Avoid shadow geometry artifacts by using hardware depth clamping

Author: BMagnu

code/def_files/data/effects/shadow_map-g.sdr

@@ -42,9 +42,6 @@ void main(void)
 		    gl_Position = shadow_proj_matrix[cascade_id] * gl_in[vert].gl_Position;
 		}
 
-		if(gl_Position.z < -1.0)
-            gl_Position.z = -1.0;
-
 		gl_Layer = cascade_id;
 		gl_ClipDistance[0] = gl_in[vert].gl_ClipDistance[0];
 

code/def_files/data/effects/shadow_map-v.sdr

@@ -82,8 +82,6 @@ void main()
 #ifndef GEOMETRY_FALLBACK
 		int cascade_id = cascade_offset + gl_InstanceID;
         position = shadow_proj_matrix[cascade_id] * position;
-        if(position.z < -1.0)
-        	position.z = -1.0;
 #endif
         gl_Position = position;
     }

code/graphics/opengl/gropengltnl.cpp

@@ -644,7 +644,7 @@ void gr_opengl_render_shadow_draw(gr_buffer_handle ubo_handle, size_t ubo_offset
 
 	GL_state.SetAlphaBlendMode(ALPHA_BLEND_NONE);
 	gr_zbuffer_set(ZBUFFER_TYPE_FULL);
-	gr_set_cull(1);
+	gr_set_cull(0);
 	gr_zbias(-1024);
 	gr_set_fill_mode(GR_FILL_MODE_SOLID);
 	GL_state.ColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
@@ -731,6 +731,8 @@ void gr_opengl_shadow_map_start(matrix4 *shadow_view_matrix, const matrix *light
 
 		glClear(GL_DEPTH_BUFFER_BIT);
 
+		glEnable(GL_DEPTH_CLAMP);
+
 		Glowpoint_override_save = Glowpoint_override;
 		Glowpoint_override = true;
 
@@ -750,6 +752,8 @@ void gr_opengl_shadow_map_end()
 {
 	gr_end_view_matrix();
 
+	glDisable(GL_DEPTH_CLAMP);
+
 	gr_zbuffer_set(ZBUFFER_TYPE_FULL);
 	GL_state.PopFramebufferState();