			return -1;
+		}
+		lib.png_destroy_write_struct =
+			(void (*) (png_structpp, png_infopp))
+			SDL_LoadFunction(lib.handle, "png_destroy_write_struct");
+		if ( lib.png_destroy_write_struct == NULL ) {
+			SDL_UnloadObject(lib.handle);
+			return -1;
+		}
 		lib.png_get_IHDR =
 			(png_uint_32 (*) (png_structp, png_infop, png_uint_32 *, png_uint_32 *, int *, int *, int *, int *, int *))
 			SDL_LoadFunction(lib.handle, "png_get_IHDR");
@@ -127,6 +150,13 @@
 			SDL_UnloadObject(lib.handle);
 			return -1;
 		}
+		lib.png_set_IHDR =
+			(void (*) (png_structp, png_infop, png_uint_32, png_uint_32, int, int, int, int, int))
+			SDL_LoadFunction(lib.handle, "png_set_IHDR");
+		if ( lib.png_set_IHDR == NULL ) {
+			SDL_UnloadObject(lib.handle);
+			return -1;
+		}
 		lib.png_get_io_ptr =
 			(png_voidp (*) (png_structp))
 			SDL_LoadFunction(lib.handle, "png_get_io_ptr");
@@ -155,6 +185,13 @@
 			SDL_UnloadObject(lib.handle);
 			return -1;
 		}
+		lib.png_write_image =
+			(void (*) (png_structp, png_bytepp))
+			SDL_LoadFunction(lib.handle, "png_write_image");
+		if ( lib.png_write_image == NULL ) {
+			SDL_UnloadObject(lib.handle);
+			return -1;
+		}
 		lib.png_read_info =
 			(void (*) (png_structp, png_infop))
 			SDL_LoadFunction(lib.handle, "png_read_info");
@@ -162,6 +199,27 @@
 			SDL_UnloadObject(lib.handle);
 			return -1;
 		}
+		lib.png_write_info =
+			(void (*) (png_structp, png_infop))
+			SDL_LoadFunction(lib.handle, "png_write_info");
+		if ( lib.png_write_info == NULL ) {
+			SDL_UnloadObject(lib.handle);
+			return -1;
+		}	
+		lib.png_set_PLTE =
+			(void (*) (png_structp, png_infop, png_colorp, int))
+			SDL_LoadFunction(lib.handle, "png_set_PLTE");
+		if ( lib.png_set_PLTE == NULL ) {
+			SDL_UnloadObject(lib.handle);
+			return -1;
+		}
+		lib.png_write_end =
+			(void (*) (png_structp, png_infop))
+			SDL_LoadFunction(lib.handle, "png_write_end");
+		if ( lib.png_write_end == NULL ) {
+			SDL_UnloadObject(lib.handle);
+			return -1;
+		}
 		lib.png_read_update_info =
 			(void (*) (png_structp, png_infop))
 			SDL_LoadFunction(lib.handle, "png_read_update_info");
@@ -183,6 +241,13 @@
 			SDL_UnloadObject(lib.handle);
 			return -1;
 		}
+		lib.png_set_bgr =
+			(void (*) (png_structp))
+			SDL_LoadFunction(lib.handle, "png_set_bgr");
+		if ( lib.png_set_bgr == NULL ) {
+			SDL_UnloadObject(lib.handle);
+			return -1;
+		}
 		lib.png_set_packing =
 			(void (*) (png_structp))
 			SDL_LoadFunction(lib.handle, "png_set_packing");
@@ -197,6 +262,13 @@
 			SDL_UnloadObject(lib.handle);
 			return -1;
 		}
+		lib.png_set_write_fn =
+			(void (*) (png_structp, png_voidp, png_rw_ptr))
+			SDL_LoadFunction(lib.handle, "png_set_write_fn");
+		if ( lib.png_set_write_fn == NULL ) {
+			SDL_UnloadObject(lib.handle);
+			return -1;
+		}
 		lib.png_set_strip_16 =
 			(void (*) (png_structp))
 			SDL_LoadFunction(lib.handle, "png_set_strip_16");
@@ -505,6 +577,171 @@
 	return(surface); 
 }
 
