Replace size() with empty() whenever possible

Before C++11, std::list's implementation of size was O(n). It should be
all O(1) now, but it is probably still a good idea to use empty() to
emphasize the intend.

7 files changed, 19 insertions, 21 deletions

diff --git a/src/mbgl/renderer/fill_bucket.cpp b/src/mbgl/renderer/fill_bucket.cpp
index 0efe1b4373..fd4df4314a 100644
--- a/src/mbgl/renderer/fill_bucket.cpp
+++ b/src/mbgl/renderer/fill_bucket.cpp
@@ -67,7 +67,7 @@ void FillBucket::addGeometry(const GeometryCollection& geometryCollection) {
         for (auto& v : line_) {
             line.emplace_back(v.x, v.y);
         }
-        if (line.size()) {
+        if (!line.empty()) {
             clipper.AddPath(line, ClipperLib::ptSubject, true);
             line.clear();
             hasVertices = true;
@@ -87,7 +87,7 @@ void FillBucket::tessellate() {
     clipper.Execute(ClipperLib::ctUnion, polygons, ClipperLib::pftEvenOdd, ClipperLib::pftEvenOdd);
     clipper.Clear();
 
-    if (polygons.size() == 0) {
+    if (polygons.empty()) {
         return;
     }
 
@@ -100,7 +100,7 @@ void FillBucket::tessellate() {
         throw geometry_too_long_exception();
     }
 
-    if (!lineGroups.size() || (lineGroups.back()->vertex_length + total_vertex_count > 65535)) {
+    if (lineGroups.empty() || (lineGroups.back()->vertex_length + total_vertex_count > 65535)) {
         // Move to a new group because the old one can't hold the geometry.
         lineGroups.emplace_back(std::make_unique<LineGroup>());
     }
@@ -147,7 +147,7 @@ void FillBucket::tessellate() {
             }
         }
 
-        if (!triangleGroups.size() || (triangleGroups.back()->vertex_length + total_vertex_count > 65535)) {
+        if (triangleGroups.empty() || (triangleGroups.back()->vertex_length + total_vertex_count > 65535)) {
             // Move to a new group because the old one can't hold the geometry.
             triangleGroups.emplace_back(std::make_unique<TriangleGroup>());
         }
diff --git a/src/mbgl/renderer/frame_history.cpp b/src/mbgl/renderer/frame_history.cpp
index 73336c029f..c95e82631e 100644
--- a/src/mbgl/renderer/frame_history.cpp
+++ b/src/mbgl/renderer/frame_history.cpp
@@ -5,18 +5,18 @@ using namespace mbgl;
 // Record frame history that will be used to calculate fading params
 void FrameHistory::record(const TimePoint& now, float zoom) {
     // first frame ever
-    if (!history.size()) {
+    if (history.empty()) {
         history.emplace_back(FrameSnapshot{TimePoint::min(), zoom});
         history.emplace_back(FrameSnapshot{TimePoint::min(), zoom});
     }
 
-    if (history.size() > 0 || history.back().z != zoom) {
+    if (!history.empty() || history.back().z != zoom) {
         history.emplace_back(FrameSnapshot{now, zoom});
     }
 }
 
 bool FrameHistory::needsAnimation(const Duration& duration) const {
-    if (!history.size()) {
+    if (history.empty()) {
         return false;
     }
 
diff --git a/src/mbgl/renderer/line_bucket.cpp b/src/mbgl/renderer/line_bucket.cpp
index 446c75de76..24bda6d0a9 100644
--- a/src/mbgl/renderer/line_bucket.cpp
+++ b/src/mbgl/renderer/line_bucket.cpp
@@ -308,8 +308,7 @@ void LineBucket::addGeometry(const std::vector<Coordinate>& vertices) {
 
     // Store the triangle/line groups.
     {
-        if (!triangleGroups.size() ||
-            (triangleGroups.back()->vertex_length + vertexCount > 65535)) {
+        if (triangleGroups.empty() || (triangleGroups.back()->vertex_length + vertexCount > 65535)) {
             // Move to a new group because the old one can't hold the geometry.
             triangleGroups.emplace_back(std::make_unique<TriangleGroup>());
         }
diff --git a/src/mbgl/renderer/painter.cpp b/src/mbgl/renderer/painter.cpp
index db0393b003..16b44916a3 100644
--- a/src/mbgl/renderer/painter.cpp
+++ b/src/mbgl/renderer/painter.cpp
@@ -374,7 +374,7 @@ RenderPass Painter::determineRenderPasses(const StyleLayer& layer) {
         if (properties.antialias) {
             passes |= RenderPass::Translucent;
         }
-        if (properties.image.from.size() || alpha < 1.0f) {
+        if (!properties.image.from.empty() || alpha < 1.0f) {
             passes |= RenderPass::Translucent;
         } else {
             passes |= RenderPass::Opaque;
@@ -389,7 +389,7 @@ RenderPass Painter::determineRenderPasses(const StyleLayer& layer) {
 void Painter::renderBackground(const StyleLayer &layer_desc) {
     const BackgroundProperties& properties = layer_desc.getProperties<BackgroundProperties>();
 
