Ignore depth draw optimization when using depth draw alpha prepass

This is necessary as the scene shader still uses alpha in this case so we can't discard fragments that weren't written to the depth buffer

3 files changed, 8 insertions, 7 deletions

diff --git a/servers/rendering/renderer_rd/forward_clustered/render_forward_clustered.cpp b/servers/rendering/renderer_rd/forward_clustered/render_forward_clustered.cpp
index 5b465fb45c..bcee7315c8 100644
--- a/servers/rendering/renderer_rd/forward_clustered/render_forward_clustered.cpp
+++ b/servers/rendering/renderer_rd/forward_clustered/render_forward_clustered.cpp
@@ -3465,7 +3465,7 @@ void RenderForwardClustered::_geometry_instance_add_surface_with_material(Geomet
 	if (has_alpha || has_read_screen_alpha || p_material->shader_data->depth_draw == SceneShaderForwardClustered::ShaderData::DEPTH_DRAW_DISABLED || p_material->shader_data->depth_test == SceneShaderForwardClustered::ShaderData::DEPTH_TEST_DISABLED) {
 		//material is only meant for alpha pass
 		flags |= GeometryInstanceSurfaceDataCache::FLAG_PASS_ALPHA;
-		if (p_material->shader_data->uses_depth_pre_pass && !(p_material->shader_data->depth_draw == SceneShaderForwardClustered::ShaderData::DEPTH_DRAW_DISABLED || p_material->shader_data->depth_test == SceneShaderForwardClustered::ShaderData::DEPTH_TEST_DISABLED)) {
+		if (p_material->shader_data->uses_depth_prepass_alpha && !(p_material->shader_data->depth_draw == SceneShaderForwardClustered::ShaderData::DEPTH_DRAW_DISABLED || p_material->shader_data->depth_test == SceneShaderForwardClustered::ShaderData::DEPTH_TEST_DISABLED)) {
 			flags |= GeometryInstanceSurfaceDataCache::FLAG_PASS_DEPTH;
 			flags |= GeometryInstanceSurfaceDataCache::FLAG_PASS_SHADOW;
 		}
@@ -3481,7 +3481,7 @@ void RenderForwardClustered::_geometry_instance_add_surface_with_material(Geomet
 
 	SceneShaderForwardClustered::MaterialData *material_shadow = nullptr;
 	void *surface_shadow = nullptr;
-	if (!p_material->shader_data->uses_particle_trails && !p_material->shader_data->writes_modelview_or_projection && !p_material->shader_data->uses_vertex && !p_material->shader_data->uses_position && !p_material->shader_data->uses_discard && !p_material->shader_data->uses_depth_pre_pass && !p_material->shader_data->uses_alpha_clip && p_material->shader_data->cull_mode == SceneShaderForwardClustered::ShaderData::CULL_BACK && !p_material->shader_data->uses_point_size) {
+	if (!p_material->shader_data->uses_particle_trails && !p_material->shader_data->writes_modelview_or_projection && !p_material->shader_data->uses_vertex && !p_material->shader_data->uses_position && !p_material->shader_data->uses_discard && !p_material->shader_data->uses_depth_prepass_alpha && !p_material->shader_data->uses_alpha_clip && p_material->shader_data->cull_mode == SceneShaderForwardClustered::ShaderData::CULL_BACK && !p_material->shader_data->uses_point_size) {
 		flags |= GeometryInstanceSurfaceDataCache::FLAG_USES_SHARED_SHADOW_MATERIAL;
 		material_shadow = static_cast<SceneShaderForwardClustered::MaterialData *>(RendererRD::MaterialStorage::get_singleton()->material_get_data(scene_shader.default_material, RendererRD::MaterialStorage::SHADER_TYPE_3D));
 
diff --git a/servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.cpp b/servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.cpp
index 914ca25899..9074a23472 100644
--- a/servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.cpp
+++ b/servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.cpp
@@ -61,7 +61,7 @@ void SceneShaderForwardClustered::ShaderData::set_code(const String &p_code) {
 	uses_alpha = false;
 	uses_alpha_clip = false;
 	uses_blend_alpha = false;
-	uses_depth_pre_pass = false;
+	uses_depth_prepass_alpha = false;
 	uses_discard = false;
 	uses_roughness = false;
 	uses_normal = false;
@@ -114,7 +114,7 @@ void SceneShaderForwardClustered::ShaderData::set_code(const String &p_code) {
 	// Use alpha clip pipeline for alpha hash/dither.
 	// This prevents sorting issues inherent to alpha blending and allows such materials to cast shadows.
 	actions.usage_flag_pointers["ALPHA_HASH_SCALE"] = &uses_alpha_clip;
-	actions.render_mode_flags["depth_prepass_alpha"] = &uses_depth_pre_pass;
+	actions.render_mode_flags["depth_prepass_alpha"] = &uses_depth_prepass_alpha;
 
 	actions.usage_flag_pointers["SSS_STRENGTH"] = &uses_sss;
 	actions.usage_flag_pointers["SSS_TRANSMITTANCE_DEPTH"] = &uses_transmittance;
@@ -309,10 +309,11 @@ void SceneShaderForwardClustered::ShaderData::set_code(const String &p_code) {
 						}
 
 						RD::PipelineDepthStencilState depth_stencil = depth_stencil_state;
-						if (depth_pre_pass_enabled && casts_shadows()) {
+						if (depth_pre_pass_enabled && casts_shadows() && !uses_depth_prepass_alpha) {
 							// We already have a depth from the depth pre-pass, there is no need to write it again.
 							// In addition we can use COMPARE_OP_EQUAL instead of COMPARE_OP_LESS_OR_EQUAL.
 							// This way we can use the early depth test to discard transparent fragments before the fragment shader even starts.
+							// This cannot be used with depth_prepass_alpha as it uses a different threshold during the depth-prepass and regular drawing.
 							depth_stencil.depth_compare_operator = RD::COMPARE_OP_EQUAL;
 							depth_stencil.enable_depth_write = false;
 						}
@@ -394,7 +395,7 @@ bool SceneShaderForwardClustered::ShaderData::casts_shadows() const {
 	bool has_base_alpha = (uses_alpha && !uses_alpha_clip) || has_read_screen_alpha;
 	bool has_alpha = has_base_alpha || uses_blend_alpha;
 
-	return !has_alpha || (uses_depth_pre_pass && !(depth_draw == DEPTH_DRAW_DISABLED || depth_test == DEPTH_TEST_DISABLED));
+	return !has_alpha || (uses_depth_prepass_alpha && !(depth_draw == DEPTH_DRAW_DISABLED || depth_test == DEPTH_TEST_DISABLED));
 }
 
 RS::ShaderNativeSourceCode SceneShaderForwardClustered::ShaderData::get_native_source_code() const {
diff --git a/servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.h b/servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.h
index 51e4dd44d5..367f44f50c 100644
--- a/servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.h
+++ b/servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.h
@@ -153,7 +153,7 @@ public:
 		bool uses_alpha = false;
 		bool uses_blend_alpha = false;
 		bool uses_alpha_clip = false;
-		bool uses_depth_pre_pass = false;
+		bool uses_depth_prepass_alpha = false;
 		bool uses_discard = false;
 		bool uses_roughness = false;
 		bool uses_normal = false;