Overlay: Flash on Mode Transfer overlay

This implements T87633

This overlay renders a flash animation on the target object when
transfering the mode to it using the mode transfer operator.
This provides visual feedback when switching between objects without
extra overlays that affect the general color and lighting in the scene.

Differences with the design task:

- This uses just a fade out animation instead of a fade in/out animation.
The code is ready for fade in/out, but as the rest of the overlays
(face sets, masks...) change instantly without animation, having a fade
in/out effect gives the impression that the object flashes twice (once
for the face sets, twice for the peak alpha of the flash animation).

- The rendering uses a flat color without fresnel for now, but this can
be improved in the future to make it look more like the shader in the
prototype.

- Not enabled by default (can be enabled in the overlays panel), maybe
the defaults can change for 3.0 to disable fade inactive and enable this
instead.

Reviewed By: jbakker, JulienKaspar

Differential Revision: https://developer.blender.org/D11055

3 files changed, 179 insertions, 0 deletions

diff --git a/source/blender/draw/engines/overlay/overlay_engine.c b/source/blender/draw/engines/overlay/overlay_engine.c
index b8f721946f2..19f822e3f68 100644
--- a/source/blender/draw/engines/overlay/overlay_engine.c
+++ b/source/blender/draw/engines/overlay/overlay_engine.c
@@ -207,6 +207,7 @@ static void OVERLAY_cache_init(void *vedata)
   OVERLAY_armature_cache_init(vedata);
   OVERLAY_background_cache_init(vedata);
   OVERLAY_fade_cache_init(vedata);
+  OVERLAY_mode_transfer_cache_init(vedata);
   OVERLAY_extra_cache_init(vedata);
   OVERLAY_facing_cache_init(vedata);
   OVERLAY_gpencil_cache_init(vedata);
@@ -323,6 +324,7 @@ static void OVERLAY_cache_populate(void *vedata, Object *ob)
                            !is_select;
   const bool draw_fade = draw_surface && (pd->overlay.flag & V3D_OVERLAY_FADE_INACTIVE) &&
                          overlay_should_fade_object(ob, draw_ctx->obact);
+  const bool draw_mode_transfer = draw_surface && (pd->overlay.flag & V3D_OVERLAY_MODE_TRANSFER);
   const bool draw_bones = (pd->overlay.flag & V3D_OVERLAY_HIDE_BONES) == 0;
   const bool draw_wires = draw_surface && has_surface &&
                           (pd->wireframe_mode || !pd->hide_overlays);
@@ -349,6 +351,9 @@ static void OVERLAY_cache_populate(void *vedata, Object *ob)
   if (draw_facing) {
     OVERLAY_facing_cache_populate(vedata, ob);
   }
+  if (draw_mode_transfer) {
+    OVERLAY_mode_transfer_cache_populate(vedata, ob);
+  }
   if (draw_wires) {
     OVERLAY_wireframe_cache_populate(vedata, ob, dupli, do_init);
   }
@@ -504,6 +509,7 @@ static void OVERLAY_cache_finish(void *vedata)
         {GPU_ATTACHMENT_TEXTURE(dtxl->depth_in_front), GPU_ATTACHMENT_TEXTURE(dtxl->color)});
   }
 
+  OVERLAY_mode_transfer_cache_finish(vedata);
   OVERLAY_antialiasing_cache_finish(vedata);
   OVERLAY_armature_cache_finish(vedata);
   OVERLAY_image_cache_finish(vedata);
@@ -566,6 +572,7 @@ static void OVERLAY_draw_scene(void *vedata)
   OVERLAY_image_draw(vedata);
   OVERLAY_fade_draw(vedata);
   OVERLAY_facing_draw(vedata);
+  OVERLAY_mode_transfer_draw(vedata);
   OVERLAY_extra_blend_draw(vedata);
   OVERLAY_volume_draw(vedata);
 
@@ -605,6 +612,7 @@ static void OVERLAY_draw_scene(void *vedata)
 
