Python API: option for render engines to delegate Freestyle render to Eevee

Eevee is now used for Freestyle rendering by default, since other engines are
unlikely to have support for this. Workbench and Cycles do their own rendering.

RenderEngine add-ons can do their own Freestyle rendering by setting
bl_use_custom_freestyle = True.

Differential Revision: https://developer.blender.org/D8335

2 files changed, 26 insertions, 0 deletions

diff --git a/source/blender/render/RE_engine.h b/source/blender/render/RE_engine.h
index 1af40ac760b..c31a41f66d5 100644
--- a/source/blender/render/RE_engine.h
+++ b/source/blender/render/RE_engine.h
@@ -64,6 +64,7 @@ extern "C" {
 #define RE_USE_SPHERICAL_STEREO 128
 #define RE_USE_STEREO_VIEWPORT 256
 #define RE_USE_GPU_CONTEXT 512
+#define RE_USE_CUSTOM_FREESTYLE 1024
 
 /* RenderEngine.flag */
 #define RE_ENGINE_ANIMATION 1
diff --git a/source/blender/render/intern/pipeline.c b/source/blender/render/intern/pipeline.c
index 320f8b8ed03..8567835f55c 100644
--- a/source/blender/render/intern/pipeline.c
+++ b/source/blender/render/intern/pipeline.c
@@ -2007,13 +2007,38 @@ void RE_RenderFrame(Render *re,
   G.is_rendering = false;
 }
 
+static void change_renderdata_engine(Render *re, const char *new_engine)
+{
+  if (!STREQ(re->r.engine, new_engine)) {
+    if (re->engine) {
+      RE_engine_free(re->engine);
+      re->engine = NULL;
+    }
+    BLI_strncpy(re->r.engine, new_engine, sizeof(re->r.engine));
+  }
+}
+
 #ifdef WITH_FREESTYLE
+static bool use_eevee_for_freestyle_render(Render *re)
+{
+  RenderEngineType *type = RE_engines_find(re->r.engine);
+  return !(type->flag & RE_USE_CUSTOM_FREESTYLE);
+}
+
 void RE_RenderFreestyleStrokes(Render *re, Main *bmain, Scene *scene, int render)
 {
   re->result_ok = 0;
   if (render_init_from_main(re, &scene->r, bmain, scene, NULL, NULL, 0, 0)) {
     if (render) {
+      char scene_engine[32];
+      BLI_strncpy(scene_engine, re->r.engine, sizeof(scene_engine));
+      if (use_eevee_for_freestyle_render(re)) {
+        change_renderdata_engine(re, RE_engine_id_BLENDER_EEVEE);
+      }
+
       do_render_3d(re);
+
+      change_renderdata_engine(re, scene_engine);
     }
   }
   re->result_ok = 1;