gl1_discardfb functionality expanded

Now also available in GL1. Includes a call to glClear at the beginning
of each frame, pointing to the same buffers that are discarded at the
end. When value is 1, operates over color, depth and stencil buffers.
When it's 2, only does depth and stencil, ignoring color. These
changes provide a performance improvement on mobile/embedded.

doc/040_cvarlist.md

@@ -517,9 +517,10 @@ it's `+set busywait 0` (setting the `busywait` cvar) and `-portable`
   (dynamic lighting) causes slowdown. By default in GL1 is disabled,
   while in GLES1 is enabled. Needs `gl1_multitexture 1` & `vid_restart`.
 
-* **gl1_discardfb**: Only available in ES1. If set to `1` (default),
-  send a hint to discard framebuffers after finishing a frame. Useful
-  for GPUs that attempt to reuse them, something Quake 2 doesn't do.
+* **gl1_discardfb**: If `1`, clear color, depth and stencil buffers at
+  the start of a frame, and discard them at the end if possible. If
+  `2`, do only depth and stencil, no color. Increases performance in
+  mobile / embedded. Default in GL1 is `0`, while in GLES1 is `1`.
 
 
 ## Graphics (OpenGL 3.2 and OpenGL ES3 only)

src/client/refresh/gl1/gl1_main.c

@@ -150,6 +150,7 @@ void LM_FreeLightmapBuffers(void);
 void Scrap_Free(void);
 void Scrap_Init(void);
 
+extern void R_SetDefaultState(void);
 extern void R_ResetGLBuffer(void);
 
 void
@@ -630,6 +631,19 @@ R_PolyBlend(void)
 	glColor4f(1, 1, 1, 1);
 }
 
+static void
+R_ResetClearColor(void)
+{
+	if (gl1_discardfb->value == 1 && !r_clear->value)
+	{
+		glClearColor(0, 0, 0, 0.5);
+	}
+	else
+	{
+		glClearColor(1, 0, 0.5, 0.5);
+	}
+}
+
 void
 R_SetupFrame(void)
 {
@@ -707,7 +721,7 @@ R_SetupFrame(void)
 				vid.height - r_newrefdef.height - r_newrefdef.y,
 				r_newrefdef.width, r_newrefdef.height);
 		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
-		glClearColor(1, 0, 0.5, 0.5);
+		R_ResetClearColor();
 		glDisable(GL_SCISSOR_TEST);
 	}
 }
@@ -857,6 +871,19 @@ R_Clear(void)
 		gldepthmax = 1;
 	}
 
+	switch ((int)gl1_discardfb->value)
+	{
+		case 1:
+			if (gl_state.stereo_mode == STEREO_MODE_NONE)
+			{
+				clearFlags |= GL_COLOR_BUFFER_BIT;
+			}
+		case 2:
+			clearFlags |= GL_STENCIL_BUFFER_BIT;
+		default:
+			break;
+	}
+
 	if (clearFlags)
 	{
 		glClear(clearFlags);
@@ -1183,9 +1210,9 @@ RI_RenderFrame(refdef_t *fd)
 }
 
 #ifdef YQ2_GL1_GLES
-#define DEFAULT_LMCOPIES	"1"
+#define GLES1_ENABLED_ONLY	"1"
 #else
-#define DEFAULT_LMCOPIES	"0"
+#define GLES1_ENABLED_ONLY	"0"
 #endif
 
 void
@@ -1242,10 +1269,8 @@ R_Register(void)
 	gl1_palettedtexture = ri.Cvar_Get("r_palettedtextures", "0", CVAR_ARCHIVE);
 	gl1_pointparameters = ri.Cvar_Get("gl1_pointparameters", "1", CVAR_ARCHIVE);
 	gl1_multitexture = ri.Cvar_Get("gl1_multitexture", "1", CVAR_ARCHIVE);
-	gl1_lightmapcopies = ri.Cvar_Get("gl1_lightmapcopies", DEFAULT_LMCOPIES, CVAR_ARCHIVE);
-#ifdef YQ2_GL1_GLES
-	gl1_discardfb = ri.Cvar_Get("gl1_discardfb", "1", CVAR_ARCHIVE);
-#endif
+	gl1_lightmapcopies = ri.Cvar_Get("gl1_lightmapcopies", GLES1_ENABLED_ONLY, CVAR_ARCHIVE);
+	gl1_discardfb = ri.Cvar_Get("gl1_discardfb", GLES1_ENABLED_ONLY, CVAR_ARCHIVE);
 
 	gl_drawbuffer = ri.Cvar_Get("gl_drawbuffer", "GL_BACK", 0);
 	r_vsync = ri.Cvar_Get("r_vsync", "1", CVAR_ARCHIVE);
@@ -1283,7 +1308,7 @@ R_Register(void)
 	ri.Cmd_AddCommand("gl_strings", R_Strings);
 }
 
