Fix Bug #23908 - Crash on resize with SDL2.

SDL2 uses shared memory to communicate with the graphics system when
using a software renderer. A resize event will cause SDL2 to
invalidate the SDL_surface that relies on shared memory and any
subsequent calls to will be SDL_GetWindowSurface will cause the shared
memory do be unmapped as the old surface is released.  This is
problematic when it occurs during a rendering cycle, because the
software rendered may also invoke SDL_GetWindowSurface, making any
references to that surface that the game contains become stale. This
will in turn cause a segmentation fault during blitting.

src/events.cpp

@@ -21,6 +21,7 @@
 #include "sound.hpp"
 #include "quit_confirmation.hpp"
 #include "video.hpp"
+#include "display.hpp"
 #if defined _WIN32
 #include "desktop/windows_tray_notification.hpp"
 #endif
@@ -278,7 +279,9 @@ bool has_focus(const sdl_handler* hand, const SDL_Event* event)
 void pump()
 {
 	SDL_PumpEvents();
-
+#if SDL_VERSION_ATLEAST(2,0,0)
+	peek_for_resize();
+#endif
 	pump_info info;
 
 	//used to keep track of double click events
@@ -526,7 +529,7 @@ int pump_info::ticks(unsigned *refresh_counter, unsigned refresh_rate) {
 #if SDL_VERSION_ATLEAST(2,0,0)
 
 /* The constants for the minimum and maximum are picked from the headers. */
-#define INPUT_MIN 0x200
+#define INPUT_MIN 0x300
 #define INPUT_MAX 0x8FF
 
 bool is_input(const SDL_Event& event)
@@ -539,6 +542,19 @@ void discard_input()
 	SDL_FlushEvents(INPUT_MIN, INPUT_MAX);
 }
 
+void peek_for_resize()
+{
+	SDL_Event events[100];
+	int num = SDL_PeepEvents(events, 100, SDL_PEEKEVENT, SDL_WINDOWEVENT, SDL_WINDOWEVENT);
+	for (int i = 0; i < num; i++) {
+		if (events[i].type == SDL_WINDOWEVENT &&
+				events[i].window.event == SDL_WINDOWEVENT_RESIZED) {
+			display::get_singleton()->video().update_framebuffer();
+
+		}
+	}
+}
+
 #else
 
 #define INPUT_MASK (SDL_EVENTMASK(SDL_KEYDOWN)|\

src/events.hpp

@@ -93,6 +93,11 @@ struct event_context
 //causes events to be dispatched to all handler objects.
 void pump();
 
+#if SDL_VERSION_ATLEAST(2,0,0)
+//look for resize events and update references to the screen area
+void peek_for_resize();
+#endif
+
 struct pump_info {
 	pump_info() : resize_dimensions(), ticks_(0) {}
 	std::pair<int,int> resize_dimensions;

src/gui/widgets/grid.cpp

@@ -21,6 +21,9 @@
 #include "gui/auxiliary/layout_exception.hpp"
 #include "gui/widgets/control.hpp"
 #include "utils/foreach.tpp"
+#if SDL_VERSION_ATLEAST(2,0,0)
+#include "events.hpp"
+#endif
 
 #include <numeric>
 
@@ -918,6 +921,10 @@ void tgrid::impl_draw_children(surface& frame_buffer)
 	 * the area not used for resizing the screen, this call `fixes' that.
 	 */
 	SDL_PumpEvents();
+#if SDL_VERSION_ATLEAST(2,0,0)
+	events::peek_for_resize();
+#endif
+
 
 	assert(get_visible() == twidget::tvisible::visible);
 	set_is_dirty(false);
@@ -956,6 +963,9 @@ tgrid::impl_draw_children(surface& frame_buffer, int x_offset, int y_offset)
 	 * the area not used for resizing the screen, this call `fixes' that.
 	 */
 	SDL_PumpEvents();
+#if SDL_VERSION_ATLEAST(2,0,0)
+	events::peek_for_resize();
+#endif
 
 	assert(get_visible() == twidget::tvisible::visible);
 	set_is_dirty(false);

src/hotkey/hotkey_preferences_display.cpp

@@ -598,6 +598,9 @@ void hotkey_preferences_dialog::show_binding_dialog(
 			&& (event.type != SDL_MOUSEBUTTONDOWN )
 	)
 		SDL_PollEvent(&event);
+#if SDL_VERSION_ATLEAST(2,0,0)
+	events::peek_for_resize();
+#endif
 
 	do {
 		switch (event.type) {
@@ -610,6 +613,9 @@ void hotkey_preferences_dialog::show_binding_dialog(
 
 
 		SDL_PollEvent(&event);
+#if SDL_VERSION_ATLEAST(2,0,0)
+	events::peek_for_resize();
+#endif
 		disp_.flip();
 		disp_.delay(10);
 	} while (event.type  != SDL_KEYUP && event.type != SDL_JOYBUTTONUP

src/loadscreen.cpp

@@ -27,6 +27,9 @@
 #include "video.hpp"
 #include "image.hpp"
 #include "text.hpp"
+#if SDL_VERSION_ATLEAST(2,0,0)
+#include "display.hpp"
+#endif
 
 #include <SDL_events.h>
 #include <SDL_image.h>
@@ -206,6 +209,10 @@ void loadscreen::draw_screen(const std::string &text)
 	SDL_Event ev;
 	while(SDL_PollEvent(&ev)) {
 #if SDL_VERSION_ATLEAST(2,0,0)
+		if (ev.type == SDL_WINDOWEVENT &&
+				ev.window.type == SDL_WINDOWEVENT_RESIZED) {
+			display::get_singleton()->video().update_framebuffer();
+		}
 		if (ev.type == SDL_WINDOWEVENT &&
 				(ev.window.type == SDL_WINDOWEVENT_RESIZED ||
 						ev.window.type == SDL_WINDOWEVENT_EXPOSED))

src/video.cpp

@@ -532,6 +532,19 @@ int CVideo::modePossible( int x, int y, int bits_per_pixel, int flags, bool curr
 }
 
 #if SDL_VERSION_ATLEAST(2, 0, 0)
+
+void CVideo::update_framebuffer()
+{
+	if (!window)
+		return;
+
+	surface fb = SDL_GetWindowSurface(*window);
+	if (!frameBuffer)
+		frameBuffer = fb;
+	else
+		frameBuffer.assign(fb);
+}
+
 int CVideo::setMode( int x, int y, int bits_per_pixel, int flags )
 {
 	update_rects.clear();
@@ -554,7 +567,7 @@ int CVideo::setMode( int x, int y, int bits_per_pixel, int flags )
 		}
 	}
 
-	frameBuffer = SDL_GetWindowSurface(*window);
+	update_framebuffer();
 
 	if(frameBuffer != NULL) {
 		image::set_pixel_format(frameBuffer->format);

src/video.hpp

@@ -75,6 +75,11 @@ class CVideo : private boost::noncopyable {
 	int modePossible( int x, int y, int bits_per_pixel, int flags, bool current_screen_optimal=false);
 	int setMode( int x, int y, int bits_per_pixel, int flags );
 
+#if SDL_VERSION_ATLEAST(2, 0, 0)
+	//this needs to be invoked immediately after a resize event or the game will crash.
+	void update_framebuffer();
+#endif
+
 	//did the mode change, since the last call to the modeChanged() method?
 	bool modeChanged();