Fix 3D stencil mode incrementing for each drawable (#1345)

src/mbgl/gl/drawable_gl.cpp

@@ -46,7 +46,10 @@ void DrawableGL::draw(PaintParameters& parameters) const {
     // force disable depth test for debugging
     // context.setDepthMode({gfx::DepthFunctionType::Always, gfx::DepthMaskType::ReadOnly, {0,1}});
 
-    context.setStencilMode(makeStencilMode(parameters));
+    // For 3D mode, stenciling is handled by the layer group
+    if (!is3D) {
+        context.setStencilMode(makeStencilMode(parameters));
+    }
 
     context.setColorMode(getColorMode());
     context.setCullFaceMode(getCullFaceMode());
@@ -211,9 +214,7 @@ gfx::ColorMode DrawableGL::makeColorMode(PaintParameters& parameters) const {
 
 gfx::StencilMode DrawableGL::makeStencilMode(PaintParameters& parameters) const {
     if (enableStencil) {
-        if (is3D) {
-            return parameters.stencilModeFor3D();
-        } else if (tileID) {
+        if (!is3D && tileID) {
             return parameters.stencilModeForClipping(tileID->toUnwrapped());
         }
         assert(false);

src/mbgl/gl/layer_group_gl.cpp

@@ -46,6 +46,14 @@ void TileLayerGroupGL::render(RenderOrchestrator&, PaintParameters& parameters)
         return;
     }
 
+    auto& context = static_cast<gl::Context&>(parameters.context);
+
+    // `stencilModeFor3D` uses a different stencil mask value each time its called, so if the
+    // drawables in this layer use 3D stencil mode, we need to set it up here so that all the
+    // drawables end up using the same mode value.
+    bool stencil3d = false;
+    gfx::StencilMode stencilMode3d;
+
     if (getDrawableCount()) {
 #if !defined(NDEBUG)
         const auto label_clip = getName() + (getName().empty() ? "" : "-") + "tile-clip-masks";
@@ -55,12 +63,23 @@ void TileLayerGroupGL::render(RenderOrchestrator&, PaintParameters& parameters)
         // Collect the tile IDs relevant to stenciling and update the stencil buffer, if necessary.
         std::set<UnwrappedTileID> tileIDs;
         observeDrawables([&](const gfx::Drawable& drawable) {
-            if (drawable.getEnabled() && !drawable.getIs3D() && drawable.getEnableStencil() && drawable.getTileID() &&
-                drawable.hasRenderPass(parameters.pass)) {
-                tileIDs.emplace(drawable.getTileID()->toUnwrapped());
+            if (drawable.getEnabled() && drawable.getEnableStencil() && drawable.hasRenderPass(parameters.pass)) {
+                if (drawable.getIs3D()) {
+                    stencil3d = true;
+                }
+                if (!stencil3d && drawable.getTileID()) {
+                    tileIDs.emplace(drawable.getTileID()->toUnwrapped());
+                }
             }
         });
-        parameters.renderTileClippingMasks(tileIDs);
+
+        // If we're doing 3D stenciling, set up the single-value stencil mask.
+        // If we're doing 2D stenciling, render each tile with a different value.
+        if (stencil3d) {
+            stencilMode3d = parameters.stencilModeFor3D();
+        } else {
+            parameters.renderTileClippingMasks(tileIDs);
+        }
     }
 
 #if !defined(NDEBUG)
@@ -86,6 +105,10 @@ void TileLayerGroupGL::render(RenderOrchestrator&, PaintParameters& parameters)
             tweaker->execute(drawable, parameters);
         }
 
+        if (stencil3d) {
+            context.setStencilMode(drawable.getEnableStencil() ? stencilMode3d : gfx::StencilMode::disabled());
+        }
+
         drawable.draw(parameters);
     });
 }