-    if (properties.image.to.size()) {
+    if (!properties.image.to.empty()) {
         if ((properties.opacity >= 1.0f) != (pass == RenderPass::Opaque))
             return;
 
diff --git a/src/mbgl/renderer/painter_fill.cpp b/src/mbgl/renderer/painter_fill.cpp
index 2f683665ed..414ec2bbcb 100644
--- a/src/mbgl/renderer/painter_fill.cpp
+++ b/src/mbgl/renderer/painter_fill.cpp
@@ -33,7 +33,7 @@ void Painter::renderFill(FillBucket& bucket, const StyleLayer &layer_desc, const
         stroke_color[3] *= properties.opacity;
     }
 
-    const bool pattern = properties.image.from.size();
+    const bool pattern = !properties.image.from.empty();
 
     bool outline = properties.antialias && !pattern && stroke_color != fill_color;
     bool fringeline = properties.antialias && !pattern && stroke_color == fill_color;
diff --git a/src/mbgl/renderer/painter_line.cpp b/src/mbgl/renderer/painter_line.cpp
index 1ef9214102..0860bbc03a 100644
--- a/src/mbgl/renderer/painter_line.cpp
+++ b/src/mbgl/renderer/painter_line.cpp
@@ -55,7 +55,7 @@ void Painter::renderLine(LineBucket& bucket, const StyleLayer &layer_desc, const
 
     config.depthRange = { strata, 1.0f };
 
-    if (properties.dash_array.from.size()) {
+    if (!properties.dash_array.from.empty()) {
 
         useProgram(linesdfShader->program);
 
@@ -86,7 +86,7 @@ void Painter::renderLine(LineBucket& bucket, const StyleLayer &layer_desc, const
 
         bucket.drawLineSDF(*linesdfShader);
 
-    } else if (properties.image.from.size()) {
+    } else if (!properties.image.from.empty()) {
         SpriteAtlasPosition imagePosA = spriteAtlas->getPosition(properties.image.from, true);
         SpriteAtlasPosition imagePosB = spriteAtlas->getPosition(properties.image.to, true);
 
diff --git a/src/mbgl/renderer/symbol_bucket.cpp b/src/mbgl/renderer/symbol_bucket.cpp
index c99b725e7f..c4347febbc 100644
--- a/src/mbgl/renderer/symbol_bucket.cpp
+++ b/src/mbgl/renderer/symbol_bucket.cpp
@@ -81,7 +81,7 @@ void SymbolBucket::render(Painter& painter,
     painter.renderSymbol(*this, layer_desc, id, matrix);
 }
 
-bool SymbolBucket::hasData() const { return hasTextData() || hasIconData() || symbolInstances.size(); }
+bool SymbolBucket::hasData() const { return hasTextData() || hasIconData() || !symbolInstances.empty(); }
 
 bool SymbolBucket::hasTextData() const { return renderData && !renderData->text.groups.empty(); }
 
@@ -128,7 +128,7 @@ bool SymbolBucket::needsDependencies(const GeometryTileLayer& layer,
 
             ft.label = util::utf8_to_utf32::convert(u8string);
 
-            if (ft.label.size()) {
+            if (!ft.label.empty()) {
                 // Loop through all characters of this text and collect unique codepoints.
                 for (char32_t chr : ft.label) {
                     ranges.insert(getGlyphRange(chr));
@@ -219,7 +219,7 @@ void SymbolBucket::addFeatures(uintptr_t tileUID,
     auto fontStack = glyphStore.getFontStack(layout.text.font);
 
     for (const auto& feature : features) {
-        if (!feature.geometry.size()) continue;
+        if (feature.geometry.empty()) continue;
 
         Shaping shapedText;
         PositionedIcon shapedIcon;
@@ -298,7 +298,7 @@ void SymbolBucket::addFeature(const std::vector<std::vector<Coordinate>> &lines,
         lines;
 
     for (const auto& line : clippedLines) {
-        if (!line.size()) continue;
+        if (line.empty()) continue;
 
         // Calculate the anchor points around which you want to place labels
         Anchors anchors = isLine ?
@@ -478,8 +478,7 @@ void SymbolBucket::addSymbols(Buffer &buffer, const SymbolQuads &symbols, float
 
         const int glyph_vertex_length = 4;
 
-        if (!buffer.groups.size() ||
-            (buffer.groups.back()->vertex_length + glyph_vertex_length > 65535)) {
+        if (buffer.groups.empty() || (buffer.groups.back()->vertex_length + glyph_vertex_length > 65535)) {
             // Move to a new group because the old one can't hold the geometry.
             buffer.groups.emplace_back(std::make_unique<GroupType>());
         }
@@ -540,7 +539,7 @@ void SymbolBucket::addToDebugBuffers() {
                 const float placementZoom= util::max(0.0f, util::min(25.0f, static_cast<float>(zoom + log(box.placementScale) / log(2))));
 
                 auto& collisionBox = renderDataInProgress->collisionBox;
-                if (!collisionBox.groups.size()) {
+                if (collisionBox.groups.empty()) {
                     // Move to a new group because the old one can't hold the geometry.
                     collisionBox.groups.emplace_back(std::make_unique<CollisionBoxElementGroup>());
                 }