   OVERLAY_fade_infront_draw(vedata);
   OVERLAY_facing_infront_draw(vedata);
+  OVERLAY_mode_transfer_infront_draw(vedata);
 
   if (DRW_state_is_fbo()) {
     GPU_framebuffer_bind(fbl->overlay_line_in_front_fb);
diff --git a/source/blender/draw/engines/overlay/overlay_mode_transfer.c b/source/blender/draw/engines/overlay/overlay_mode_transfer.c
new file mode 100644
index 00000000000..253f606b086
--- /dev/null
+++ b/source/blender/draw/engines/overlay/overlay_mode_transfer.c
@@ -0,0 +1,159 @@
+/*
+ * 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 2021, Blender Foundation.
+ */
+
+/** \file
+ * \ingroup draw_engine
+ */
+
+#include "BKE_paint.h"
+#include "DRW_render.h"
+
+#include "ED_view3d.h"
+
+#include "PIL_time.h"
+#include "UI_resources.h"
+
+#include "overlay_private.h"
+
+void OVERLAY_mode_transfer_cache_init(OVERLAY_Data *vedata)
+{
+  OVERLAY_PassList *psl = vedata->psl;
+  OVERLAY_PrivateData *pd = vedata->stl->pd;
+
+  pd->mode_transfer.time = PIL_check_seconds_timer();
+
+  for (int i = 0; i < 2; i++) {
+    /* Non Meshes Pass (Camera, empties, lights ...) */
+    DRWState state = DRW_STATE_WRITE_COLOR | DRW_STATE_DEPTH_EQUAL | DRW_STATE_BLEND_ALPHA;
+    DRW_PASS_CREATE(psl->mode_transfer_ps[i], state | pd->clipping_state);
+  }
+}
+
+#define MODE_TRANSFER_FLASH_LENGTH 0.55f
+/* TODO(pablodp606): Remove this option for 3.0 if fade in/out is not used. */
+#define MODE_TRANSFER_FLASH_FADE 0.0f
+#define MODE_TRANSFER_FLASH_MAX_ALPHA 0.25f
+
+static bool mode_transfer_is_animation_running(const float anim_time)
+{
+  return anim_time >= 0.0f && anim_time <= MODE_TRANSFER_FLASH_LENGTH;
+}
+
+static float mode_transfer_alpha_for_animation_time_get(const float anim_time)
+{
+  if (anim_time > MODE_TRANSFER_FLASH_LENGTH) {
+    return 0.0f;
+  }
+
+  if (anim_time < 0.0f) {
+    return 0.0f;
+  }
+
+  if (MODE_TRANSFER_FLASH_FADE <= 0.0f) {
+    return (1.0f - (anim_time / MODE_TRANSFER_FLASH_LENGTH)) * MODE_TRANSFER_FLASH_MAX_ALPHA;
+  }
+
+  const float flash_fade_in_time = MODE_TRANSFER_FLASH_LENGTH * MODE_TRANSFER_FLASH_FADE;
+  const float flash_fade_out_time = MODE_TRANSFER_FLASH_LENGTH - flash_fade_in_time;
+
+  float alpha = 0.0f;
+  if (anim_time < flash_fade_in_time) {
+    alpha = anim_time / flash_fade_in_time;
+  }
+  else {
+    const float fade_out_anim_time = anim_time - flash_fade_in_time;
+    alpha = 1.0f - (fade_out_anim_time / flash_fade_out_time);
+  }
+
+  return alpha * MODE_TRANSFER_FLASH_MAX_ALPHA;
+}
+
+void OVERLAY_mode_transfer_cache_populate(OVERLAY_Data *vedata, Object *ob)
+{
+  OVERLAY_PrivateData *pd = vedata->stl->pd;
+  OVERLAY_PassList *psl = vedata->psl;
+
+  if (pd->xray_enabled) {
+    return;
+  }
+
+  const float animation_time = pd->mode_transfer.time -
+                               ob->runtime.overlay_mode_transfer_start_time;
+
+  if (!mode_transfer_is_animation_running(animation_time)) {
+    return;
+  }
+
+  const DRWContextState *draw_ctx = DRW_context_state_get();
+  const bool use_sculpt_pbvh = BKE_sculptsession_use_pbvh_draw(ob, draw_ctx->v3d) &&
+                               !DRW_state_is_image_render();
+  const bool is_xray = (ob->dtx & OB_DRAW_IN_FRONT) != 0;
+
+  DRWShadingGroup *mode_transfer_grp[2];
+
+  for (int i = 0; i < 2; i++) {
