kitchen: README + MISSIONS/engine-c keep-drop notes

engine-c/src/png.c

@@ -0,0 +1,83 @@
+/*
+ * Minimal dependency-free PNG encoder (RGBA) using zlib.
+ * Avoids linking SDL2_image (which drags in an incompatible SDL3 at runtime).
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "kknd.h"
+#include <zlib.h>
+
+static uint32_t crc_table[256];
+static int crc_done = 0;
+
+static void crc_init(void) {
+    for (uint32_t n = 0; n < 256; n++) {
+        uint32_t c = n;
+        for (int k = 0; k < 8; k++)
+            c = (c & 1) ? (0xedb88320U ^ (c >> 1)) : (c >> 1);
+        crc_table[n] = c;
+    }
+    crc_done = 1;
+}
+
+static uint32_t crc_update(uint32_t c, const uint8_t *buf, size_t len) {
+    c = ~c;
+    for (size_t i = 0; i < len; i++)
+        c = crc_table[(c ^ buf[i]) & 0xff] ^ (c >> 8);
+    return ~c;
+}
+
+static void chunk(FILE *f, const char *type, const uint8_t *data, uint32_t len) {
+    uint8_t hdr[4];
+    hdr[0] = (len >> 24) & 0xff; hdr[1] = (len >> 16) & 0xff;
+    hdr[2] = (len >> 8) & 0xff;  hdr[3] = len & 0xff;
+    fwrite(hdr, 1, 4, f);
+    fwrite(type, 1, 4, f);
+    if (len) fwrite(data, 1, len, f);
+    uint32_t crc = crc_update(0, (const uint8_t *)type, 4);
+    crc = crc_update(crc, data, len);
+    uint8_t cr[4];
+    cr[0] = (crc >> 24) & 0xff; cr[1] = (crc >> 16) & 0xff;
+    cr[2] = (crc >> 8) & 0xff;  cr[3] = crc & 0xff;
+    fwrite(cr, 1, 4, f);
+}
+
+int png_save(const char *path, int w, int h, const uint8_t *rgba) {
+    if (!crc_done) crc_init();
+    FILE *f = fopen(path, "wb");
+    if (!f) return -1;
+
+    static const uint8_t sig[8] = {137,80,78,71,13,10,26,10};
+    fwrite(sig, 1, 8, f);
+
+    uint8_t ihdr[13];
+    ihdr[0] = (w >> 24) & 0xff; ihdr[1] = (w >> 16) & 0xff;
+    ihdr[2] = (w >> 8) & 0xff;  ihdr[3] = w & 0xff;
+    ihdr[4] = (h >> 24) & 0xff; ihdr[5] = (h >> 16) & 0xff;
+    ihdr[6] = (h >> 8) & 0xff;  ihdr[7] = h & 0xff;
+    ihdr[8] = 8;   /* bit depth   */
+    ihdr[9] = 6;   /* colour type RGBA */
+    ihdr[10] = 0; ihdr[11] = 0; ihdr[12] = 0;
+    chunk(f, "IHDR", ihdr, 13);
+
+    /* raw scanlines with filter byte 0 */
+    uint8_t *raw = (uint8_t *)malloc((size_t)(w * 4 + 1) * h);
+    if (!raw) { fclose(f); return -1; }
+    for (int y = 0; y < h; y++) {
+        raw[(size_t)y * (w * 4 + 1)] = 0;
+        memcpy(raw + (size_t)y * (w * 4 + 1) + 1, rgba + (size_t)y * w * 4, (size_t)w * 4);
+    }
+    uLongf cmp_cap = compressBound((uLong)(w * 4 + 1) * h);
+    uint8_t *cmp = (uint8_t *)malloc(cmp_cap);
+    if (!cmp) { free(raw); fclose(f); return -1; }
+    uLongf cmp_len = cmp_cap;
+    compress2((Bytef *)cmp, &cmp_len, (const Bytef *)raw,
+              (uLong)(w * 4 + 1) * h, Z_BEST_COMPRESSION);
+    chunk(f, "IDAT", cmp, (uint32_t)cmp_len);
+    chunk(f, "IEND", NULL, 0);
+
+    free(cmp); free(raw);
+    fclose(f);
+    return 0;
+}