+static void png_write_data(png_structp ctx, png_bytep area, png_size_t size)
+{
+	SDL_RWops *src;
+
+	src = (SDL_RWops *)lib.png_get_io_ptr(ctx);
+	SDL_RWwrite(src, area, size, 1);
+}
+/* write a png file */
+int IMG_SavePNG_RW(SDL_Surface *surface, SDL_RWops *src)
+{
+    png_structp png_ptr;
+    png_infop info_ptr;
+	png_colorp palette = NULL;
+    int start;
+	int colorType;
+	int i;
+    const char *error = NULL;
+	SDL_Palette *sdlPalette;
+	png_uint_32 height = surface->h;
+	png_uint_32 width = surface->w;
+	png_bytep *volatile row_pointers;
+	int row;
+
+	if ( !src ) {
+		/* The error message has been set in SDL_RWFromFile */
+		return -1;
+	}
+	start = SDL_RWtell(src);
+
+	if ( IMG_InitPNG() < 0 ) {
+		return -1;
+	}
+
+   /* Create and initialize the png_struct with the desired error handler
+    * functions.  If you want to use the default stderr and longjump method,
+    * you can supply NULL for the last three parameters.  We also check that
+    * the library version is compatible with the one used at compile time,
+    * in case we are using dynamically linked libraries.  REQUIRED.
+    */
+    png_ptr = NULL; info_ptr = NULL;
+
+	/* Create the PNG loading context structure */
+	png_ptr = lib.png_create_read_struct(PNG_LIBPNG_VER_STRING,
+					  NULL,NULL,NULL);
+	if (png_ptr == NULL){
+		error = "Couldn't allocate memory for PNG file or incompatible PNG dll";
+		goto done;
+	}
+
+	 /* Allocate/initialize the memory for image information.  REQUIRED. */
+	info_ptr = lib.png_create_info_struct(png_ptr);
+	if (info_ptr == NULL) {
+		error = "Couldn't create image information for PNG file";
+		goto done;
+	}
+
+	/* Set error handling if you are using setjmp/longjmp method (this is
+	 * the normal method of doing things with libpng).  REQUIRED unless you
+	 * set up your own error handlers in png_create_read_struct() earlier.
+	 */
+	if ( setjmp(png_ptr->jmpbuf) ) {
+		error = "Error reading the PNG file.";
+		goto done;
+	}
+
+	/* Set up the output control */
+    lib.png_set_write_fn(png_ptr, src, png_write_data);
+
+    /* Set the image information here.  Width and height are up to 2^31,
+     * bit_depth is one of 1, 2, 4, 8, or 16, but valid values also depend on
+     * the color_type selected. color_type is one of PNG_COLOR_TYPE_GRAY,
+     * PNG_COLOR_TYPE_GRAY_ALPHA, PNG_COLOR_TYPE_PALETTE, PNG_COLOR_TYPE_RGB,
+     * or PNG_COLOR_TYPE_RGB_ALPHA.  interlace is either PNG_INTERLACE_NONE or
+     * PNG_INTERLACE_ADAM7, and the compression_type and filter_type MUST
+     * currently be PNG_COMPRESSION_TYPE_BASE and PNG_FILTER_TYPE_BASE. REQUIRED
+     */
+	sdlPalette = surface->format->palette;
+	if (sdlPalette)
+	{		
+		colorType = PNG_COLOR_TYPE_PALETTE;
+	} else if (surface->format->Amask)
+	{
+		colorType = PNG_COLOR_TYPE_RGB_ALPHA;
+	} else
+	{
+		colorType = PNG_COLOR_TYPE_RGB;
+	}
+	lib.png_set_IHDR(png_ptr, info_ptr, surface->w, surface->h, surface->format->BitsPerPixel, colorType,
+		PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
+
+   /* set the palette if there is one.  REQUIRED for indexed-color images */
+	if (colorType == PNG_COLOR_TYPE_PALETTE)
+	{
+        palette = (png_colorp) malloc(sdlPalette->ncolors * sizeof(png_color));
+
+		for( i=0; i < sdlPalette->ncolors; ++i ) {
+		    palette[i].blue = sdlPalette->colors[i].b;
+		    palette[i].green = sdlPalette->colors[i].g;
+		    palette[i].red = sdlPalette->colors[i].r;
+		}
+		lib.png_set_PLTE(png_ptr, info_ptr, palette, sdlPalette->ncolors);
+	}
+	else
+	{ //not sure how to handle this
+//	    sig_bit.red = true_red_bit_depth;
+//	    sig_bit.green = true_green_bit_depth;
+//		sig_bit.blue = true_blue_bit_depth;
+	    /* if the image has an alpha channel then */
+//		sig_bit.alpha = true_alpha_bit_depth;
+//		png_set_sBIT(png_ptr, info_ptr, sig_bit);
+	}
+
+	lib.png_set_bgr(png_ptr);
+
+    /* Write the file header information.  REQUIRED */
+    lib.png_write_info(png_ptr, info_ptr);
+
+    /* The easiest way to write the image (you may have a different memory
+     * layout, however, so choose what fits your needs best).  You need to
+     * use the first method if you aren't handling interlacing yourself.
+     */
+
+	row_pointers = (png_bytep*) malloc(sizeof(png_bytep)*height);
+	if ( (row_pointers == NULL) ) {
+		error = "Out of memory";
+		goto done;
+	}
+	for (row = 0; row < (int)height; row++) {
+		row_pointers[row] = (png_bytep)
+				(Uint8 *)surface->pixels + row*surface->pitch;
+	}
+
+    if (height > PNG_UINT_32_MAX/sizeof(png_bytep))
+	{
+		error = "Image is too tall to process in memory";
+		goto done;
+	}
+
+	/* Read the entire image in one go */
+	lib.png_write_image(png_ptr, row_pointers);
+
+   /* It is REQUIRED to call this to finish writing the rest of the file */
+   lib.png_write_end(png_ptr, info_ptr);
+
+done:	/* Clean up and return */
+	if ( png_ptr ) {
+		lib.png_destroy_write_struct(&png_ptr, &info_ptr);
+	}
+	if ( row_pointers ) {
+		free(row_pointers);
+	}
+	if (palette)
+	{
+		free(palette);
+	}
+	if ( error ) {
+		IMG_QuitPNG();
+		IMG_SetError(error);
+		return(-1);
+	} else {
+		IMG_QuitPNG();
+	}
+	return(0); 
+}
+
 #else
 
 /* See if an image is contained in a data source */
Index: SDL_image.h
===================================================================
--- SDL_image.h	(revision 4475)
+++ SDL_image.h	(working copy)
@@ -107,6 +107,8 @@
 
 extern DECLSPEC SDL_Surface * SDLCALL IMG_ReadXPMFromArray(char **xpm);
 
+extern DECLSPEC int SDLCALL IMG_SavePNG_RW(SDL_Surface *surface, SDL_RWops *src);
+
 /* We'll use SDL for reporting errors */
 #define IMG_SetError	SDL_SetError
 #define IMG_GetError	SDL_GetError