[rend2] Make sky ignore prepass depth

Mappers use blended depthwritten occluders to mask map geometry and still want to see the sky behind them. Only use depthtest for skies when there was something written to the image before the skydraw like portals or skyportals.

Author: SomaZ

shared/rd-rend2/tr_backend.cpp

@@ -1549,6 +1549,9 @@ static void RB_RenderDrawSurfList( drawSurf_t *drawSurfs, int numDrawSurfs )
 	backEnd.refdef.floatTime = originalTime;
 	FBO_Bind(fbo);
 	GL_SetModelviewMatrix(backEnd.viewParms.world.modelViewMatrix);
+
+	if (backEnd.viewParms.viewParmType == VPT_PORTAL || backEnd.viewParms.viewParmType == VPT_SKYPORTAL)
+		tr.portalRenderedThisFrame = qtrue;
 }
 
 

shared/rd-rend2/tr_local.h

@@ -2686,6 +2686,7 @@ typedef struct trGlobals_s {
 	viewParms_t				viewParms;
 	viewParms_t				cachedViewParms[3 + MAX_DLIGHTS * 6 + 3 + MAX_DRAWN_PSHADOWS];
 	int						numCachedViewParms;
+	qboolean				portalRenderedThisFrame;
 
 	viewParms_t				skyPortalParms;
 	byte					skyPortalAreaMask[MAX_MAP_AREA_BYTES];

shared/rd-rend2/tr_scene.cpp

@@ -503,6 +503,7 @@ void RE_BeginScene(const refdef_t *fd)
 	// each scene / view.
 	tr.frameSceneNum++;
 	tr.sceneCount++;
+	tr.portalRenderedThisFrame = qfalse;
 
 	//ri.Printf(PRINT_ALL, "RE_BeginScene Frame: %i, skyportal: %i, entities: %i\n", backEndData->realFrameNumber, int(tr.world->skyboxportal && (tr.refdef.rdflags & RDF_SKYBOXPORTAL)), tr.refdef.num_entities);
 	R_GatherFrameViews(&tr.refdef);

shared/rd-rend2/tr_sky.cpp

@@ -464,6 +464,7 @@ static void DrawSkySide( struct image_s *image, const int mins[2], const int max
 	};
 
 	DrawItem item = {};
+	item.renderState.stateBits = tr.portalRenderedThisFrame ? 0 : GLS_DEPTHTEST_DISABLE;
 	item.renderState.cullType = CT_TWO_SIDED;
 	item.renderState.depthRange = RB_GetDepthRange(backEnd.currentEntity, tess.shader);
 	item.program = sp;