diff --git a/src/external/stb/stb_image_write.h b/src/external/stb/stb_image_write.h
index cffd473c1..e4b32ed1b 100644
--- a/src/external/stb/stb_image_write.h
+++ b/src/external/stb/stb_image_write.h
@@ -1,4 +1,4 @@
-/* stb_image_write - v1.14 - public domain - http://nothings.org/stb
+/* stb_image_write - v1.16 - public domain - http://nothings.org/stb
    writes out PNG/BMP/TGA/JPEG/HDR images to C stdio - Sean Barrett 2010-2015
                                      no warranty implied; use at your own risk
 
@@ -140,6 +140,7 @@ CREDITS:
       Ivan Tikhonov
       github:ignotion
       Adam Schackart
+      Andrew Kensler
 
 LICENSE
 
@@ -166,9 +167,9 @@ LICENSE
 #endif
 
 #ifndef STB_IMAGE_WRITE_STATIC  // C++ forbids static forward declarations
-extern int stbi_write_tga_with_rle;
-extern int stbi_write_png_compression_level;
-extern int stbi_write_force_png_filter;
+STBIWDEF int stbi_write_tga_with_rle;
+STBIWDEF int stbi_write_png_compression_level;
+STBIWDEF int stbi_write_force_png_filter;
 #endif
 
 #ifndef STBI_WRITE_NO_STDIO
@@ -178,7 +179,7 @@ STBIWDEF int stbi_write_tga(char const *filename, int w, int h, int comp, const
 STBIWDEF int stbi_write_hdr(char const *filename, int w, int h, int comp, const float *data);
 STBIWDEF int stbi_write_jpg(char const *filename, int x, int y, int comp, const void  *data, int quality);
 
-#ifdef STBI_WINDOWS_UTF8
+#ifdef STBIW_WINDOWS_UTF8
 STBIWDEF int stbiw_convert_wchar_to_utf8(char *buffer, size_t bufferlen, const wchar_t* input);
 #endif
 #endif
@@ -267,6 +268,8 @@ typedef struct
 {
    stbi_write_func *func;
    void *context;
+   unsigned char buffer[64];
+   int buf_used;
 } stbi__write_context;
 
 // initialize a callback-based context
@@ -283,7 +286,7 @@ static void stbi__stdio_write(void *context, void *data, int size)
    fwrite(data,1,size,(FILE*) context);
 }
 
-#if defined(_MSC_VER) && defined(STBI_WINDOWS_UTF8)
+#if defined(_WIN32) && defined(STBIW_WINDOWS_UTF8)
 #ifdef __cplusplus
 #define STBIW_EXTERN extern "C"
 #else
@@ -294,25 +297,25 @@ STBIW_EXTERN __declspec(dllimport) int __stdcall WideCharToMultiByte(unsigned in
 
 STBIWDEF int stbiw_convert_wchar_to_utf8(char *buffer, size_t bufferlen, const wchar_t* input)
 {
-	return WideCharToMultiByte(65001 /* UTF8 */, 0, input, -1, buffer, (int) bufferlen, NULL, NULL);
+   return WideCharToMultiByte(65001 /* UTF8 */, 0, input, -1, buffer, (int) bufferlen, NULL, NULL);
 }
 #endif
 
 static FILE *stbiw__fopen(char const *filename, char const *mode)
 {
    FILE *f;
-#if defined(_MSC_VER) && defined(STBI_WINDOWS_UTF8)
+#if defined(_WIN32) && defined(STBIW_WINDOWS_UTF8)
    wchar_t wMode[64];
    wchar_t wFilename[1024];
-	if (0 == MultiByteToWideChar(65001 /* UTF8 */, 0, filename, -1, wFilename, sizeof(wFilename)))
+   if (0 == MultiByteToWideChar(65001 /* UTF8 */, 0, filename, -1, wFilename, sizeof(wFilename)/sizeof(*wFilename)))
       return 0;
 
-	if (0 == MultiByteToWideChar(65001 /* UTF8 */, 0, mode, -1, wMode, sizeof(wMode)))
+   if (0 == MultiByteToWideChar(65001 /* UTF8 */, 0, mode, -1, wMode, sizeof(wMode)/sizeof(*wMode)))
       return 0;
 
