Refactor glTextureBarrier code into function

Since it's about to be used more times. I named it like
PrepareForSamplingDepthMap instead of something about texture barrier,
because I may want to add more stuff in for #1814 where there is the
possibility to use a copy of the depth texture instead.

Also, always mark depth buffer dirtiness with material system.

Author: slipher

src/engine/renderer/Material.cpp

@@ -2000,6 +2000,11 @@ void MaterialSystem::RenderMaterials( const shaderSort_t fromSort, const shaderS
 		}
 	}
 
+	// All material packs currently render depth-writing shaders.
+	// If we were to render depth fade or anything else sampling u_DepthMap with the material system,
+	// we would need to track this on a per-material basis.
+	backEnd.dirtyDepthBuffer = true;
+
 	GL_BindVAO( backEnd.defaultVAO );
 
 	// Draw the skybox here because we skipped R_AddWorldSurfaces()

src/engine/renderer/tr_backend.cpp

@@ -1210,6 +1210,25 @@ void RB_RunVisTests( )
 	}
 }
 
+void RB_PrepareForSamplingDepthMap()
+{
+	if ( !glConfig.textureBarrierAvailable )
+	{
+		return;
+	}
+
+	if ( !backEnd.dirtyDepthBuffer )
+	{
+		return;
+	}
+
+	// Flush depth buffer to make sure it is available for reading in the depth fade
+	// GLSL - prevents https://github.com/DaemonEngine/Daemon/issues/1676
+	glTextureBarrier();
+
+	backEnd.dirtyDepthBuffer = false;
+}
+
 static void RenderDepthTiles()
 {
 	GL_State( GLS_DEPTHTEST_DISABLE );
@@ -1534,12 +1553,7 @@ void RB_RenderSSAO()
 
 	GLIMP_LOGCOMMENT( "--- RB_RenderSSAO ---" );
 
-	// Assume depth is dirty since we just rendered depth pass and everything opaque
-	if ( glConfig.textureBarrierAvailable )
-	{
-		glTextureBarrier();
-		backEnd.dirtyDepthBuffer = false;
-	}
+	RB_PrepareForSamplingDepthMap();
 
 	GL_State( GLS_DEPTHTEST_DISABLE | GLS_SRCBLEND_DST_COLOR | GLS_DSTBLEND_ZERO );
 	GL_Cull( cullType_t::CT_TWO_SIDED );
@@ -2706,9 +2720,6 @@ static void RB_RenderView( bool depthPass )
 	// draw everything that is translucent
 	if ( glConfig.usingMaterialSystem ) {
 		materialSystem.RenderMaterials( shaderSort_t::SS_ENVIRONMENT_NOFOG, shaderSort_t::SS_POST_PROCESS, backEnd.viewParms.viewID );
-
-		// HACK: assume surfaces with depth fade don't use the material system
-		backEnd.dirtyDepthBuffer = true;
 	}
 	RB_RenderDrawSurfaces( shaderSort_t::SS_ENVIRONMENT_NOFOG, shaderSort_t::SS_POST_PROCESS, DRAWSURFACES_ALL );
 

src/engine/renderer/tr_local.h

@@ -2923,6 +2923,7 @@ void GL_TexImage3D( GLenum target, GLint level, GLint internalFormat, GLsizei wi
 void GL_CompressedTexImage2D( GLenum target, GLint level, GLenum internalformat, GLsizei width, GLsizei height, GLint border, GLsizei imageSize, const void *data, bool isSRGB );
 void GL_CompressedTexSubImage3D( GLenum target, GLint level, GLint xOffset, GLint yOffset, GLint zOffset, GLsizei width, GLsizei height, GLsizei depth, GLenum internalFormat, GLsizei size, const void *data, bool isSRGB );
 	void R_ShutdownBackend();
+	void RB_PrepareForSamplingDepthMap();
 
 	/*
 	====================================================================

src/engine/renderer/tr_shade.cpp

@@ -874,12 +874,9 @@ void Render_generic3D( shaderStage_t *pStage )
 	bool hasDepthFade = pStage->hasDepthFade;
 	bool needDepthMap = pStage->hasDepthFade;
 
-	if ( needDepthMap && backEnd.dirtyDepthBuffer && glConfig.textureBarrierAvailable )
+	if ( needDepthMap )
 	{
-		// Flush depth buffer to make sure it is available for reading in the depth fade
-		// GLSL - prevents https://github.com/DaemonEngine/Daemon/issues/1676
-		glTextureBarrier();
-		backEnd.dirtyDepthBuffer = false;
+		RB_PrepareForSamplingDepthMap();
 	}
 
 	// choose right shader program ----------------------------------