source/blender/compositor/realtime_compositor/CMakeLists.txt

@@ -118,6 +118,7 @@ set(GLSL_SRC
   shaders/compositor_glare_simple_star_vertical_pass.glsl
   shaders/compositor_glare_streaks_accumulate.glsl
   shaders/compositor_glare_streaks_filter.glsl
+  shaders/compositor_id_mask.glsl
   shaders/compositor_image_crop.glsl
   shaders/compositor_map_uv.glsl
   shaders/compositor_morphological_distance.glsl
@@ -215,6 +216,7 @@ set(SRC_SHADER_CREATE_INFOS
   shaders/infos/compositor_filter_info.hh
   shaders/infos/compositor_flip_info.hh
   shaders/infos/compositor_glare_info.hh
+  shaders/infos/compositor_id_mask_info.hh
   shaders/infos/compositor_image_crop_info.hh
   shaders/infos/compositor_map_uv_info.hh
   shaders/infos/compositor_morphological_distance_feather_info.hh

source/blender/compositor/realtime_compositor/shaders/compositor_id_mask.glsl

@@ -0,0 +1,11 @@
+#pragma BLENDER_REQUIRE(gpu_shader_compositor_texture_utilities.glsl)
+
+void main()
+{
+  ivec2 texel = ivec2(gl_GlobalInvocationID.xy);
+
+  float input_mask_value = texture_load(input_mask_tx, texel).x;
+  float mask = int(round(input_mask_value)) == index ? 1.0 : 0.0;
+
+  imageStore(output_mask_img, texel, vec4(mask));
+}

source/blender/compositor/realtime_compositor/shaders/infos/compositor_id_mask_info.hh

@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "gpu_shader_create_info.hh"
+
+GPU_SHADER_CREATE_INFO(compositor_id_mask)
+    .local_group_size(16, 16)
+    .push_constant(Type::INT, "index")
+    .sampler(0, ImageType::FLOAT_2D, "input_mask_tx")
+    .image(0, GPU_R16F, Qualifier::WRITE, ImageType::FLOAT_2D, "output_mask_img")
+    .compute_source("compositor_id_mask.glsl")
+    .do_static_compilation(true);

source/blender/nodes/composite/nodes/node_composite_id_mask.cc

@@ -5,11 +5,16 @@
  * \ingroup cmpnodes
  */
 
+#include <cmath>
+
 #include "BLT_translation.h"
 
 #include "UI_interface.h"
 #include "UI_resources.h"
 
+#include "GPU_shader.h"
+
+#include "COM_algorithm_smaa.hh"
 #include "COM_node_operation.hh"
 
 #include "node_composite_util.hh"
@@ -20,7 +25,11 @@ namespace blender::nodes::node_composite_id_mask_cc {
 
 static void cmp_node_idmask_declare(NodeDeclarationBuilder &b)
 {
-  b.add_input<decl::Float>(N_("ID value")).default_value(1.0f).min(0.0f).max(1.0f);
+  b.add_input<decl::Float>(N_("ID value"))
+      .default_value(1.0f)
+      .min(0.0f)
+      .max(1.0f)
+      .compositor_domain_priority(0);
   b.add_output<decl::Float>(N_("Alpha"));
 }
 
@@ -38,8 +47,56 @@ class IDMaskOperation : public NodeOperation {
 
   void execute() override
   {
-    get_input("ID value").pass_through(get_result("Alpha"));
-    context().set_info_message("Viewport compositor setup not fully supported");
+    const Result &input_mask = get_input("ID value");
+    if (input_mask.is_single_value()) {
+      execute_single_value();
+      return;
+    }
+
+    GPUShader *shader = shader_manager().get("compositor_id_mask");
+    GPU_shader_bind(shader);
+
+    GPU_shader_uniform_1i(shader, "index", get_index());
+
+    input_mask.bind_as_texture(shader, "input_mask_tx");
+
+    /* If anti-aliasing is disabled, write to the output directly, otherwise, write to a temporary
+     * result to later perform anti-aliasing. */
+    Result non_anti_aliased_mask = Result::Temporary(ResultType::Float, texture_pool());
+    Result &output_mask = use_anti_aliasing() ? non_anti_aliased_mask : get_result("Alpha");
+
+    const Domain domain = compute_domain();
+    output_mask.allocate_texture(domain);
+    output_mask.bind_as_image(shader, "output_mask_img");
+
+    compute_dispatch_threads_at_least(shader, domain.size);
+
+    input_mask.unbind_as_texture();
+    output_mask.unbind_as_image();
+    GPU_shader_unbind();
+
+    if (use_anti_aliasing()) {
+      smaa(context(), non_anti_aliased_mask, get_result("Alpha"));
+      non_anti_aliased_mask.release();
+    }
+  }
+
+  void execute_single_value()
+  {
+    const float input_mask_value = get_input("ID value").get_float_value();
+    const float mask = int(round(input_mask_value)) == get_index() ? 1.0f : 0.0f;
+    get_result("Alpha").allocate_single_value();
+    get_result("Alpha").set_float_value(mask);
+  }
+
+  int get_index()
+  {
+    return bnode().custom1;
+  }
+
+  bool use_anti_aliasing()
+  {
+    return bnode().custom2 != 0;
   }
 };
 
@@ -60,8 +117,6 @@ void register_node_type_cmp_idmask()
   ntype.declare = file_ns::cmp_node_idmask_declare;
   ntype.draw_buttons = file_ns::node_composit_buts_id_mask;
   ntype.get_compositor_operation = file_ns::get_compositor_operation;
-  ntype.realtime_compositor_unsupported_message = N_(
-      "Node not supported in the Viewport compositor");
 
   nodeRegisterType(&ntype);
 }