Curves: Add sculpt selection overlay

This commit adds visualization to the selection in curves sculpt mode.
Previously it was only possible to see the selection when it was
connected to a material.

In order to obstruct the users vision as little as possible, the
selected areas of the curve are left as is, but a dark overlay
is drawn over unselected areas.

To make it work, the overlay requests the selection attribute and then
ensures that the evaluation is complete for curves. Then it retrieves
the evaluated selection GPU texture and passes that to the shader.
This reuses the existing generic attribute extraction system because
there currently wouldn't be any benefits to dealing with selection
separately, and because it avoids duplication of the logic that
extracts attributes from curves and evaluates them if necessary.

Differential Revision: https://developer.blender.org/D15219

1 files changed, 96 insertions, 0 deletions

diff --git a/source/blender/draw/engines/overlay/overlay_sculpt_curves.cc b/source/blender/draw/engines/overlay/overlay_sculpt_curves.cc
new file mode 100644
index 00000000000..b8021124f27
--- /dev/null
+++ b/source/blender/draw/engines/overlay/overlay_sculpt_curves.cc
@@ -0,0 +1,96 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright 2022 Blender Foundation. */
+
+/** \file
+ * \ingroup draw_engine
+ */
+
+#include "DRW_render.h"
+
+#include "draw_cache_impl.h"
+#include "overlay_private.h"
+
+#include "BKE_curves.hh"
+
+void OVERLAY_sculpt_curves_cache_init(OVERLAY_Data *vedata)
+{
+  OVERLAY_PassList *psl = vedata->psl;
+  OVERLAY_PrivateData *pd = vedata->stl->pd;
+
+  const DRWState state = DRW_STATE_WRITE_COLOR | DRW_STATE_DEPTH_EQUAL | DRW_STATE_BLEND_ALPHA;
+  DRW_PASS_CREATE(psl->sculpt_curves_selection_ps, state | pd->clipping_state);
+
+  GPUShader *sh = OVERLAY_shader_sculpt_curves_selection();
+  pd->sculpt_curves_selection_grp = DRW_shgroup_create(sh, psl->sculpt_curves_selection_ps);
+  DRWShadingGroup *grp = pd->sculpt_curves_selection_grp;
+
+  /* Reuse the same mask opacity from sculpt mode, since it wasn't worth it to add a different
+   * property yet. */
+  DRW_shgroup_uniform_float_copy(grp, "selection_opacity", pd->overlay.sculpt_mode_mask_opacity);
+}
+
+static bool everything_selected(const Curves &curves_id)
+{
+  if (!(curves_id.flag & CV_SCULPT_SELECTION_ENABLED)) {
+    /* When the selection is disabled, conceptually everything is selected. */
+    return true;
+  }
+  const blender::bke::CurvesGeometry &curves = blender::bke::CurvesGeometry::wrap(
+      curves_id.geometry);
+  blender::VArray<float> selection;
+  switch (curves_id.selection_domain) {
+    case ATTR_DOMAIN_POINT:
+      selection = curves.selection_point_float();
+      break;
+    case ATTR_DOMAIN_CURVE:
+      selection = curves.selection_curve_float();
+      break;
+  }
+  return selection.is_single() && selection.get_internal_single() == 1.0f;
+}
+
+void OVERLAY_sculpt_curves_cache_populate(OVERLAY_Data *vedata, Object *object)
+{
+  OVERLAY_PrivateData *pd = vedata->stl->pd;
+  Curves *curves = static_cast<Curves *>(object->data);
+
+  /* As an optimization, return early if everything is selected. */
+  if (everything_selected(*curves)) {
+    return;
+  }
+
+  /* Retrieve the location of the texture. */
+  const char *name = curves->selection_domain == ATTR_DOMAIN_POINT ? ".selection_point_float" :
+                                                                     ".selection_curve_float";
+
+  bool is_point_domain;
+  GPUTexture **texture = DRW_curves_texture_for_evaluated_attribute(
+      curves, name, &is_point_domain);
+  if (texture == nullptr) {
+    return;
+  }
+
+  /* Evaluate curves and their attributes if necessary. */
+  DRWShadingGroup *grp = DRW_shgroup_curves_create_sub(
+      object, pd->sculpt_curves_selection_grp, nullptr);
+  if (*texture == nullptr) {
+    return;
+  }
+
+  DRW_shgroup_uniform_bool_copy(grp, "is_point_domain", is_point_domain);
+  DRW_shgroup_uniform_texture(grp, "selection_tx", *texture);
+}
+
+void OVERLAY_sculpt_curves_draw(OVERLAY_Data *vedata)
+{
+  OVERLAY_PassList *psl = vedata->psl;
+  OVERLAY_PrivateData *pd = vedata->stl->pd;
+  OVERLAY_FramebufferList *fbl = vedata->fbl;
+
+  if (DRW_state_is_fbo()) {
+    GPU_framebuffer_bind(pd->painting.in_front ? fbl->overlay_in_front_fb :
+                                                 fbl->overlay_default_fb);
+  }
+
+  DRW_draw_pass(psl->sculpt_curves_selection_ps);
+}