SDL3: Handle r_fillWindowAlphaChan, cleanups and comments

r_fillWindowAlphaChan is a hack to work around an older issue with
Wayland/Mesa, which has been fixed in Mesa 24.1 (and also seems to work
with current NVIDIA drivers). Additionally, in SDL3 the EGL-specific
(and thus mostly only affecting Wayland)
SDL_HINT_VIDEO_EGL_ALLOW_TRANSPARENCY has been replaced with the generic
SDL_PROP_WINDOW_CREATE_TRANSPARENT_BOOLEAN (that could also affect
other platforms), so it's harder to enable this only for Wayland.
I think most people using SDL3 will use a recent Mesa/driver versions,
so I don't enable it by default for SDL3 (SDL2 behaves like before).
However, with `r_fillWindowAlphaChan 1` the hack can be enabled anyway
(r_fillWindowAlphaChan defaults to "-1" which means "let dhewm3 decide
 whether to enable this")

neo/renderer/tr_backend.cpp

@@ -30,7 +30,7 @@ If you have questions concerning this license or the applicable additional terms
 
 #include "renderer/tr_local.h"
 
-static idCVar r_fillWindowAlphaChan( "r_fillWindowAlphaChan", "-1", CVAR_SYSTEM | CVAR_NOCHEAT | CVAR_ARCHIVE, "Make sure alpha channel of windows default framebuffer is completely opaque at the end of each frame. Needed at least when using Wayland.\n 1: do this, 0: don't do it, -1: let dhewm3 decide (default)" );
+static idCVar r_fillWindowAlphaChan( "r_fillWindowAlphaChan", "-1", CVAR_SYSTEM | CVAR_NOCHEAT | CVAR_ARCHIVE, "Make sure alpha channel of windows default framebuffer is completely opaque at the end of each frame. Needed at least when using Wayland with older drivers.\n 1: do this, 0: don't do it, -1: let dhewm3 decide (default)" );
 
 frameData_t		*frameData;
 backEndState_t	backEnd;

neo/renderer/tr_local.h

@@ -1073,7 +1073,7 @@ typedef struct {
 	bool		fullScreen;
 	bool		fullScreenDesktop;
 	bool		stereo;
-	int			displayHz;
+	int			displayHz; // TODO: SDL3 uses float
 	int			multiSamples;
 } glimpParms_t;
 

neo/sys/cpu.cpp

@@ -30,9 +30,6 @@ If you have questions concerning this license or the applicable additional terms
 
 #ifdef D3_SDL3
   #include <SDL3/SDL_cpuinfo.h>
-  // in SDL3, SDL_Has3DNow() has been removed, and nowadays it's not really relevant anyway,
-  // so just replace it with 0/false
-  #define SDL_Has3DNow() 0
 #else // SDL1.2 or SDL2
   #include <SDL_cpuinfo.h>
 #endif
@@ -208,8 +205,11 @@ int Sys_GetProcessorId( void ) {
 	if (SDL_HasMMX())
 		flags |= CPUID_MMX;
 
+	// SDL3 doesn't support detecting 3DNow, and current CPUs (even from AMD) don't support it either
+#ifndef D3_SDL3
 	if (SDL_Has3DNow())
 		flags |= CPUID_3DNOW;
+#endif
 
 	if (SDL_HasSSE())
 		flags |= CPUID_SSE;

neo/sys/events.cpp

@@ -152,8 +152,6 @@ If you have questions concerning this license or the applicable additional terms
 
   #define IS_SDL_BTN_DOWN(EV)  EV.down
 
-  // FIXME: at some point I need to enable (and possibly later disable) SDL_TextInput!
-
 #else // SDL2 and SDL1.2
 
   #define IS_SDL_BTN_DOWN(EV)  (EV.state == SDL_PRESSED)
@@ -1209,7 +1207,9 @@ sysEvent_t Sys_GetEvent() {
 	}
 
 #if SDL_VERSION_ATLEAST(2, 0, 0)
-	// s used to have SDL_TEXTINPUTEVENT_TEXT_SIZE (32) bytes, but in SDL3 the string can have
+	// s holds the string from the last SDL_TEXTINPUT event, to generate SE_CHARS D3 events,
+	// one event per call to this function until all chars have been handled
+	// it used to have SDL_TEXTINPUTEVENT_TEXT_SIZE (32) bytes, but in SDL3 the string can have
 	// arbitrary size, however I assume that 128 should still be more than enough
 	static char s[128] = {0};
 	static size_t s_pos = 0;
@@ -1229,6 +1229,9 @@ sysEvent_t Sys_GetEvent() {
 	}
 #endif
 
+	// c holds a single char for a SE_CHAR event, probably coming from a SDL_KEYDOWN event
+	// (that was also returned as SE_KEY), or from a SDL_TEXTINPUT event that contained just one char.
+	// It's 0 when not currently holding a char to generate an event
 	static byte c = 0;
 
 	if (c) {
@@ -1421,6 +1424,7 @@ sysEvent_t Sys_GetEvent() {
 			if (ev.key.state == SDL_PRESSED && (ev.key.keysym.unicode & 0xff00) == 0)
 				c = ev.key.keysym.unicode & 0xff;
 #endif
+			// Note: c will be sent as SE_CHAR next time this function is called
 
 			return res;
 
