Added support for SDL_RENDERER_PRESENTVSYNC to the software renderer

This fixes https://github.com/libsdl-org/SDL/issues/4612

src/render/SDL_render.c

@@ -833,7 +833,8 @@ SDL_CreateRenderer(SDL_Window * window, int index, Uint32 flags)
         goto error;
     }
 
-    if (SDL_GetHint(SDL_HINT_RENDER_VSYNC)) {
+    hint = SDL_GetHint(SDL_HINT_RENDER_VSYNC);
+    if (hint && *hint) {
         if (SDL_GetHintBoolean(SDL_HINT_RENDER_VSYNC, SDL_TRUE)) {
             flags |= SDL_RENDERER_PRESENTVSYNC;
         } else {

src/render/software/SDL_render_sw.c

@@ -859,9 +859,22 @@ SW_CreateRendererForSurface(SDL_Surface * surface)
 static SDL_Renderer *
 SW_CreateRenderer(SDL_Window * window, Uint32 flags)
 {
+    const char *hint;
     SDL_Surface *surface;
 
+    /* Set the vsync hint based on our flags, if it's not already set */
+    hint = SDL_GetHint(SDL_HINT_RENDER_VSYNC);
+    if (!hint || !*hint) {
+        SDL_SetHint(SDL_HINT_RENDER_VSYNC, (flags & SDL_RENDERER_PRESENTVSYNC) ? "1" : "0");
+    }
+
     surface = SDL_GetWindowSurface(window);
+
+    /* Reset the vsync hint if we set it above */
+    if (!hint || !*hint) {
+        SDL_SetHint(SDL_HINT_RENDER_VSYNC, "");
+    }
+
     if (!surface) {
         return NULL;
     }
@@ -872,7 +885,7 @@ SDL_RenderDriver SW_RenderDriver = {
     SW_CreateRenderer,
     {
      "software",
-     SDL_RENDERER_SOFTWARE | SDL_RENDERER_TARGETTEXTURE,
+     SDL_RENDERER_SOFTWARE | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE,
      8,
      {
       SDL_PIXELFORMAT_ARGB8888,

src/video/SDL_video.c

@@ -172,53 +172,9 @@ typedef struct {
     int bytes_per_pixel;
 } SDL_WindowTextureData;
 
-static SDL_bool
-ShouldUseTextureFramebuffer()
-{
-    const char *hint;
-
-    /* If there's no native framebuffer support then there's no option */
-    if (!_this->CreateWindowFramebuffer) {
-        return SDL_TRUE;
-    }
-
-    /* If this is the dummy driver there is no texture support */
-    if (_this->is_dummy) {
-        return SDL_FALSE;
-    }
-
-    /* If the user has specified a software renderer we can't use a
-       texture framebuffer, or renderer creation will go recursive.
-     */
-    hint = SDL_GetHint(SDL_HINT_RENDER_DRIVER);
-    if (hint && SDL_strcasecmp(hint, "software") == 0) {
-        return SDL_FALSE;
-    }
-
-    /* See if the user or application wants a specific behavior */
-    hint = SDL_GetHint(SDL_HINT_FRAMEBUFFER_ACCELERATION);
-    if (hint) {
-        if (*hint == '0' || SDL_strcasecmp(hint, "false") == 0) {
-            return SDL_FALSE;
-        } else {
-            return SDL_TRUE;
-        }
-    }
-
-    /* Each platform has different performance characteristics */
-#if defined(__WIN32__)
-    /* GDI BitBlt() is way faster than Direct3D dynamic textures right now.
-     */
-    return SDL_FALSE;
-
-#elif defined(__MACOSX__)
-    /* Mac OS X uses OpenGL as the native fast path (for cocoa and X11) */
-    return SDL_TRUE;
-
-#elif defined(__LINUX__)
-    /* Properly configured OpenGL drivers are faster than MIT-SHM */
 #if SDL_VIDEO_OPENGL
-    /* Ugh, find a way to cache this value! */
+static SDL_bool
+HasAcceleratedOpenGL()
 {
     SDL_Window *window;
     SDL_GLContext context;
@@ -247,6 +203,50 @@ ShouldUseTextureFramebuffer()
     }
     return hasAcceleratedOpenGL;
 }
+#endif /* SDL_VIDEO_OPENGL */
+
+static SDL_bool
+ShouldUseTextureFramebuffer()
+{
+    const char *hint;
+
+    /* If there's no native framebuffer support then there's no option */
+    if (!_this->CreateWindowFramebuffer) {
+        return SDL_TRUE;
+    }
+
+    /* If this is the dummy driver there is no texture support */
+    if (_this->is_dummy) {
+        return SDL_FALSE;
+    }
+
+    /* See if the user or application wants a specific behavior */
+    hint = SDL_GetHint(SDL_HINT_FRAMEBUFFER_ACCELERATION);
+    if (hint) {
+        if (*hint == '0' || SDL_strcasecmp(hint, "false") == 0) {
+            return SDL_FALSE;
+        } else {
+            return SDL_TRUE;
+        }
+    }
+
+    /* Each platform has different performance characteristics */
+#if defined(__WIN32__)
+    /* GDI BitBlt() is way faster than Direct3D dynamic textures right now.
+     */
+    return SDL_FALSE;
+
+#elif defined(__MACOSX__)
+    /* Mac OS X uses OpenGL as the native fast path (for cocoa and X11) */
+    return SDL_TRUE;
+
+#elif defined(__LINUX__)
+    /* Properly configured OpenGL drivers are faster than MIT-SHM */
+#if SDL_VIDEO_OPENGL
+    {
+        static SDL_bool hasAcceleratedOpenGL = HasAcceleratedOpenGL();
+        return hasAcceleratedOpenGL;
+    }
 #elif SDL_VIDEO_OPENGL_ES || SDL_VIDEO_OPENGL_ES2
     /* Let's be optimistic about this! */
     return SDL_TRUE;