[core] Add DDS support for {text,icon}-size (#8593)

* Update gl-js and generate style code

* Factor out packUint8Pair() helper function

* Draft implementation of DDS for {text,icon}-size

Ports https://github.com/mapbox/mapbox-gl-js/pull/4455

* Fix text-size/composite-function-line-placement test

* Refactor to PaintPropertyBinders-like strategy

* Dedupe gl::Program construction

* Use exponential function base for interpolation

* Dedupe coveringZoomStops method

* Fixup tests

* Fix CI errors (hidden within #if block)

5 files changed, 12 insertions, 20 deletions

diff --git a/src/mbgl/style/layers/symbol_layer.cpp b/src/mbgl/style/layers/symbol_layer.cpp
index bd5cf30ad6..e79a3f967f 100644
--- a/src/mbgl/style/layers/symbol_layer.cpp
+++ b/src/mbgl/style/layers/symbol_layer.cpp
@@ -161,15 +161,15 @@ void SymbolLayer::setIconRotationAlignment(PropertyValue<AlignmentType> value) {
     impl->layout.unevaluated.get<IconRotationAlignment>() = value;
     impl->observer->onLayerLayoutPropertyChanged(*this, "icon-rotation-alignment");
 }
-PropertyValue<float> SymbolLayer::getDefaultIconSize() {
+DataDrivenPropertyValue<float> SymbolLayer::getDefaultIconSize() {
     return IconSize::defaultValue();
 }
 
-PropertyValue<float> SymbolLayer::getIconSize() const {
+DataDrivenPropertyValue<float> SymbolLayer::getIconSize() const {
     return impl->layout.unevaluated.get<IconSize>();
 }
 
-void SymbolLayer::setIconSize(PropertyValue<float> value) {
+void SymbolLayer::setIconSize(DataDrivenPropertyValue<float> value) {
     if (value == getIconSize())
         return;
     impl->layout.unevaluated.get<IconSize>() = value;
@@ -329,15 +329,15 @@ void SymbolLayer::setTextFont(PropertyValue<std::vector<std::string>> value) {
     impl->layout.unevaluated.get<TextFont>() = value;
     impl->observer->onLayerLayoutPropertyChanged(*this, "text-font");
 }
-PropertyValue<float> SymbolLayer::getDefaultTextSize() {
+DataDrivenPropertyValue<float> SymbolLayer::getDefaultTextSize() {
     return TextSize::defaultValue();
 }
 
-PropertyValue<float> SymbolLayer::getTextSize() const {
+DataDrivenPropertyValue<float> SymbolLayer::getTextSize() const {
     return impl->layout.unevaluated.get<TextSize>();
 }
 
-void SymbolLayer::setTextSize(PropertyValue<float> value) {
+void SymbolLayer::setTextSize(DataDrivenPropertyValue<float> value) {
     if (value == getTextSize())
         return;
     impl->layout.unevaluated.get<TextSize>() = value;
diff --git a/src/mbgl/style/layers/symbol_layer_impl.cpp b/src/mbgl/style/layers/symbol_layer_impl.cpp
index c637770c04..109d1c43e7 100644
--- a/src/mbgl/style/layers/symbol_layer_impl.cpp
+++ b/src/mbgl/style/layers/symbol_layer_impl.cpp
@@ -13,10 +13,6 @@ void SymbolLayer::Impl::cascade(const CascadeParameters& parameters) {
 bool SymbolLayer::Impl::evaluate(const PropertyEvaluationParameters& parameters) {
     paint.evaluate(parameters);
 
-    // text-size and icon-size are layout properties but they also need to be evaluated as paint properties:
-    iconSize = layout.evaluate<IconSize>(parameters);
-    textSize = layout.evaluate<TextSize>(parameters);
-    
     auto hasIconOpacity = paint.evaluated.get<IconColor>().constantOr(Color::black()).a > 0 ||
         paint.evaluated.get<IconHaloColor>().constantOr(Color::black()).a > 0;
     auto hasTextOpacity = paint.evaluated.get<TextColor>().constantOr(Color::black()).a > 0 ||
diff --git a/src/mbgl/style/layers/symbol_layer_impl.hpp b/src/mbgl/style/layers/symbol_layer_impl.hpp
index db20989f01..3d81ff1f69 100644
--- a/src/mbgl/style/layers/symbol_layer_impl.hpp
+++ b/src/mbgl/style/layers/symbol_layer_impl.hpp
@@ -44,7 +44,7 @@ public:
     // Layout
     AlignmentType pitchAlignment;
     AlignmentType rotationAlignment;
-    float layoutSize;
+    PossiblyEvaluatedPropertyValue<float> layoutSize;
 
     // Paint
     std::array<float, 2> translate;
diff --git a/src/mbgl/style/layers/symbol_layer_properties.hpp b/src/mbgl/style/layers/symbol_layer_properties.hpp
index 4f63ed419a..42f593890b 100644
--- a/src/mbgl/style/layers/symbol_layer_properties.hpp
+++ b/src/mbgl/style/layers/symbol_layer_properties.hpp
@@ -45,7 +45,7 @@ struct IconRotationAlignment : LayoutProperty<AlignmentType> {
     static AlignmentType defaultValue() { return AlignmentType::Auto; }
 };
 
-struct IconSize : LayoutProperty<float> {
+struct IconSize : DataDrivenLayoutProperty<float> {
     static constexpr const char * key = "icon-size";
     static float defaultValue() { return 1; }
 };
@@ -105,7 +105,7 @@ struct TextFont : LayoutProperty<std::vector<std::string>> {
     static std::vector<std::string> defaultValue() { return { "Open Sans Regular", "Arial Unicode MS Regular" }; }
 };
 
-struct TextSize : LayoutProperty<float> {
+struct TextSize : DataDrivenLayoutProperty<float> {
     static constexpr const char * key = "text-size";
     static float defaultValue() { return 16; }
 };
diff --git a/src/mbgl/style/paint_property_binder.hpp b/src/mbgl/style/paint_property_binder.hpp
index 7e44b509a1..bf98e6ef9a 100644
--- a/src/mbgl/style/paint_property_binder.hpp
+++ b/src/mbgl/style/paint_property_binder.hpp
@@ -26,16 +26,12 @@ inline std::array<float, 1> attributeValue(float v) {
     uses 8-bit precision for each color component, for each float we use the upper 8
     bits for one component (e.g. (color.r * 255) * 256), and the lower 8 for another.
     
-    Also note:
-     - Colors come in as floats 0..1, so we scale by 255.
-     - Casting the scaled values to ints is important: without doing this, e.g., the
-       fractional part of the `r` component would corrupt the lower-8 bits of the encoded
-       value, which must be reserved for the `g` component.
+    Also note that colors come in as floats 0..1, so we scale by 255.
 */
 inline std::array<float, 2> attributeValue(const Color& color) {
     return {{
-        static_cast<float>(static_cast<uint16_t>(color.r * 255) * 256 + static_cast<uint16_t>(color.g * 255)),
-        static_cast<float>(static_cast<uint16_t>(color.b * 255) * 256 + static_cast<uint16_t>(color.a * 255))
+        static_cast<float>(mbgl::attributes::packUint8Pair(255 * color.r, 255 * color.g)),
+        static_cast<float>(mbgl::attributes::packUint8Pair(255 * color.b, 255 * color.a))
     }};
 }