[core] Implement data-driven styling for {text,icon}-{color,opacity,halo-color,halo-blur,halo-width} (#7939)

* Add symbol dds attributes and adapt style code generation

* Update to mapbox-gl-js/master

* Refactor SymbolFeature as a subclass of GeometryTileFeature

Prepares for enabling DDS on symbol paint properties by allowing the
SymbolFeatures, which we keep around after constructing SymbolLayout,
to be used in evaluating data-driven paint properties later in the
layout process.

* Draft approach for splitting icon/text paint properties

The `Program` types are set up to bind GL attributes to each of the
data-driven paint properties specified in the `PaintProperties` type
provided.  Since `SymbolPaintProperties` specifies both `Text*` and
`Icon*` properties, the symbolIcon, symbolIconSDF, and symbolGlyph
programs each attempt to bind roughly double the number of attributes
that they actually need.

This change addresses this by:
- Adding the more specific `IconPaintProperties` and `TextPaintProperties` types, which are subsets of the full `SymbolPaintProperties`.
- The symbol layer continues to use its `SymbolPaintProperties paint` member to track layer property state, but it provides helpers that construct objects of each the specific `{Icon,Text}PaintProperties::Evaluated` type, for use by the painter.
- The three symbol programs instantiate `Program<>` using the appropriate `{Icon,Text}PaintProperties` type.

* check in generated style code

* Populate paint buffers for symbol DDS properties

* Address first round of review comments

* Refactor VectorTile{Layer,Feature} to explicitly share data

* Update submodule

1 files changed, 56 insertions, 7 deletions

diff --git a/src/mbgl/shaders/symbol_sdf.cpp b/src/mbgl/shaders/symbol_sdf.cpp
index 7554597893..e087242bf8 100644
--- a/src/mbgl/shaders/symbol_sdf.cpp
+++ b/src/mbgl/shaders/symbol_sdf.cpp
@@ -68,6 +68,26 @@ attribute vec2 a_offset;
 attribute vec2 a_texture_pos;
 attribute vec4 a_data;
 
+uniform lowp float a_fill_color_t;
+attribute lowp vec4 a_fill_color_min;
+attribute lowp vec4 a_fill_color_max;
+varying lowp vec4 fill_color;
+uniform lowp float a_halo_color_t;
+attribute lowp vec4 a_halo_color_min;
+attribute lowp vec4 a_halo_color_max;
+varying lowp vec4 halo_color;
+uniform lowp float a_opacity_t;
+attribute lowp float a_opacity_min;
+attribute lowp float a_opacity_max;
+varying lowp float opacity;
+uniform lowp float a_halo_width_t;
+attribute lowp float a_halo_width_min;
+attribute lowp float a_halo_width_max;
+varying lowp float halo_width;
+uniform lowp float a_halo_blur_t;
+attribute lowp float a_halo_blur_min;
+attribute lowp float a_halo_blur_max;
+varying lowp float halo_blur;
 
 // matrix is for the vertex position.
 uniform mat4 u_matrix;
@@ -87,6 +107,12 @@ varying vec2 v_fade_tex;
 varying float v_gamma_scale;
 
 void main() {
+    fill_color = mix(a_fill_color_min, a_fill_color_max, a_fill_color_t);
+    halo_color = mix(a_halo_color_min, a_halo_color_max, a_halo_color_t);
+    opacity = mix(a_opacity_min, a_opacity_max, a_opacity_t);
+    halo_width = mix(a_halo_width_min, a_halo_width_max, a_halo_width_t);
+    halo_blur = mix(a_halo_blur_min, a_halo_blur_max, a_halo_blur_t);
+
     vec2 a_tex = a_texture_pos.xy;
     mediump float a_labelminzoom = a_data[0];
     mediump vec2 a_zoom = a_data.pq;
@@ -163,24 +189,47 @@ precision mediump float;
 #endif
 
 #endif
+#define SDF_PX 8.0
+#define EDGE_GAMMA 0.105/DEVICE_PIXEL_RATIO
+
+uniform bool u_is_halo;
+varying lowp vec4 fill_color;
+varying lowp vec4 halo_color;
+varying lowp float opacity;
+varying lowp float halo_width;
+varying lowp float halo_blur;
+
 uniform sampler2D u_texture;
 uniform sampler2D u_fadetexture;
-uniform lowp vec4 u_color;
-uniform lowp float u_opacity;
-uniform lowp float u_buffer;
-uniform highp float u_gamma;
+uniform lowp float u_font_scale;
+uniform highp float u_gamma_scale;
 
 varying vec2 v_tex;
 varying vec2 v_fade_tex;
 varying float v_gamma_scale;
 
 void main() {
+    
+    
+    
+    
+    
+
+    lowp vec4 color = fill_color;
+    lowp float gamma = EDGE_GAMMA / u_gamma_scale;
+    lowp float buff = (256.0 - 64.0) / 256.0;
+    if (u_is_halo) {
+        color = halo_color;
+        gamma = (halo_blur * 1.19 / SDF_PX + EDGE_GAMMA) / u_gamma_scale;
+        buff = (6.0 - halo_width / u_font_scale) / SDF_PX;
+    }
+
     lowp float dist = texture2D(u_texture, v_tex).a;
     lowp float fade_alpha = texture2D(u_fadetexture, v_fade_tex).a;
-    highp float gamma = u_gamma * v_gamma_scale;
-    highp float alpha = smoothstep(u_buffer - gamma, u_buffer + gamma, dist) * fade_alpha;
+    highp float gamma_scaled = gamma * v_gamma_scale;
+    highp float alpha = smoothstep(buff - gamma_scaled, buff + gamma_scaled, dist) * fade_alpha;
 
-    gl_FragColor = u_color * (alpha * u_opacity);
+    gl_FragColor = color * (alpha * opacity);
 
 #ifdef OVERDRAW_INSPECTOR
     gl_FragColor = vec4(1.0);