source/blender/render/hydra/preview_engine.cc

@@ -1,6 +1,11 @@
 /* SPDX-License-Identifier: Apache-2.0
  * Copyright 2011-2022 Blender Foundation */
 
+#include <epoxy/gl.h>
+
+#include "GPU_framebuffer.h"
+#include "GPU_texture.h"
+
 #include "IMB_imbuf_types.h"
 
 #include "preview_engine.h"
@@ -34,6 +39,75 @@ void PreviewEngine::render(Depsgraph *depsgraph)
   update_render_result(pixels);
 }
 
+void PreviewEngineGPU::render(Depsgraph *depsgraph)
+{
+  prepare_for_render(depsgraph);
+
+  GPUFrameBuffer *framebuffer = GPU_framebuffer_create("fb_render_mat_prev_hydra");
+  GPUTexture *tex_color = GPU_texture_create_2d("tex_render_mat_prev_hydra_color",
+                                                resolution_[0],
+                                                resolution_[1],
+                                                1,
+                                                GPU_RGBA32F,
+                                                GPU_TEXTURE_USAGE_GENERAL,
+                                                nullptr);
+  GPUTexture *tex_depth = GPU_texture_create_2d("tex_render_mat_prev_hydra_depth",
+                                                resolution_[0],
+                                                resolution_[1],
+                                                1,
+                                                GPU_DEPTH32F_STENCIL8,
+                                                GPU_TEXTURE_USAGE_GENERAL,
+                                                nullptr);
+  GPU_texture_filter_mode(tex_color, true);
+  GPU_texture_mipmap_mode(tex_color, true, true);
+  GPU_texture_filter_mode(tex_depth, true);
+  GPU_texture_mipmap_mode(tex_depth, true, true);
+
+  GPU_framebuffer_ensure_config(
+      &framebuffer, {GPU_ATTACHMENT_TEXTURE(tex_depth), GPU_ATTACHMENT_TEXTURE(tex_color)});
+
+  GPU_framebuffer_bind(framebuffer);
+
+  float clear_color[4] = {0.0f, 0.0f, 0.0f, 1.0f};
+
+  GPU_framebuffer_clear_color_depth(framebuffer, clear_color, 1.0f);
+
+  /* Important: we have to create and bind at least one Vertex Array Object (VAO) before render
+     execution: More info at https://open.gl/drawing */
+  GLuint VAO;
+  glGenVertexArrays(1, &VAO);
+  glBindVertexArray(VAO);
+
+  engine_->Execute(render_index_.get(), &tasks_);
+
+  std::vector<float> &pixels = render_images_["Combined"];
+
+  while (true) {
+    if (RE_engine_test_break(bl_engine_)) {
+      break;
+    }
+
+    if (render_task_delegate_->is_converged()) {
+      break;
+    }
+
+    void *data = GPU_texture_read(tex_color, GPU_DATA_FLOAT, 0);
+    memcpy(pixels.data(), data, pixels.size() * sizeof(float));
+    MEM_freeN(data);
+    update_render_result();
+  }
+
+  void *data = GPU_texture_read(tex_color, GPU_DATA_FLOAT, 0);
+  memcpy(pixels.data(), data, pixels.size() * sizeof(float));
+  MEM_freeN(data);
+  update_render_result();
+
+  glDeleteVertexArrays(1, &VAO);
+  GPU_framebuffer_free(framebuffer);
+  GPU_texture_free(tex_color);
+  GPU_texture_free(tex_depth);
+}
+
 void PreviewEngine::update_render_result(std::vector<float> &pixels)
 {
   RenderResult *result = RE_engine_begin_result(

source/blender/render/hydra/preview_engine.h

@@ -17,4 +17,11 @@ class PreviewEngine : public FinalEngine {
   void update_render_result(std::vector<float> &pixels);
 };
 
+class PreviewEngineGPU : public FinalEngineGPU {
+ public:
+  using FinalEngineGPU::FinalEngineGPU;
+
+  void render(Depsgraph *depsgraph) override;
+};
+
 }  // namespace blender::render::hydra

source/blender/render/hydra/python.cc

@@ -71,7 +71,12 @@ static PyObject *engine_create_func(PyObject * /*self*/, PyObject *args)
       engine = new ViewportEngine(bl_engine, render_delegate_id);
     }
     else if (STREQ(engine_type, "PREVIEW")) {
-      engine = new PreviewEngine(bl_engine, render_delegate_id);
+      if (bl_engine->type->flag & RE_USE_GPU_CONTEXT) {
+        engine = new PreviewEngineGPU(bl_engine, render_delegate_id);
+      }
+      else {
+        engine = new PreviewEngine(bl_engine, render_delegate_id);
+      }
     }
     else {
       if (bl_engine->type->flag & RE_USE_GPU_CONTEXT) {