-#if _MSC_VER >= 1400
-	if (0 != _wfopen_s(&f, wFilename, wMode))
-		f = 0;
+#if defined(_MSC_VER) && _MSC_VER >= 1400
+   if (0 != _wfopen_s(&f, wFilename, wMode))
+      f = 0;
 #else
    f = _wfopen(wFilename, wMode);
 #endif
@@ -380,16 +383,36 @@ static void stbiw__writef(stbi__write_context *s, const char *fmt, ...)
    va_end(v);
 }
 
+static void stbiw__write_flush(stbi__write_context *s)
+{
+   if (s->buf_used) {
+      s->func(s->context, &s->buffer, s->buf_used);
+      s->buf_used = 0;
+   }
+}
+
 static void stbiw__putc(stbi__write_context *s, unsigned char c)
 {
    s->func(s->context, &c, 1);
 }
 
+static void stbiw__write1(stbi__write_context *s, unsigned char a)
+{
+   if ((size_t)s->buf_used + 1 > sizeof(s->buffer))
+      stbiw__write_flush(s);
+   s->buffer[s->buf_used++] = a;
+}
+
 static void stbiw__write3(stbi__write_context *s, unsigned char a, unsigned char b, unsigned char c)
 {
-   unsigned char arr[3];
-   arr[0] = a; arr[1] = b; arr[2] = c;
-   s->func(s->context, arr, 3);
+   int n;
+   if ((size_t)s->buf_used + 3 > sizeof(s->buffer))
+      stbiw__write_flush(s);
+   n = s->buf_used;
+   s->buf_used = n+3;
+   s->buffer[n+0] = a;
+   s->buffer[n+1] = b;
+   s->buffer[n+2] = c;
 }
 
 static void stbiw__write_pixel(stbi__write_context *s, int rgb_dir, int comp, int write_alpha, int expand_mono, unsigned char *d)
@@ -398,7 +421,7 @@ static void stbiw__write_pixel(stbi__write_context *s, int rgb_dir, int comp, in
    int k;
 
    if (write_alpha < 0)
-      s->func(s->context, &d[comp - 1], 1);
+      stbiw__write1(s, d[comp - 1]);
 
    switch (comp) {
       case 2: // 2 pixels = mono + alpha, alpha is written separately, so same as 1-channel case
@@ -406,7 +429,7 @@ static void stbiw__write_pixel(stbi__write_context *s, int rgb_dir, int comp, in
          if (expand_mono)
             stbiw__write3(s, d[0], d[0], d[0]); // monochrome bmp
          else
-            s->func(s->context, d, 1);  // monochrome TGA
+            stbiw__write1(s, d[0]);  // monochrome TGA
          break;
       case 4:
          if (!write_alpha) {
@@ -422,7 +445,7 @@ static void stbiw__write_pixel(stbi__write_context *s, int rgb_dir, int comp, in
          break;
    }
    if (write_alpha > 0)
-      s->func(s->context, &d[comp - 1], 1);
+      stbiw__write1(s, d[comp - 1]);
 }
 
 static void stbiw__write_pixels(stbi__write_context *s, int rgb_dir, int vdir, int x, int y, int comp, void *data, int write_alpha, int scanline_pad, int expand_mono)
@@ -447,6 +470,7 @@ static void stbiw__write_pixels(stbi__write_context *s, int rgb_dir, int vdir, i
          unsigned char *d = (unsigned char *) data + (j*x+i)*comp;
          stbiw__write_pixel(s, rgb_dir, comp, write_alpha, expand_mono, d);
       }
+      stbiw__write_flush(s);
       s->func(s->context, &zero, scanline_pad);
    }
 }
@@ -467,16 +491,27 @@ static int stbiw__outfile(stbi__write_context *s, int rgb_dir, int vdir, int x,
 
 static int stbi_write_bmp_core(stbi__write_context *s, int x, int y, int comp, const void *data)
 {
-   int pad = (-x*3) & 3;
-   return stbiw__outfile(s,-1,-1,x,y,comp,1,(void *) data,0,pad,
-           "11 4 22 4" "4 44 22 444444",
-           'B', 'M', 14+40+(x*3+pad)*y, 0,0, 14+40,  // file header
-            40, x,y, 1,24, 0,0,0,0,0,0);             // bitmap header
+   if (comp != 4) {
+      // write RGB bitmap
+      int pad = (-x*3) & 3;
+      return stbiw__outfile(s,-1,-1,x,y,comp,1,(void *) data,0,pad,
+              "11 4 22 4" "4 44 22 444444",
+              'B', 'M', 14+40+(x*3+pad)*y, 0,0, 14+40,  // file header
+               40, x,y, 1,24, 0,0,0,0,0,0);             // bitmap header
+   } else {
+      // RGBA bitmaps need a v4 header
+      // use BI_BITFIELDS mode with 32bpp and alpha mask
+      // (straight BI_RGB with alpha mask doesn't work in most readers)
+      return stbiw__outfile(s,-1,-1,x,y,comp,1,(void *)data,1,0,
+         "11 4 22 4" "4 44 22 444444 4444 4 444 444 444 444",
+         'B', 'M', 14+108+x*y*4, 0, 0, 14+108, // file header
+         108, x,y, 1,32, 3,0,0,0,0,0, 0xff0000,0xff00,0xff,0xff000000u, 0, 0,0,0, 0,0,0, 0,0,0, 0,0,0); // bitmap V4 header
+   }
 }
 
