Fix trail overlap

code/render/batching.cpp

@@ -439,6 +439,53 @@ void batching_add_quad_internal(primitive_batch* batch, int texture, vertex* ver
 	batch->add_triangle(&v[0], &v[2], &v[3]);
 }
 
+void batching_add_quad_twisted_internal(primitive_batch* batch, int texture, vertex* verts)
+{
+    Assert(batch->get_render_info().prim_type == PRIM_TYPE_TRIS);
+
+    const int NUM_VERTICES = 5;
+    batch_vertex v[NUM_VERTICES];
+
+    auto array_index = texture - batch->get_render_info().texture;
+
+    auto& vertex_center = v[4];
+    vertex_center.tex_coord = vm_vec4_new(0, 0, (float)array_index, 1.0f);
+    vertex_center.position = ZERO_VECTOR;
+    uint16_t center_a = 0, center_r = 0, center_g = 0, center_b = 0;
+
+    for ( int i = 0; i < NUM_VERTICES - 1; i++ ) {
+        v[i].tex_coord = vm_vec4_new(verts[i].texture_position.u, verts[i].texture_position.v, (float)array_index, 1.0f);
+
+        v[i].position = verts[i].world;
+
+        v[i].r = verts[i].r;
+        v[i].g = verts[i].g;
+        v[i].b = verts[i].b;
+        v[i].a = verts[i].a;
+
+        vertex_center.tex_coord.xyzw.x += verts[i].texture_position.u;
+        vertex_center.tex_coord.xyzw.y += verts[i].texture_position.v;
+        vertex_center.position += verts[i].world;
+        center_r += verts[i].r;
+        center_g += verts[i].g;
+        center_b += verts[i].b;
+        center_a += verts[i].a;
+    }
+
+    vertex_center.tex_coord.xyzw.x /= 4.0f;
+    vertex_center.tex_coord.xyzw.y /= 4.0f;
+    vertex_center.position *= 1.0f / 4.0f;
+    vertex_center.r = static_cast<ubyte>(center_r / 4);
+    vertex_center.g = static_cast<ubyte>(center_g / 4);
+    vertex_center.b = static_cast<ubyte>(center_b / 4);
+    vertex_center.a = static_cast<ubyte>(center_a / 4);
+
+    batch->add_triangle(&v[0], &v[1], &v[4]);
+    batch->add_triangle(&v[1], &v[2], &v[4]);
+    batch->add_triangle(&v[2], &v[3], &v[4]);
+    batch->add_triangle(&v[0], &v[4], &v[3]);
+}
+
 void batching_add_tri_internal(primitive_batch *batch, int texture, vertex *verts)
 {
 	Assert(batch->get_render_info().prim_type == PRIM_TYPE_TRIS);
@@ -909,6 +956,17 @@ void batching_add_quad(int texture, vertex *verts, primitive_batch *batch, float
 
 	batching_add_quad_internal(batch, texture, verts, trapezoidal_correction);
 }
+
+void batching_add_quad_twisted(int texture, vertex *verts, primitive_batch *batch)
+{
+    Assertion((texture >= 0), "batching_add_quad() attempted for invalid texture");
+    if ( texture < 0 ) {
+        return;
+    }
+
+    batching_add_quad_twisted_internal(batch, texture, verts);
+}
+
 void batching_add_tri(int texture, vertex *verts)
 {
 	Assertion((texture >= 0), "batching_add_tri() attempted for invalid texture");
@@ -957,6 +1015,7 @@ void batching_render_batch_item(primitive_batch_item* item,
 	} else {
 		batched_bitmap_material material_def;
 
+		material_def.set_cull_mode(item->batch_item_info.mat_type != batch_info::FLAT_EMISSIVE_WITH_BACKFACES);
 		material_set_batched_bitmap(&material_def, item->batch_item_info.texture, 1.0f, 2.0f);
 		gr_render_primitives_batched(&material_def, PRIM_TYPE_TRIS, layout, (int)item->offset, (int)item->n_verts, buffer_num);
 	}

code/render/batching.h

@@ -22,6 +22,7 @@ struct batch_vertex {
 struct batch_info {
 	enum material_type {
 		FLAT_EMISSIVE,
+		FLAT_EMISSIVE_WITH_BACKFACES,
 		VOLUME_EMISSIVE,
 		DISTORTION,
 		FLAT_OPAQUE,
@@ -129,6 +130,7 @@ void batching_add_tri(int texture, vertex *verts);
 
 //these require some blurring the lines between things, but finding the batch in every call gets expensive in some cases such as trails.
 void batching_add_quad(int texture, vertex *verts, primitive_batch* batch, float trapezoidal_correction = 1.0f);
+void batching_add_quad_twisted(int texture, vertex *verts, primitive_batch* batch);
 void batching_add_tri(int texture, vertex *verts, primitive_batch* batch);
 
 void batching_render_all(bool render_distortions = false);

code/weapon/trails.cpp

@@ -149,7 +149,7 @@ void trail_render( trail * trailp )
 		return;
 	}
 
-	auto batchp = batching_find_batch(ti->texture.bitmap_id, batch_info::FLAT_EMISSIVE);
+	auto batchp = batching_find_batch(ti->texture.bitmap_id, batch_info::FLAT_EMISSIVE_WITH_BACKFACES);
 
 	if (trailp->single_segment) {
 		Assertion(trailp->tail == 2, "Single segment trail with more than two values!");
@@ -332,8 +332,12 @@ void trail_render( trail * trailp )
 
 				verts[0].texture_position.v = verts[3].texture_position.v = 0.0f;
 				verts[1].texture_position.v = verts[2].texture_position.v = 1.0f;
-
-				batching_add_quad(ti->texture.bitmap_id, verts, batchp);
+				if (Detail.num_particles == NUM_DEFAULT_DETAIL_LEVELS) {
+					batching_add_quad_twisted(ti->texture.bitmap_id, verts, batchp);
+				} else {
+					batching_add_quad(ti->texture.bitmap_id, verts, batchp);
+				}
+
 			}
 		}