R_Clear: clear stencil buffer together with depth buffer if we have one.

mh suggest that not doing this may cause performance
issues: http://forums.inside3d.com/viewtopic.php?t=2408
It's also mentioned in a "Depth In-Depth" document from AMD.

git-svn-id: svn+ssh://svn.code.sf.net/p/quakespasm/code/trunk@1203 af15c1b1-3010-417e-b628-4374ebc0bcbd

quakespasm/Quake/gl_rmain.c

@@ -489,6 +489,9 @@ void R_Clear (void)
 	unsigned int clearbits;
 
 	clearbits = GL_DEPTH_BUFFER_BIT;
+	// from mh -- if we get a stencil buffer, we should clear it, even though we don't use it
+	if (gl_stencilbits)
+		clearbits |= GL_STENCIL_BUFFER_BIT;
 	if (gl_clear.value)
 		clearbits |= GL_COLOR_BUFFER_BIT;
 	glClear (clearbits);

quakespasm/Quake/gl_vidsdl.c

@@ -104,6 +104,7 @@ qboolean gl_glsl_able = false; //ericw
 GLint gl_max_texture_units = 0; //ericw
 qboolean gl_glsl_gamma_able = false; //ericw
 qboolean gl_glsl_alias_able = false; //ericw
+int gl_stencilbits;
 
 PFNGLMULTITEXCOORD2FARBPROC GL_MTexCoord2fFunc = NULL; //johnfitz
 PFNGLACTIVETEXTUREARBPROC GL_SelectTextureFunc = NULL; //johnfitz
@@ -651,6 +652,10 @@ static qboolean VID_SetMode (int width, int height, int bpp, qboolean fullscreen
 	if (SDL_GL_GetAttribute(SDL_GL_MULTISAMPLESAMPLES, &fsaa_obtained) == -1)
 		fsaa_obtained = 0;
 
+// read stencil bits
+	if (SDL_GL_GetAttribute(SDL_GL_STENCIL_SIZE, &gl_stencilbits) == -1)
+		gl_stencilbits = 0;
+
 	modestate = VID_GetFullscreen() ? MS_FULLSCREEN : MS_WINDOWED;
 
 	CDAudio_Resume ();

quakespasm/Quake/glquake.h

@@ -148,6 +148,8 @@ extern	cvar_t	gl_playermip;
 extern	cvar_t	gl_subdivide_size;
 extern	float	load_subdivide_size; //johnfitz -- remember what subdivide_size value was when this map was loaded
 
+extern int		gl_stencilbits;
+
 // Multitexture
 extern	qboolean	mtexenabled;
 extern	qboolean	gl_mtexable;