 STBIWDEF int stbi_write_bmp_to_func(stbi_write_func *func, void *context, int x, int y, int comp, const void *data)
 {
-   stbi__write_context s;
+   stbi__write_context s = { 0 };
    stbi__start_write_callbacks(&s, func, context);
    return stbi_write_bmp_core(&s, x, y, comp, data);
 }
@@ -484,7 +519,7 @@ STBIWDEF int stbi_write_bmp_to_func(stbi_write_func *func, void *context, int x,
 #ifndef STBI_WRITE_NO_STDIO
 STBIWDEF int stbi_write_bmp(char const *filename, int x, int y, int comp, const void *data)
 {
-   stbi__write_context s;
+   stbi__write_context s = { 0 };
    if (stbi__start_write_file(&s,filename)) {
       int r = stbi_write_bmp_core(&s, x, y, comp, data);
       stbi__end_write_file(&s);
@@ -557,24 +592,25 @@ static int stbi_write_tga_core(stbi__write_context *s, int x, int y, int comp, v
 
             if (diff) {
                unsigned char header = STBIW_UCHAR(len - 1);
-               s->func(s->context, &header, 1);
+               stbiw__write1(s, header);
                for (k = 0; k < len; ++k) {
                   stbiw__write_pixel(s, -1, comp, has_alpha, 0, begin + k * comp);
                }
             } else {
                unsigned char header = STBIW_UCHAR(len - 129);
-               s->func(s->context, &header, 1);
+               stbiw__write1(s, header);
                stbiw__write_pixel(s, -1, comp, has_alpha, 0, begin);
             }
          }
       }
+      stbiw__write_flush(s);
    }
    return 1;
 }
 
 STBIWDEF int stbi_write_tga_to_func(stbi_write_func *func, void *context, int x, int y, int comp, const void *data)
 {
-   stbi__write_context s;
+   stbi__write_context s = { 0 };
    stbi__start_write_callbacks(&s, func, context);
    return stbi_write_tga_core(&s, x, y, comp, (void *) data);
 }
@@ -582,7 +618,7 @@ STBIWDEF int stbi_write_tga_to_func(stbi_write_func *func, void *context, int x,
 #ifndef STBI_WRITE_NO_STDIO
 STBIWDEF int stbi_write_tga(char const *filename, int x, int y, int comp, const void *data)
 {
-   stbi__write_context s;
+   stbi__write_context s = { 0 };
    if (stbi__start_write_file(&s,filename)) {
       int r = stbi_write_tga_core(&s, x, y, comp, (void *) data);
       stbi__end_write_file(&s);
@@ -598,6 +634,8 @@ STBIWDEF int stbi_write_tga(char const *filename, int x, int y, int comp, const
 
 #define stbiw__max(a, b)  ((a) > (b) ? (a) : (b))
 
+#ifndef STBI_WRITE_NO_STDIO
+
 static void stbiw__linear_to_rgbe(unsigned char *rgbe, float *linear)
 {
    int exponent;
@@ -732,7 +770,7 @@ static int stbi_write_hdr_core(stbi__write_context *s, int x, int y, int comp, f
       char header[] = "#?RADIANCE\n# Written by stb_image_write.h\nFORMAT=32-bit_rle_rgbe\n";
       s->func(s->context, header, sizeof(header)-1);
 
-#ifdef __STDC_WANT_SECURE_LIB__
+#ifdef __STDC_LIB_EXT1__
       len = sprintf_s(buffer, sizeof(buffer), "EXPOSURE=          1.0000000000000\n\n-Y %d +X %d\n", y, x);
 #else
       len = sprintf(buffer, "EXPOSURE=          1.0000000000000\n\n-Y %d +X %d\n", y, x);
@@ -748,15 +786,14 @@ static int stbi_write_hdr_core(stbi__write_context *s, int x, int y, int comp, f
 