+    GPUShader *sh = OVERLAY_shader_uniform_color();
+    mode_transfer_grp[i] = DRW_shgroup_create(sh, psl->mode_transfer_ps[i]);
+    DRW_shgroup_uniform_block(mode_transfer_grp[i], "globalsBlock", G_draw.block_ubo);
+
+    float color[4];
+    UI_GetThemeColor3fv(TH_VERTEX_SELECT, color);
+    color[3] = mode_transfer_alpha_for_animation_time_get(animation_time);
+    srgb_to_linearrgb_v4(color, color);
+    DRW_shgroup_uniform_vec4_copy(mode_transfer_grp[i], "color", color);
+  }
+
+  if (!pd->use_in_front) {
+    mode_transfer_grp[IN_FRONT] = mode_transfer_grp[NOT_IN_FRONT];
+  }
+
+  pd->mode_transfer.any_animated = true;
+
+  if (use_sculpt_pbvh) {
+    DRW_shgroup_call_sculpt(mode_transfer_grp[is_xray], ob, false, false);
+  }
+  else {
+    struct GPUBatch *geom = DRW_cache_object_surface_get(ob);
+    if (geom) {
+      DRW_shgroup_call(mode_transfer_grp[is_xray], geom, ob);
+    }
+  }
+}
+
+void OVERLAY_mode_transfer_draw(OVERLAY_Data *vedata)
+{
+  OVERLAY_PassList *psl = vedata->psl;
+
+  DRW_draw_pass(psl->mode_transfer_ps[NOT_IN_FRONT]);
+}
+
+void OVERLAY_mode_transfer_infront_draw(OVERLAY_Data *vedata)
+{
+  OVERLAY_PassList *psl = vedata->psl;
+
+  DRW_draw_pass(psl->mode_transfer_ps[IN_FRONT]);
+}
+
+void OVERLAY_mode_transfer_cache_finish(OVERLAY_Data *vedata)
+{
+  OVERLAY_PrivateData *pd = vedata->stl->pd;
+  if (pd->mode_transfer.any_animated) {
+    DRW_viewport_request_redraw();
+  }
+  pd->mode_transfer.any_animated = false;
+}
diff --git a/source/blender/draw/engines/overlay/overlay_private.h b/source/blender/draw/engines/overlay/overlay_private.h
index db43136e308..969289a3219 100644
--- a/source/blender/draw/engines/overlay/overlay_private.h
+++ b/source/blender/draw/engines/overlay/overlay_private.h
@@ -107,6 +107,7 @@ typedef struct OVERLAY_PassList {
   DRWPass *gpencil_canvas_ps;
   DRWPass *facing_ps[2];
   DRWPass *fade_ps[2];
+  DRWPass *mode_transfer_ps[2];
   DRWPass *grid_ps;
   DRWPass *image_background_ps;
   DRWPass *image_background_scene_ps;
@@ -282,6 +283,7 @@ typedef struct OVERLAY_PrivateData {
   DRWShadingGroup *extra_grid_grp;
   DRWShadingGroup *facing_grp[2];
   DRWShadingGroup *fade_grp[2];
+  DRWShadingGroup *flash_grp[2];
   DRWShadingGroup *motion_path_lines_grp;
   DRWShadingGroup *motion_path_points_grp;
   DRWShadingGroup *outlines_grp;
@@ -414,6 +416,10 @@ typedef struct OVERLAY_PrivateData {
   struct {
     DRWCallBuffer *handle[2];
   } mball;
+  struct {
+    double time;
+    bool any_animated;
+  } mode_transfer;
 } OVERLAY_PrivateData; /* Transient data */
 
 typedef struct OVERLAY_StorageList {
@@ -607,6 +613,12 @@ void OVERLAY_fade_cache_populate(OVERLAY_Data *vedata, Object *ob);
 void OVERLAY_fade_draw(OVERLAY_Data *vedata);
 void OVERLAY_fade_infront_draw(OVERLAY_Data *vedata);
 
+void OVERLAY_mode_transfer_cache_init(OVERLAY_Data *vedata);
+void OVERLAY_mode_transfer_cache_populate(OVERLAY_Data *vedata, Object *ob);
+void OVERLAY_mode_transfer_draw(OVERLAY_Data *vedata);
+void OVERLAY_mode_transfer_infront_draw(OVERLAY_Data *vedata);
+void OVERLAY_mode_transfer_cache_finish(OVERLAY_Data *vedata);
+
 void OVERLAY_grid_init(OVERLAY_Data *vedata);
 void OVERLAY_grid_cache_init(OVERLAY_Data *vedata);
 void OVERLAY_grid_draw(OVERLAY_Data *vedata);