Add png2gs8 conversion utility.

png2gs8/Makefile

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+all: png2gs8
+
+png2gs8: png2gs8.c
+	$(CC) -O2 png2gs8.c `libpng-config --cflags` `libpng-config --L_opts` `libpng-config --libs` -lm -o png2gs8 -Wall -W
+
+clean:
+	rm -f png2gs8

png2gs8/README.md

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+This utility converts PNG images into 'gs8' files, that is an uncompressed
+representation of the image with a simple 4 bytes header:
+
+```
++-------+--------+----------//
+| width | heigth |  Image data... each byte between 0 - 255
++-------+--------+----------//
+```
+
+Width and height are big endian unsigned 16 bit integers.
+The converted images can be loaded by this driver and displayed on
+the screen.
+
+Compile with `make`, then:
+
+    ./png2gs8 dama_ermellino.png dama.gs8
+
+Then use the converted file as explained in the documentation for the driver.

png2gs8/png2gs8.c

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+/* Copyright (c) 2024, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   * Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <errno.h>
+#define PNG_DEBUG 3
+#include <png.h>
+
+/* Convert the PNG to into a raw RGB565 image that can be directly
+ * written to the ST77xx chip. The only added header is a composed of
+ * two 16 bit unsigned integers in big endian, width and height.
+ * The number of bytes of the image is always 4 + width*height*2 */
+#define PNG_BYTES_TO_CHECK 8
+void convert_png(char *iname, char *oname) {
+    unsigned char buf[PNG_BYTES_TO_CHECK];
+    png_structp png_ptr;
+    png_infop info_ptr;
+    png_uint_32 width, height, j;
+    int color_type;
+
+    /* Open the images for reading/writing. */
+    FILE *ifp = fopen(iname,"r");
+    if (ifp == NULL) {
+        perror("Opening input image");
+        exit(1);
+    }
+    FILE *ofp = fopen(oname,"w");
+    if (ofp == NULL) {
+        perror("Opening output image");
+        exit(1);
+    }
+
+    /* Check signature */
+    if (fread(buf, 1, PNG_BYTES_TO_CHECK, ifp) != PNG_BYTES_TO_CHECK ||
+        png_sig_cmp(buf, (png_size_t)0, PNG_BYTES_TO_CHECK))
+    {
+        fprintf(stderr,"Invalid PNG file");
+        return;
+    }
+
+    /* Initialize data structures */
+    png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
+        NULL,NULL,NULL);
+    if (png_ptr == NULL) {
+        perror("png_create_read_struct()");
+        exit(1);
+    }
+
+    info_ptr = png_create_info_struct(png_ptr);
+    if (info_ptr == NULL) {
+        perror("png_create_info_struct()");
+        exit(1);
+    }
+
+    /* Error handling code */
+    if (setjmp(png_jmpbuf(png_ptr)))
+    {
+        perror("setjmp() failed");
+        exit(1);
+    }
+
+    /* Set the I/O method */
+    png_init_io(png_ptr, ifp);
+
+    /* Undo the fact that we read some data to detect the PNG file */
+    png_set_sig_bytes(png_ptr, PNG_BYTES_TO_CHECK);
+
+    /* Read the PNG in memory at once */
+    png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_EXPAND, NULL);
+    width = png_get_image_width(png_ptr, info_ptr);
+    height = png_get_image_height(png_ptr, info_ptr);
+    color_type = png_get_color_type(png_ptr, info_ptr);
+
+    /* Write output image header. */
+    unsigned char hdr[4];
+    hdr[0] = width>>8;
+    hdr[1] = width&0xff;
+    hdr[2] = height>>8;
+    hdr[3] = height&0xff;
+    if (fwrite(hdr,4,1,ofp) != 1) {
+        perror("Writing to output file)");
+        exit(1);
+    }
+
+    char *color_str = "unknown";
+    switch(color_type) {
+    case PNG_COLOR_TYPE_RGB: color_str = "RGB"; break;
+    case PNG_COLOR_TYPE_RGB_ALPHA: color_str = "RGBA"; break;
+    case PNG_COLOR_TYPE_GRAY: color_str = "GRAY"; break;
+    case PNG_COLOR_TYPE_GRAY_ALPHA: color_str = "GRAYA"; break;
+    case PNG_COLOR_TYPE_PALETTE: color_str = "PALETTE"; break;
+    }
+
+    fprintf(stderr,"%dx%d image, color:%s\n",(int)width,(int)height,color_str);
+    if (color_type != PNG_COLOR_TYPE_RGB &&
+        color_type != PNG_COLOR_TYPE_RGB_ALPHA &&
+        color_type != PNG_COLOR_TYPE_GRAY &&
+        color_type != PNG_COLOR_TYPE_GRAY_ALPHA)
+    {
+        fprintf(stderr,"Unsupported PNG color type.");
+        exit(1);
+    }
+
+    /* Get the image data */
+    unsigned char **imageData = png_get_rows(png_ptr, info_ptr);
+
+    for (j = 0; j < height; j++) {
+        unsigned char *src = imageData[j];
+        unsigned int i, r, g, b;
+
+        for (i = 0; i < width; i++) {
+            if (color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
+                color_type == PNG_COLOR_TYPE_RGB)
+            {
+                r = src[0];
+                g = src[1];
+                b = src[2];
+                src += (color_type == PNG_COLOR_TYPE_RGB_ALPHA) ? 4 : 3;
+            } else if (color_type == PNG_COLOR_TYPE_GRAY_ALPHA ||
+                       color_type == PNG_COLOR_TYPE_GRAY)
+            {
+                r = b = g = src[0];
+                src += (color_type == PNG_COLOR_TYPE_GRAY_ALPHA) ? 2 : 1;
+            }
+            double lum = 0.299*r + 0.587*g + 0.114*b;
+            buf[0] = (int)lum;
+            if (fwrite(buf,1,1,ofp) != 1) {
+                perror("Writing to output file)");
+                exit(1);
+            }
+        }
+    }
+
+    /* Free the image and resources and return */
+    png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
+    fclose(ifp);
+    fclose(ofp);
+}
+
+int main(int argc, char **argv)
+{
+    if (argc != 3) {
+        fprintf(stderr,"Usage: %s image.png image.565\n",argv[0]);
+        exit(1);
+    }
+    convert_png(argv[1],argv[2]);
+    return 0;
+}