Render translucent background layers (fixes #1514)

2 files changed, 50 insertions, 72 deletions

diff --git a/src/mbgl/renderer/painter.cpp b/src/mbgl/renderer/painter.cpp
index f306dec2d3..653bae0d68 100644
--- a/src/mbgl/renderer/painter.cpp
+++ b/src/mbgl/renderer/painter.cpp
@@ -159,20 +159,6 @@ void Painter::clear() {
     MBGL_CHECK_ERROR(glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT | GL_DEPTH_BUFFER_BIT));
 }
 
-void Painter::setOpaque() {
-    if (pass != RenderPass::Opaque) {
-        pass = RenderPass::Opaque;
-        config.blend = false;
-    }
-}
-
-void Painter::setTranslucent() {
-    if (pass != RenderPass::Translucent) {
-        pass = RenderPass::Translucent;
-        config.blend = true;
-    }
-}
-
 void Painter::setStrata(float value) {
     strata = value;
 }
@@ -241,66 +227,19 @@ void Painter::render(const Style& style, TransformState state_, TimePoint time)
     if (debug::renderTree) { Log::Info(Event::Render, "{"); indent++; }
 
     // TODO: Correctly compute the number of layers recursively beforehand.
-    const float strata_thickness = 1.0f / (order.size() + 1);
-
-    // Layer index
-    int i = 0;
+    const float strataThickness = 1.0f / (order.size() + 1);
 
     // - OPAQUE PASS -------------------------------------------------------------------------------
     // Render everything top-to-bottom by using reverse iterators. Render opaque objects first.
-    {
-        const gl::debugging::group _("opaque");
-
-        if (debug::renderTree) {
-            Log::Info(Event::Render, "%*s%s", indent++ * 4, "", "OPAQUE {");
-        }
-        i = 0;
-        setOpaque();
-        for (auto it = order.rbegin(), end = order.rend(); it != end; ++it, ++i) {
-            const auto& item = *it;
-            if (item.bucket && item.tile) {
-                if (item.hasRenderPass(RenderPass::Opaque)) {
-                    const gl::debugging::group group(item.layer.id + " - " + std::string(item.tile->id));
-                    setStrata(i * strata_thickness);
-                    prepareTile(*item.tile);
-                    item.bucket->render(*this, item.layer, item.tile->id, item.tile->matrix);
-                }
-            } else {
-                const gl::debugging::group group("background");
-                setStrata(i * strata_thickness);
-                renderBackground(item.layer);
-            }
-        }
-        if (debug::renderTree) {
-            Log::Info(Event::Render, "%*s%s", --indent * 4, "", "}");
-        }
-    }
+    renderPass(RenderPass::Opaque,
+               order.rbegin(), order.rend(),
+               0, 1, strataThickness);
 
     // - TRANSLUCENT PASS --------------------------------------------------------------------------
     // Make a second pass, rendering translucent objects. This time, we render bottom-to-top.
-    {
-        const gl::debugging::group _("translucent");
-
-        if (debug::renderTree) {
-            Log::Info(Event::Render, "%*s%s", indent++ * 4, "", "TRANSLUCENT {");
-        }
-        --i; // After the last iteration, this is incremented, so we have to decrement it again.
-        setTranslucent();
-        for (auto it = order.begin(), end = order.end(); it != end; ++it, --i) {
-            const auto& item = *it;
-            if (item.bucket && item.tile) {
-                if (item.hasRenderPass(RenderPass::Translucent)) {
-                    const gl::debugging::group group(item.layer.id + " - " + std::string(item.tile->id));
-                    setStrata(i * strata_thickness);
-                    prepareTile(*item.tile);
-                    item.bucket->render(*this, item.layer, item.tile->id, item.tile->matrix);
-                }
-            }
-        }
-        if (debug::renderTree) {
-            Log::Info(Event::Render, "%*s%s", --indent * 4, "", "}");
-        }
-    }
+    renderPass(RenderPass::Translucent,
+               order.begin(), order.end(),
+               order.size() - 1, -1, strataThickness);
 
     if (debug::renderTree) { Log::Info(Event::Render, "}"); indent--; }
 
@@ -328,6 +267,43 @@ void Painter::render(const Style& style, TransformState state_, TimePoint time)
     }
 }
 
+template <class Iterator>
+void Painter::renderPass(RenderPass pass_,
+                         Iterator it, Iterator end,
+                         std::size_t i, int8_t increment,
+                         const float strataThickness) {
+    pass = pass_;
+
+    const char * passName = pass == RenderPass::Opaque ? "opaque" : "translucent";
+    const gl::debugging::group _(passName);
+
+    if (debug::renderTree) {
+        Log::Info(Event::Render, "%*s%s {", indent++ * 4, "", passName);
+    }
+
+    config.blend = pass == RenderPass::Translucent;
+
+    for (; it != end; ++it, i += increment) {
+        const auto& item = *it;
+        if (item.bucket && item.tile) {
+            if (item.hasRenderPass(pass)) {
+                const gl::debugging::group group(item.layer.id + " - " + std::string(item.tile->id));
+                setStrata(i * strataThickness);
+                prepareTile(*item.tile);
+                item.bucket->render(*this, item.layer, item.tile->id, item.tile->matrix);
+            }
+        } else {
+            const gl::debugging::group group("background");
+            setStrata(i * strataThickness);
+            renderBackground(item.layer);
+        }
+    }
+
+    if (debug::renderTree) {
+        Log::Info(Event::Render, "%*s%s", --indent * 4, "", "}");
+    }
+}
+
 std::vector<RenderItem> Painter::determineRenderOrder(const Style& style) {
     std::vector<RenderItem> order;
 
diff --git a/src/mbgl/renderer/painter.hpp b/src/mbgl/renderer/painter.hpp
index 54c23b393a..871612ef43 100644
--- a/src/mbgl/renderer/painter.hpp
+++ b/src/mbgl/renderer/painter.hpp
@@ -123,10 +123,6 @@ public:
     // Changes whether debug information is drawn onto the map
     void setDebug(bool enabled);
 
-    // Opaque/Translucent pass setting
-    void setOpaque();
-    void setTranslucent();
-
     // Configures the painter strata that is used for early z-culling of fragments.
     void setStrata(float strata);
 
@@ -148,6 +144,12 @@ private:
     std::vector<RenderItem> determineRenderOrder(const Style& style);
     static RenderPass determineRenderPasses(const StyleLayer&);
 
+    template <class Iterator>
+    void renderPass(RenderPass,
+                    Iterator it, Iterator end,
+                    std::size_t i, int8_t iIncrement,
+                    const float strataThickness);
+
     void prepareTile(const Tile& tile);
 
     template <typename BucketProperties, typename StyleProperties>