DRW: New Select Debug Engine

This is a simple engine used only to debug the texture of select ids.

It is only used when the `WITH_DRAW_DEBUG` option is enabled and the
debug value is 31.

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D5490

6 files changed, 162 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b7dfb56ff02..3baebba4678 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -428,6 +428,10 @@ mark_as_advanced(WITH_CYCLES_NETWORK)
 option(WITH_CUDA_DYNLOAD "Dynamically load CUDA libraries at runtime" ON)
 mark_as_advanced(WITH_CUDA_DYNLOAD)
 
+# Draw Manager
+option(WITH_DRAW_DEBUG "Add extra debug capabilities to Draw Manager" OFF)
+mark_as_advanced(WITH_DRAW_DEBUG)
+
 # LLVM
 option(WITH_LLVM                    "Use LLVM" OFF)
 if(APPLE)
diff --git a/source/blender/blenkernel/BKE_global.h b/source/blender/blenkernel/BKE_global.h
index 69c950a86dc..31928b5e80a 100644
--- a/source/blender/blenkernel/BKE_global.h
+++ b/source/blender/blenkernel/BKE_global.h
@@ -70,6 +70,7 @@ typedef struct Global {
    *   * -16384 and below: Reserved for python (add-ons) usage.
    *   *     -1: Disable faster motion paths computation (since 08/2018).
    *   * 1 - 30: EEVEE debug/stats values (01/2018).
+   *   *     31: Enable the Select Debug Engine. Only available with #WITH_DRAW_DEBUG (08/2021).
    *   *    101: Enable UI debug drawing of fullscreen area's corner widget (10/2014).
    *   *    666: Use quicker batch delete for outliners' delete hierarchy (01/2019).
    *   *    777: Enable UI node panel's sockets polling (11/2011).
diff --git a/source/blender/draw/CMakeLists.txt b/source/blender/draw/CMakeLists.txt
index 930d82fa225..257eb80ae0b 100644
--- a/source/blender/draw/CMakeLists.txt
+++ b/source/blender/draw/CMakeLists.txt
@@ -483,6 +483,13 @@ data_to_c_simple(engines/image/shaders/engine_image_vert.glsl SRC)
 list(APPEND INC
 )
 
