[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, 36 insertions, 15 deletions

diff --git a/src/mbgl/style/layers/raster_layer_properties.hpp b/src/mbgl/style/layers/raster_layer_properties.hpp
index ddfb833e12..caa6d0c58d 100644
--- a/src/mbgl/style/layers/raster_layer_properties.hpp
+++ b/src/mbgl/style/layers/raster_layer_properties.hpp
@@ -9,22 +9,43 @@
 namespace mbgl {
 namespace style {
 
-class CascadeParameters;
-class CalculationParameters;
-
-class RasterPaintProperties {
-public:
-    void cascade(const CascadeParameters&);
-    bool recalculate(const CalculationParameters&);
-
-    PaintProperty<float> rasterOpacity { 1 };
-    PaintProperty<float> rasterHueRotate { 0 };
-    PaintProperty<float> rasterBrightnessMin { 0 };
-    PaintProperty<float> rasterBrightnessMax { 1 };
-    PaintProperty<float> rasterSaturation { 0 };
-    PaintProperty<float> rasterContrast { 0 };
-    PaintProperty<float> rasterFadeDuration { 300 };
+struct RasterOpacity : PaintProperty<float> {
+    static float defaultValue() { return 1; }
 };
 
+struct RasterHueRotate : PaintProperty<float> {
+    static float defaultValue() { return 0; }
+};
+
+struct RasterBrightnessMin : PaintProperty<float> {
+    static float defaultValue() { return 0; }
+};
+
+struct RasterBrightnessMax : PaintProperty<float> {
+    static float defaultValue() { return 1; }
+};
+
+struct RasterSaturation : PaintProperty<float> {
+    static float defaultValue() { return 0; }
+};
+
+struct RasterContrast : PaintProperty<float> {
+    static float defaultValue() { return 0; }
+};
+
+struct RasterFadeDuration : PaintProperty<float> {
+    static float defaultValue() { return 300; }
+};
+
+class RasterPaintProperties : public PaintProperties<
+    RasterOpacity,
+    RasterHueRotate,
+    RasterBrightnessMin,
+    RasterBrightnessMax,
+    RasterSaturation,
+    RasterContrast,
+    RasterFadeDuration
+> {};
+
 } // namespace style
 } // namespace mbgl