Metal: First set of Geometry Shader alternative implementations using SSBO vertex shader fetch.

These implementations remove dependency on the Geometry pass by instead invoking one vertex shader instance for each expected output vertex, matching what a geometry shader would emit. Each vertex shader instance is then responsible for calculating the same output position based on its vertex_id as the logic would in the geometry shader version.

SSBO Vertex fetch enables full random-access into a vertex buffer by binding it as a read-only SSBO. This enables each instance to read neighbouring vertex data to perform contextual calculations as a geometry shader would, for cases where attribute Multiload is not supported.

Authored by Apple: Michael Parkin-White

Ref T96261

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D15901

1 files changed, 25 insertions, 0 deletions

diff --git a/source/blender/gpu/intern/gpu_shader_create_info.cc b/source/blender/gpu/intern/gpu_shader_create_info.cc
index a18fdcd32df..ff7aa65f03f 100644
--- a/source/blender/gpu/intern/gpu_shader_create_info.cc
+++ b/source/blender/gpu/intern/gpu_shader_create_info.cc
@@ -305,6 +305,31 @@ void gpu_shader_create_info_init()
     draw_resource_id_new = draw_resource_id_fallback;
   }
 
+  /* Metal-specific alternatives for Geometry shaders. */
+  if (GPU_type_matches_ex(GPU_DEVICE_ANY, GPU_OS_MAC, GPU_DRIVER_ANY, GPU_BACKEND_METAL)) {
+
+    /* 3D polyline. */
+    gpu_shader_3D_polyline_uniform_color = gpu_shader_3D_polyline_uniform_color_no_geom;
+    gpu_shader_3D_polyline_flat_color = gpu_shader_3D_polyline_flat_color_no_geom;
+    gpu_shader_3D_polyline_smooth_color = gpu_shader_3D_polyline_smooth_color_no_geom;
+    gpu_shader_3D_polyline_uniform_color_clipped =
+        gpu_shader_3D_polyline_uniform_color_clipped_no_geom;
+
+    /* Overlay Edit Mesh. */
+    overlay_edit_mesh_edge = overlay_edit_mesh_edge_no_geom;
+    overlay_edit_mesh_edge_flat = overlay_edit_mesh_edge_flat_no_geom;
+    overlay_edit_mesh_edge_clipped = overlay_edit_mesh_edge_clipped_no_geom;
+    overlay_edit_mesh_edge_flat_clipped = overlay_edit_mesh_edge_flat_clipped_no_geom;
+
+    /* Overlay Armature Shape outline. */
+    overlay_armature_shape_outline = overlay_armature_shape_outline_no_geom;
+    overlay_armature_shape_outline_clipped = overlay_armature_shape_outline_clipped_no_geom;
+
+    /* Overlay Motion Path Line. */
+    overlay_motion_path_line = overlay_motion_path_line_no_geom;
+    overlay_motion_path_line_clipped = overlay_motion_path_line_clipped_no_geom;
+  }
+
   for (ShaderCreateInfo *info : g_create_infos->values()) {
     if (info->do_static_compilation_) {
       info->builtins_ |= gpu_shader_dependency_get_builtins(info->vertex_source_);