[Render/RenderSystem] The copied frame is the last executed pass'

- The render pass having been executed last is stored in the render graph and used afterward

- This is something that will be extremely useful later, e.g. for gamma correction, although it may be a bit too naïve at the moment
  - The last executed pass may not be the one the user wants to be displayed: there may be several final passes, one debug detached pass that's executed after the main ones, etc

examples/xrDemo.cpp

@@ -37,6 +37,7 @@ int main() {
     const auto colorBuffer = Raz::Texture2D::create(2468, 2584, Raz::TextureColorspace::RGBA);
     const auto depthBuffer = Raz::Texture2D::create(2468, 2584, Raz::TextureColorspace::DEPTH);
 
+    // The last executed pass *MUST* have a write color buffer, and at least the geometry pass *MUST* have a write depth buffer
     Raz::RenderPass& geomPass = render.getGeometryPass();
     geomPass.addWriteColorTexture(colorBuffer, 0);
     geomPass.setWriteDepthTexture(depthBuffer);

include/RaZ/Render/RenderGraph.hpp

@@ -52,6 +52,7 @@ class RenderGraph : public Graph<RenderPass> {
   RenderPass m_geometryPass {};
   std::vector<std::unique_ptr<RenderProcess>> m_renderProcesses {};
   std::unordered_set<const RenderPass*> m_executedPasses {};
+  const RenderPass* m_lastExecutedPass {};
 };
 
 } // namespace Raz

src/RaZ/Render/RenderGraph.cpp

@@ -44,6 +44,7 @@ void RenderGraph::execute(RenderSystem& renderSystem) {
   }
 
   executeGeometryPass(renderSystem);
+  m_lastExecutedPass = &m_geometryPass;
 
   m_executedPasses.reserve(m_nodes.size() + 1);
   m_executedPasses.emplace(&m_geometryPass);
@@ -110,6 +111,7 @@ void RenderGraph::executePass(const RenderPass& renderPass) {
     executePass(*parentPass);
 
   renderPass.execute();
+  m_lastExecutedPass = &renderPass;
 
   m_executedPasses.emplace(&renderPass);
 }

src/RaZ/Render/RenderSystem.cpp

@@ -336,18 +336,25 @@ void RenderSystem::renderXrFrame() {
 
     m_renderGraph.execute(*this);
 
-    // TODO: the returned color buffer must be the one from the render pass executed last
-    const Framebuffer& geomFramebuffer = m_renderGraph.m_geometryPass.getFramebuffer();
-    return std::make_pair(std::cref(geomFramebuffer.getColorBuffer(0)), std::cref(geomFramebuffer.getDepthBuffer()));
+    assert("Error: There is no valid last executed pass." && m_renderGraph.m_lastExecutedPass);
+    const Framebuffer& finalFramebuffer = m_renderGraph.m_lastExecutedPass->getFramebuffer();
+    assert("Error: The last executed pass must have at least one write color buffer." && finalFramebuffer.getColorBufferCount() >= 1);
+    assert("Error: Either the last executed pass or the geometry pass must have a write depth buffer."
+      && (finalFramebuffer.hasDepthBuffer() || m_renderGraph.m_geometryPass.getFramebuffer().hasDepthBuffer()));
+
+    const Texture2D& depthBuffer = (finalFramebuffer.hasDepthBuffer() ? finalFramebuffer.getDepthBuffer()
+                                                                      : m_renderGraph.m_geometryPass.getFramebuffer().getDepthBuffer());
+    return std::make_pair(std::cref(finalFramebuffer.getColorBuffer(0)), std::cref(depthBuffer));
   });
 
 #if !defined(RAZ_NO_WINDOW)
   if (!hasRendered)
     return;
 
-  // TODO: the copied color buffer must be the one from the render pass executed last
-  const Framebuffer& geomFramebuffer = m_renderGraph.m_geometryPass.getFramebuffer();
-  copyToWindow(geomFramebuffer.getColorBuffer(0), geomFramebuffer.getDepthBuffer(), m_window->getWidth(), m_window->getHeight());
+  const Framebuffer& finalFramebuffer = m_renderGraph.m_lastExecutedPass->getFramebuffer();
+  const Texture2D& depthBuffer        = (finalFramebuffer.hasDepthBuffer() ? finalFramebuffer.getDepthBuffer()
+                                                                           : m_renderGraph.m_geometryPass.getFramebuffer().getDepthBuffer());
+  copyToWindow(finalFramebuffer.getColorBuffer(0), depthBuffer, m_window->getWidth(), m_window->getHeight());
 #endif
 }
 #endif