+if(WITH_DRAW_DEBUG)
+  list(APPEND SRC
+    engines/select/select_debug_engine.c
+  )
+  add_definitions(-DWITH_DRAW_DEBUG)
+endif()
+
 if(WITH_MOD_FLUID)
   list(APPEND INC
     ../../../intern/mantaflow/extern
diff --git a/source/blender/draw/engines/select/select_debug_engine.c b/source/blender/draw/engines/select/select_debug_engine.c
new file mode 100644
index 00000000000..ded96be23f3
--- /dev/null
+++ b/source/blender/draw/engines/select/select_debug_engine.c
@@ -0,0 +1,135 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * Copyright 2019, Blender Foundation.
+ */
+
+/** \file
+ * \ingroup draw_engine
+ *
+ * Engine for debuging the selection map drawing.
+ */
+
+#include "DNA_ID.h"
+#include "DNA_vec_types.h"
+
+#include "DRW_engine.h"
+#include "DRW_select_buffer.h"
+
+#include "draw_cache.h"
+#include "draw_manager.h"
+
+#include "select_engine.h"
+
+#define SELECT_DEBUG_ENGINE "SELECT_DEBUG_ENGINE"
+
+/* -------------------------------------------------------------------- */
+/** \name Structs and static variables
+ * \{ */
+
+typedef struct SELECTIDDEBUG_PassList {
+  struct DRWPass *debug_pass;
+} SELECTIDDEBUG_PassList;
+
+typedef struct SELECTIDDEBUG_Data {
+  void *engine_type;
+  DRWViewportEmptyList *fbl;
+  DRWViewportEmptyList *txl;
+  SELECTIDDEBUG_PassList *psl;
+  DRWViewportEmptyList *stl;
+} SELECTIDDEBUG_Data;
+
+static struct {
+  struct GPUShader *select_debug_sh;
+} e_data = {{NULL}}; /* Engine data */
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Engine Functions
+ * \{ */
+
+static void select_debug_engine_init(void *vedata)
+{
+  SELECTIDDEBUG_PassList *psl = ((SELECTIDDEBUG_Data *)vedata)->psl;
+
+  if (!e_data.select_debug_sh) {
+    e_data.select_debug_sh = DRW_shader_create_fullscreen(
+        "uniform usampler2D image;"
+        "in vec4 uvcoordsvar;"
+        "out vec4 fragColor;"
+        "void main() {"
+        "  uint px = texture(image, uvcoordsvar.xy).r;"
+        "  fragColor = vec4(1.0, 1.0, 1.0, 0.0);"
+        "  if (px != 0u) {"
+        "    fragColor.a = 1.0;"
+        "    px &= 0x3Fu;"
+        "    fragColor.r = ((px >> 0) & 0x3u) / float(0x3u);"
+        "    fragColor.g = ((px >> 2) & 0x3u) / float(0x3u);"
+        "    fragColor.b = ((px >> 4) & 0x3u) / float(0x3u);"
+        "  }"
+        "}\n",
+        NULL);
+  }
+
+  psl->debug_pass = DRW_pass_create("Debug Pass", DRW_STATE_WRITE_COLOR | DRW_STATE_BLEND_ALPHA);
+  GPUTexture *texture_u32 = DRW_engine_select_texture_get();
+  if (texture_u32) {
+    DRWShadingGroup *shgrp = DRW_shgroup_create(e_data.select_debug_sh, psl->debug_pass);
+    DRW_shgroup_uniform_texture(shgrp, "image", texture_u32);
+    DRW_shgroup_call_procedural_triangles(shgrp, NULL, 1);
+  }
+}
+
+static void select_debug_draw_scene(void *vedata)
+{
+  SELECTIDDEBUG_PassList *psl = ((SELECTIDDEBUG_Data *)vedata)->psl;
+  DRW_draw_pass(psl->debug_pass);
+}
+
+static void select_debug_engine_free(void)
+{
+  DRW_SHADER_FREE_SAFE(e_data.select_debug_sh);
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Engine Type
+ * \{ */
+
+static const DrawEngineDataSize select_debug_data_size = DRW_VIEWPORT_DATA_SIZE(
+    SELECTIDDEBUG_Data);
+
+DrawEngineType draw_engine_debug_select_type = {
+    NULL,
+    NULL,
+    N_("Select ID Debug"),
+    &select_debug_data_size,
+    &select_debug_engine_init,
+    &select_debug_engine_free,
+    NULL,
+    NULL,
+    NULL,
+    &select_debug_draw_scene,
+    NULL,
+    NULL,
+    NULL,
+    NULL,
+};
+
+/** \} */
+
+#undef SELECT_DEBUG_ENGINE
diff --git a/source/blender/draw/engines/select/select_engine.h b/source/blender/draw/engines/select/select_engine.h
index 2b35cf6bee5..d6192103178 100644
--- a/source/blender/draw/engines/select/select_engine.h
+++ b/source/blender/draw/engines/select/select_engine.h
@@ -22,9 +22,15 @@
 
 #pragma once
 
+/* select_engine.c */
 extern DrawEngineType draw_engine_select_type;
 extern RenderEngineType DRW_engine_viewport_select_type;
 
+#ifdef WITH_DRAW_DEBUG
+/* select_debug_engine.c */
+extern DrawEngineType draw_engine_debug_select_type;
+#endif
+
 struct SELECTID_Context *DRW_select_engine_context_get(void);
 
 struct GPUFrameBuffer *DRW_engine_select_framebuffer_get(void);
diff --git a/source/blender/draw/intern/draw_manager.c b/source/blender/draw/intern/draw_manager.c
index 11e2856147f..027ab8ce32b 100644
--- a/source/blender/draw/intern/draw_manager.c
+++ b/source/blender/draw/intern/draw_manager.c
@@ -1281,6 +1281,12 @@ static void drw_engines_enable(ViewLayer *UNUSED(view_layer),
     use_drw_engine(&draw_engine_gpencil_type);
   }
   drw_engines_enable_overlays();
+
+#ifdef WITH_DRAW_DEBUG
+  if (G.debug_value == 31) {
+    use_drw_engine(&draw_engine_debug_select_type);
+  }
+#endif
 }
 
 static void drw_engines_disable(void)
@@ -2940,6 +2946,9 @@ void DRW_engines_register(void)
   DRW_engine_register(&draw_engine_overlay_type);
   DRW_engine_register(&draw_engine_select_type);
   DRW_engine_register(&draw_engine_basic_type);
+#ifdef WITH_DRAW_DEBUG
+  DRW_engine_register(&draw_engine_debug_select_type);
+#endif
 
   DRW_engine_register(&draw_engine_image_type);
   DRW_engine_register(DRW_engine_viewport_external_type.draw_engine);