-#undef DEFAULT_LMCOPIES
+#undef GLES1_ENABLED_ONLY
 
 /*
  * Changes the video mode
@@ -1687,28 +1712,28 @@ RI_Init(void)
 
 	// ----
 
-	/* Discard framebuffer: Available only on GLES1, enables the use of a "performance hint"
-	 * to the graphic driver, to get rid of the contents of the depth and stencil buffers.
+	/* Discard framebuffer: Enables the use of a "performance hint" to the graphic
+	 * driver in GLES1, to get rid of the contents of the different framebuffers.
 	 * Useful for some GPUs that may attempt to keep them and/or write them back to
 	 * external/uniform memory, actions that are useless for Quake 2 rendering path.
 	 * https://registry.khronos.org/OpenGL/extensions/EXT/EXT_discard_framebuffer.txt
+	 * This extension is used by 'gl1_discardfb', and regardless of its existence,
+	 * that cvar will enable glClear at the start of each frame, helping mobile GPUs.
 	 */
-	gl_config.discardfb = false;
 
 #ifdef YQ2_GL1_GLES
 	R_Printf(PRINT_ALL, " - Discard framebuffer: ");
 
 	if (strstr(gl_config.extensions_string, "GL_EXT_discard_framebuffer"))
 	{
-			qglDiscardFramebufferEXT = (void (APIENTRY *)(GLenum, GLsizei, const GLenum *))
-					RI_GetProcAddress ("glDiscardFramebufferEXT");
+		qglDiscardFramebufferEXT = (void (APIENTRY *)(GLenum, GLsizei, const GLenum *))
+				RI_GetProcAddress ("glDiscardFramebufferEXT");
 	}
 
 	if (gl1_discardfb->value)
 	{
-		if (qglDiscardFramebufferEXT)
+		if (qglDiscardFramebufferEXT)	// enough to verify availability
 		{
-			gl_config.discardfb = true;
 			R_Printf(PRINT_ALL, "Okay\n");
 		}
 		else
@@ -1738,6 +1763,7 @@ RI_Init(void)
 
 	// ----
 
+	R_ResetClearColor();
 	R_SetDefaultState();
 
 	Scrap_Init();
@@ -1970,7 +1996,7 @@ RI_SetPalette(const unsigned char *palette)
 
 	glClearColor(0, 0, 0, 0);
 	glClear(GL_COLOR_BUFFER_BIT);
-	glClearColor(1, 0, 0.5, 0.5);
+	R_ResetClearColor();
 }
 
 /* R_DrawBeam */

src/client/refresh/gl1/gl1_misc.c

@@ -169,7 +169,6 @@ R_Strings(void)
 void
 R_SetDefaultState(void)
 {
-	glClearColor(1, 0, 0.5, 0.5);
 	glDisable(GL_MULTISAMPLE);
 	glCullFace(GL_FRONT);
 	glEnable(GL_TEXTURE_2D);

src/client/refresh/gl1/gl1_sdl.c

@@ -38,6 +38,8 @@ static SDL_GLContext context = NULL;
 qboolean IsHighDPIaware = false;
 static qboolean vsyncActive = false;
 
+extern cvar_t *gl1_discardfb;
+
 // ----
 
 /*
@@ -47,13 +49,26 @@ void
 RI_EndFrame(void)
 {
 	R_ApplyGLBuffer();	// to draw buffered 2D text
+
 #ifdef YQ2_GL1_GLES
-	if (gl_config.discardfb)
+	static const GLenum attachments[3] = {GL_COLOR_EXT, GL_DEPTH_EXT, GL_STENCIL_EXT};
+
+	if (qglDiscardFramebufferEXT)
 	{
-		static const GLenum attachments[] = { GL_DEPTH_EXT, GL_STENCIL_EXT };
-		qglDiscardFramebufferEXT(GL_FRAMEBUFFER_OES, 2, attachments);
+		switch ((int)gl1_discardfb->value)
+		{
+			case 1:
+				qglDiscardFramebufferEXT(GL_FRAMEBUFFER_OES, 3, &attachments[0]);
+				break;
+			case 2:
+				qglDiscardFramebufferEXT(GL_FRAMEBUFFER_OES, 2, &attachments[1]);
+				break;
+			default:
+				break;
+		}
 	}
 #endif
+
 	SDL_GL_SwapWindow(window);
 }
 

src/client/refresh/gl1/header/local.h

@@ -148,8 +148,6 @@ typedef struct	//	832k aprox.
 
 #include "model.h"
 
-void R_SetDefaultState(void);
-
 extern glbuffer_t gl_buf;
 extern float gldepthmin, gldepthmax;
 
@@ -427,7 +425,6 @@ typedef struct
 	qboolean pointparameters;
 	qboolean multitexture;
 	qboolean lightmapcopies;	// many copies of same lightmap, for embedded
-	qboolean discardfb;
 
 	// ----