[core] Convert style properties to a tuple-based approach

This converts the style property classes (CirclePaintProperties and so on) to the same tuple-based approach as gl::Attribute and gl::Uniform. The approach is outlined in https://github.com/mapbox/cpp/blob/master/C%2B%2B%20Structural%20Metaprogramming.md.

The main advantage of this approach is it allows writing algorithms that work on sets of style properties, without resorting to code generation or manually repetitive code. This lets us iterate on approaches to data-driven properties more easily.

Another advantage is that the cascading, unevaluated, and evaluated states of a set of properties exist as independent structures, instead of individual properties holding their own state. This is a more functional approach that makes data flow clearer and reduces state.

1 files changed, 15 insertions, 15 deletions

diff --git a/src/mbgl/text/quads.cpp b/src/mbgl/text/quads.cpp
index 3f142cd908..1a05e6f94f 100644
--- a/src/mbgl/text/quads.cpp
+++ b/src/mbgl/text/quads.cpp
@@ -14,7 +14,7 @@ using namespace style;
 const float globalMinScale = 0.5f; // underscale by 1 zoom level
 
 SymbolQuads getIconQuads(Anchor& anchor, const PositionedIcon& shapedIcon,
-        const GeometryCoordinates& line, const SymbolLayoutProperties& layout,
+        const GeometryCoordinates& line, const SymbolLayoutProperties::Evaluated& layout,
         const style::SymbolPlacementType placement, const Shaping& shapedText) {
 
     auto image = *(shapedIcon.image);
@@ -29,24 +29,24 @@ SymbolQuads getIconQuads(Anchor& anchor, const PositionedIcon& shapedIcon,
     Point<float> br;
     Point<float> bl;
 
-    if (layout.iconTextFit != IconTextFitType::None && shapedText) {
+    if (layout.get<IconTextFit>() != IconTextFitType::None && shapedText) {
         auto iconWidth = right - left;
         auto iconHeight = bottom - top;
-        auto size = layout.textSize / 24.0f;
+        auto size = layout.get<TextSize>() / 24.0f;
         auto textLeft = shapedText.left * size;
         auto textRight = shapedText.right * size;
         auto textTop = shapedText.top * size;
         auto textBottom = shapedText.bottom * size;
         auto textWidth = textRight - textLeft;
         auto textHeight = textBottom - textTop;;
-        auto padT = layout.iconTextFitPadding.value[0];
-        auto padR = layout.iconTextFitPadding.value[1];
-        auto padB = layout.iconTextFitPadding.value[2];
-        auto padL = layout.iconTextFitPadding.value[3];
-        auto offsetY = layout.iconTextFit == IconTextFitType::Width ? (textHeight - iconHeight) * 0.5 : 0;
-        auto offsetX = layout.iconTextFit == IconTextFitType::Height ? (textWidth - iconWidth) * 0.5 : 0;
-        auto width = layout.iconTextFit == IconTextFitType::Width || layout.iconTextFit == IconTextFitType::Both ? textWidth : iconWidth;
-        auto height = layout.iconTextFit == IconTextFitType::Height || layout.iconTextFit == IconTextFitType::Both ? textHeight : iconHeight;
+        auto padT = layout.get<IconTextFitPadding>()[0];
+        auto padR = layout.get<IconTextFitPadding>()[1];
+        auto padB = layout.get<IconTextFitPadding>()[2];
+        auto padL = layout.get<IconTextFitPadding>()[3];
+        auto offsetY = layout.get<IconTextFit>() == IconTextFitType::Width ? (textHeight - iconHeight) * 0.5 : 0;
+        auto offsetX = layout.get<IconTextFit>() == IconTextFitType::Height ? (textWidth - iconWidth) * 0.5 : 0;
+        auto width = layout.get<IconTextFit>() == IconTextFitType::Width || layout.get<IconTextFit>() == IconTextFitType::Both ? textWidth : iconWidth;
+        auto height = layout.get<IconTextFit>() == IconTextFitType::Height || layout.get<IconTextFit>() == IconTextFitType::Both ? textHeight : iconHeight;
         left = textLeft + offsetX - padL;
         top = textTop + offsetY - padT;
         right = textLeft + offsetX + padR + width;
@@ -62,7 +62,7 @@ SymbolQuads getIconQuads(Anchor& anchor, const PositionedIcon& shapedIcon,
         bl = {left, bottom};
     }
 
-    float angle = layout.iconRotate * util::DEG2RAD;
+    float angle = layout.get<IconRotate>() * util::DEG2RAD;
     if (placement == style::SymbolPlacementType::Line) {
         assert(static_cast<unsigned int>(anchor.segment) < line.size());
         const GeometryCoordinate &prev= line[anchor.segment];
@@ -165,11 +165,11 @@ void getSegmentGlyphs(std::back_insert_iterator<GlyphInstances> glyphs, Anchor &
 }
 
 SymbolQuads getGlyphQuads(Anchor& anchor, const Shaping& shapedText,
-        const float boxScale, const GeometryCoordinates& line, const SymbolLayoutProperties& layout,
+        const float boxScale, const GeometryCoordinates& line, const SymbolLayoutProperties::Evaluated& layout,
         const style::SymbolPlacementType placement, const GlyphPositions& face) {
 
-    const float textRotate = layout.textRotate * util::DEG2RAD;
-    const bool keepUpright = layout.textKeepUpright;
+    const float textRotate = layout.get<TextRotate>() * util::DEG2RAD;
+    const bool keepUpright = layout.get<TextKeepUpright>();
 
     SymbolQuads quads;