tray: Save icons on *nix platforms to PNG instead of BMP

PNG has better compatibility with certain desktops.

This requires the stb_image_write header for PNG writing functionality.

src/tray/unix/SDL_tray.c

@@ -22,6 +22,7 @@
 #include "SDL_internal.h"
 
 #include "../SDL_tray_utils.h"
+#include "../../video/SDL_stb_c.h"
 
 #include <dlfcn.h>
 #include <errno.h>
@@ -184,7 +185,7 @@ static bool new_tmp_filename(SDL_Tray *tray)
 {
     static int count = 0;
 
-    int would_have_written = SDL_asprintf(&tray->icon_path, "%s/%d.bmp", tray->icon_dir, count++);
+    int would_have_written = SDL_asprintf(&tray->icon_path, "%s/%d.png", tray->icon_dir, count++);
 
     if (would_have_written >= 0) {
         return true;
@@ -289,7 +290,7 @@ SDL_Tray *SDL_CreateTray(SDL_Surface *icon, const char *tooltip)
             goto icon_dir_error;
         }
 
-        SDL_SaveBMP(icon, tray->icon_path);
+        SDL_SavePNG(icon, tray->icon_path);
     } else {
         // allocate a dummy icon path
         SDL_asprintf(&tray->icon_path, " ");
@@ -342,7 +343,7 @@ void SDL_SetTrayIcon(SDL_Tray *tray, SDL_Surface *icon)
     /* AppIndicator caches the icon files; always change filename to avoid caching */
 
     if (icon && new_tmp_filename(tray)) {
-        SDL_SaveBMP(icon, tray->icon_path);
+        SDL_SavePNG(icon, tray->icon_path);
         app_indicator_set_icon(tray->indicator, tray->icon_path);
     } else {
         SDL_free(tray->icon_path);

src/video/SDL_stb.c

@@ -21,7 +21,7 @@
 #include "SDL_internal.h"
 
 #include "SDL_stb_c.h"
-
+#include "SDL_surface_c.h"
 
 // We currently only support JPEG, but we could add other image formats if we wanted
 #ifdef SDL_HAVE_STB
@@ -59,6 +59,13 @@
 #define STB_IMAGE_IMPLEMENTATION
 #include "stb_image.h"
 
+#undef memcpy
+#define STB_IMAGE_WRITE_IMPLEMENTATION
+#define STB_IMAGE_WRITE_STATIC
+#define STBI_WRITE_NO_STDIO
+#define STBIW_ASSERT SDL_assert
+#include "stb_image_write.h"
+
 #undef memset
 #endif
 
@@ -119,3 +126,68 @@ bool SDL_ConvertPixels_STB(int width, int height,
     return SDL_SetError("SDL not built with STB image support");
 #endif
 }
+
+#ifdef SDL_HAVE_STB
+static void SDL_STBWriteFunc(void *context, void *data, int size)
+{
+    SDL_WriteIO(context, data, size);
+}
+#endif
+
+bool SDL_SavePNG_IO(SDL_Surface *surface, SDL_IOStream *dst, bool closeio)
+{
+#ifdef SDL_HAVE_STB
+    bool retval = true;
+
+    // Make sure we have somewhere to save
+    if (!SDL_SurfaceValid(surface)) {
+        retval = SDL_InvalidParamError("surface");
+        goto done;
+    }
+    if (!dst) {
+        retval = SDL_InvalidParamError("dst");
+        goto done;
+    }
+
+    bool free_surface = false;
+    if (surface->format != SDL_PIXELFORMAT_ABGR8888) {
+        surface = SDL_ConvertSurface(surface, SDL_PIXELFORMAT_ABGR8888);
+        if (!surface) {
+            retval = false;
+            goto done;
+        }
+        free_surface = true;
+    }
+
+    if (!stbi_write_png_to_func(SDL_STBWriteFunc, dst, surface->w, surface->h, 4, surface->pixels, surface->pitch)) {
+        retval = SDL_SetError("Failed to write PNG");
+    }
+
+    if (free_surface) {
+        SDL_DestroySurface(surface);
+    }
+
+done:
+    if (dst && closeio) {
+        retval = SDL_CloseIO(dst);
+    }
+
+    return retval;
+#else
+    return SDL_SetError("SDL not built with STB image write support");
+#endif
+}
+
+bool SDL_SavePNG(SDL_Surface *surface, const char *file)
+{
+#ifdef SDL_HAVE_STB
+    SDL_IOStream *stream = SDL_IOFromFile(file, "wb");
+    if (!stream) {
+        return false;
+    }
+
+    return SDL_SavePNG_IO(surface, stream, true);
+#else
+    return SDL_SetError("SDL not built with STB image write support");
+#endif
+}

src/video/SDL_stb_c.h

@@ -27,5 +27,7 @@
 // Image conversion functions
 
 extern bool SDL_ConvertPixels_STB(int width, int height, SDL_PixelFormat src_format, SDL_Colorspace src_colorspace, SDL_PropertiesID src_properties, const void *src, int src_pitch, SDL_PixelFormat dst_format, SDL_Colorspace dst_colorspace, SDL_PropertiesID dst_properties, void *dst, int dst_pitch);
+extern bool SDL_SavePNG_IO(SDL_Surface *surface, SDL_IOStream *dst, bool closeio);
+extern bool SDL_SavePNG(SDL_Surface *surface, const char *file);
 
 #endif // SDL_stb_c_h_