 STBIWDEF int stbi_write_hdr_to_func(stbi_write_func *func, void *context, int x, int y, int comp, const float *data)
 {
-   stbi__write_context s;
+   stbi__write_context s = { 0 };
    stbi__start_write_callbacks(&s, func, context);
    return stbi_write_hdr_core(&s, x, y, comp, (float *) data);
 }
 
-#ifndef STBI_WRITE_NO_STDIO
 STBIWDEF int stbi_write_hdr(char const *filename, int x, int y, int comp, const float *data)
 {
-   stbi__write_context s;
+   stbi__write_context s = { 0 };
    if (stbi__start_write_file(&s,filename)) {
       int r = stbi_write_hdr_core(&s, x, y, comp, (float *) data);
       stbi__end_write_file(&s);
@@ -944,6 +981,23 @@ STBIWDEF unsigned char * stbi_zlib_compress(unsigned char *data, int data_len, i
       (void) stbiw__sbfree(hash_table[i]);
    STBIW_FREE(hash_table);
 
+   // store uncompressed instead if compression was worse
+   if (stbiw__sbn(out) > data_len + 2 + ((data_len+32766)/32767)*5) {
+      stbiw__sbn(out) = 2;  // truncate to DEFLATE 32K window and FLEVEL = 1
+      for (j = 0; j < data_len;) {
+         int blocklen = data_len - j;
+         if (blocklen > 32767) blocklen = 32767;
+         stbiw__sbpush(out, data_len - j == blocklen); // BFINAL = ?, BTYPE = 0 -- no compression
+         stbiw__sbpush(out, STBIW_UCHAR(blocklen)); // LEN
+         stbiw__sbpush(out, STBIW_UCHAR(blocklen >> 8));
+         stbiw__sbpush(out, STBIW_UCHAR(~blocklen)); // NLEN
+         stbiw__sbpush(out, STBIW_UCHAR(~blocklen >> 8));
+         memcpy(out+stbiw__sbn(out), data+j, blocklen);
+         stbiw__sbn(out) += blocklen;
+         j += blocklen;
+      }
+   }
+
    {
       // compute adler32 on input
       unsigned int s1=1, s2=0;
@@ -1552,7 +1606,7 @@ static int stbi_write_jpg_core(stbi__write_context *s, int width, int height, in
 
 STBIWDEF int stbi_write_jpg_to_func(stbi_write_func *func, void *context, int x, int y, int comp, const void *data, int quality)
 {
-   stbi__write_context s;
+   stbi__write_context s = { 0 };
    stbi__start_write_callbacks(&s, func, context);
    return stbi_write_jpg_core(&s, x, y, comp, (void *) data, quality);
 }
@@ -1561,7 +1615,7 @@ STBIWDEF int stbi_write_jpg_to_func(stbi_write_func *func, void *context, int x,
 #ifndef STBI_WRITE_NO_STDIO
 STBIWDEF int stbi_write_jpg(char const *filename, int x, int y, int comp, const void *data, int quality)
 {
-   stbi__write_context s;
+   stbi__write_context s = { 0 };
    if (stbi__start_write_file(&s,filename)) {
       int r = stbi_write_jpg_core(&s, x, y, comp, data, quality);
       stbi__end_write_file(&s);
@@ -1574,6 +1628,10 @@ STBIWDEF int stbi_write_jpg(char const *filename, int x, int y, int comp, const
 #endif // STB_IMAGE_WRITE_IMPLEMENTATION
 
 /* Revision history
+      1.16  (2021-07-11)
+             make Deflate code emit uncompressed blocks when it would otherwise expand
+             support writing BMPs with alpha channel
+      1.15  (2020-07-13) unknown
       1.14  (2020-02-02) updated JPEG writer to downsample chroma channels
       1.13
       1.12
@@ -1611,7 +1669,7 @@ STBIWDEF int stbi_write_jpg(char const *filename, int x, int y, int comp, const
              add HDR output
              fix monochrome BMP
       0.95 (2014-08-17)
-		       add monochrome TGA output
+             add monochrome TGA output
       0.94 (2014-05-31)
              rename private functions to avoid conflicts with stb_image.h
       0.93 (2014-05-27)