@@ -1440,7 +1444,9 @@ sysEvent_t Sys_GetEvent() {
 						memcpy( s, ev.text.text, SDL_TEXTINPUTEVENT_TEXT_SIZE );
 						s[SDL_TEXTINPUTEVENT_TEXT_SIZE] = '\0';
 	#endif
-						s_pos = 1; // pos 0 is returned
+						// pos 0 is returned, the rest of s is returned as SE_CHAR events
+						// at the next times this function is called
+						s_pos = 1;
 					}
 					return res;
 				} else if( D3_UTF8toISO8859_1( ev.text.text, s, sizeof(s) ) && s[0] != '\0' ) {
@@ -1449,7 +1455,9 @@ sysEvent_t Sys_GetEvent() {
 						s_pos = 0;
 						s[0] = '\0';
 					} else {
-						s_pos = 1; // pos 0 is returned
+						// pos 0 is returned, the rest of s is returned as SE_CHAR events
+						// at the next times this function is called
+						s_pos = 1;
 					}
 					return res;
 				}

neo/sys/glimp.cpp

@@ -219,20 +219,25 @@ bool GLimp_Init(glimpParms_t parms) {
 	 * rendering bugs (the window is partly transparent or very white in areas with low alpha).
 	 * Mesa introduced an EGL extension that's supposed to fix that (EGL_EXT_present_opaque)
 	 * and newer SDL2 versions use it by default (in the Wayland backend).
-	 * Unfortunately, the implementation of that extension is (currently?) broken (at least
-	 * in Mesa), seems like they just give you a visual without any alpha chan - which doesn't
+	 * Unfortunately, the implementation of that extension was broken (at least in Mesa before 24.1),
+	 * seems like they just give you a visual without any alpha chan - which doesn't
 	 * work for Doom3, as it needs a functioning alpha chan for blending operations, see above.
 	 * See also: https://gitlab.freedesktop.org/mesa/mesa/-/issues/5886
 	 *
 	 * So to make sure dhewm3 (finally) works as expected on Wayland, we tell SDL2 to
 	 * allow transparency and then fill the alpha-chan ourselves in RB_SwapBuffers()
-	 * (unless the user disables that with r_fillWindowAlphaChan 0) */
+	 * (unless the user disables that with r_fillWindowAlphaChan 0)
+	 *
+	 * NOTE: This bug is fixed in Mesa 24.1 and newer, and doesn't seem to occur with recent
+	 *       NVIDIA drivers either, so for SDL3 (which should be mostly used with current drivers/mesa)
+	 *       I don't enable this hack by default. If r_fillWindowAlphaChan == 1, it's enabled
+	 *       when creating the window, though.
+	 */
   #ifdef SDL_HINT_VIDEO_EGL_ALLOW_TRANSPARENCY
 	SDL_SetHint(SDL_HINT_VIDEO_EGL_ALLOW_TRANSPARENCY, "1");
   #elif SDL_MAJOR_VERSION == 2 // little hack so this works if the SDL2 version used for building is older than runtime version
 	SDL_SetHint("SDL_VIDEO_EGL_ALLOW_TRANSPARENCY", "1");
   #endif
-	// Note: for SDL3 we use SDL_PROP_WINDOW_CREATE_TRANSPARENT_BOOLEAN below
 #endif
 
 	int colorbits = 24;
@@ -401,15 +406,17 @@ bool GLimp_Init(glimpParms_t parms) {
 		SDL_SetNumberProperty(props, SDL_PROP_WINDOW_CREATE_WIDTH_NUMBER, parms.width);
 		SDL_SetNumberProperty(props, SDL_PROP_WINDOW_CREATE_HEIGHT_NUMBER, parms.height);
 		SDL_SetNumberProperty(props, SDL_PROP_WINDOW_CREATE_FLAGS_NUMBER, flags);
-		// TODO: the following is probably redundant with the flag already set
-		//if ( parms.fullScreen && parms.fullScreenDesktop ) {
-		//	SDL_SetBooleanProperty(props, SDL_PROP_WINDOW_CREATE_FULLSCREEN_BOOLEAN, true);
-		//} // for exclusive fullscreen, create in windowed mode first, need to call
 
-		// TODO: SDL_SetBooleanProperty(props, SDL_PROP_WINDOW_CREATE_TRANSPARENT_BOOLEAN, true);
-		//       as replacement for SDL_VIDEO_EGL_ALLOW_TRANSPARENCY - but when?
-		//       I don't want this on all platforms.. but can I already detect wayland at this point?
-		//   Also: recent mesa versions should have this fixed, so maybe ignore the issue for SDL3? what about nvidia?
+		// See above for the big comment about Wayland and alpha channels.
+		// When using SDL3 I assume that people usually won't be affected by this bug,
+		// because it's fixed in recent Mesa versions (and also works with the NVIDIA driver).
+		// However, with `r_fillWindowAlphaChan 1` its usage can still be enforced
+		// on Unix-like platforms (I don't think there's a point in this on Windows or Mac)
+	  #if defined(__unix__) && !defined(__APPLE__)
+		if ( cvarSystem->GetCVarInteger( "r_fillWindowAlphaChan" ) == 1 ) {
+			SDL_SetBooleanProperty(props, SDL_PROP_WINDOW_CREATE_TRANSPARENT_BOOLEAN, true);
+		}
+	  #endif
 
 		window = SDL_CreateWindowWithProperties(props);
 		SDL_DestroyProperties(props);
@@ -753,7 +760,9 @@ bool GLimp_Init(glimpParms_t parms) {
 #if SDL_VERSION_ATLEAST(2, 0, 0)
 		const char* videoDriver = SDL_GetCurrentVideoDriver();
 		if (idStr::Icmp(videoDriver, "wayland") == 0) {
+	#if SDL_MAJOR_VERSION == 2 // don't enable this hack by default with SDL3
 			glConfig.shouldFillWindowAlpha = true;
+	#endif
 			glConfig.isWayland = true;
 		}
 #endif