Preserve depth buffer between 3D layers + optimize render order (#9931)

Port of https://github.com/mapbox/mapbox-gl-js/pull/5101: adds a new render pass `Pass3D` before any other rendering wherein we render layers with 3D passes (fill-extrusion layers) to offscreen framebuffers, sharing a depth renderbuffer between those layers in order to render 3D space correctly. Those framebuffers are saved on the RenderLayers and copied back to the map during the translucent pass. Rendering to offscreen framebuffers before we do any clear + draw means we can avoid expensive framebuffer restores.

1 files changed, 38 insertions, 9 deletions

diff --git a/src/mbgl/renderer/renderer_impl.cpp b/src/mbgl/renderer/renderer_impl.cpp
index a5d23333ac..c45295b693 100644
--- a/src/mbgl/renderer/renderer_impl.cpp
+++ b/src/mbgl/renderer/renderer_impl.cpp
@@ -13,6 +13,7 @@
 #include <mbgl/renderer/render_tile.hpp>
 #include <mbgl/renderer/layers/render_background_layer.hpp>
 #include <mbgl/renderer/layers/render_custom_layer.hpp>
+#include <mbgl/renderer/layers/render_fill_extrusion_layer.hpp>
 #include <mbgl/renderer/style_diff.hpp>
 #include <mbgl/renderer/query.hpp>
 #include <mbgl/renderer/backend_scope.hpp>
@@ -276,6 +277,10 @@ void Renderer::Impl::render(const UpdateParameters& updateParameters) {
         RenderLayer* layer = getRenderLayer(layerImpl->id);
         assert(layer);
 
+        if (!parameters.staticData.has3D && layer->is<RenderFillExtrusionLayer>()) {
+            parameters.staticData.has3D = true;
+        }
+
         if (!layer->needsRendering(zoomHistory.lastZoom)) {
             continue;
         }
@@ -372,6 +377,39 @@ void Renderer::Impl::render(const UpdateParameters& updateParameters) {
         parameters.imageManager.upload(parameters.context, 0);
         parameters.lineAtlas.upload(parameters.context, 0);
         parameters.frameHistory.upload(parameters.context, 0);
+
+        // Update all clipping IDs + upload buckets.
+        for (const auto& entry : renderSources) {
+            if (entry.second->isEnabled()) {
+                entry.second->startRender(parameters);
+            }
+        }
+    }
+
+    // - 3D PASS -------------------------------------------------------------------------------------
+    // Renders any 3D layers bottom-to-top to unique FBOs with texture attachments, but share the same
+    // depth rbo between them.
+    if (parameters.staticData.has3D) {
+        parameters.staticData.backendSize = parameters.backend.getFramebufferSize();
+
+        MBGL_DEBUG_GROUP(parameters.context, "3d");
+        parameters.pass = RenderPass::Pass3D;
+
+        if (!parameters.staticData.depthRenderbuffer ||
+            parameters.staticData.depthRenderbuffer->size != parameters.staticData.backendSize) {
+            parameters.staticData.depthRenderbuffer =
+                parameters.context.createRenderbuffer<gl::RenderbufferType::DepthComponent>(parameters.staticData.backendSize);
+        }
+        parameters.staticData.depthRenderbuffer->shouldClear(true);
+
+        uint32_t i = static_cast<uint32_t>(order.size()) - 1;
+        for (auto it = order.begin(); it != order.end(); ++it, --i) {
+            parameters.currentLayer = i;
+            if (it->layer.hasRenderPass(parameters.pass)) {
+                MBGL_DEBUG_GROUP(parameters.context, it->layer.getID());
+                it->layer.render(parameters, it->source);
+            }
+        }
     }
 
     // - CLEAR -------------------------------------------------------------------------------------
@@ -390,15 +428,6 @@ void Renderer::Impl::render(const UpdateParameters& updateParameters) {
     // - CLIPPING MASKS ----------------------------------------------------------------------------
     // Draws the clipping masks to the stencil buffer.
     {
-        MBGL_DEBUG_GROUP(parameters.context, "clip");
-
-        // Update all clipping IDs.
-        for (const auto& entry : renderSources) {
-            if (entry.second->isEnabled()) {
-                entry.second->startRender(parameters);
-            }
-        }
-
         MBGL_DEBUG_GROUP(parameters.context, "clipping masks");
 
         static const style::FillPaintProperties::PossiblyEvaluated properties {};