[core] Update circle shader code

Ported the following patches:
 - [convert mat4 exMatrix to a vec2 extrudeScale](mapbox/mapbox-gl-shaders@a8d549b)
 - [Enabled data-driven styling for circle-radius](mapbox/mapbox-gl-shaders@4356e41)
 - [Reduce shader boilerplate, refactor "Bucket"](mapbox/mapbox-gl-shaders@7d3da8f)

package.json

@@ -19,7 +19,7 @@
   "devDependencies": {
     "aws-sdk": "^2.3.5",
     "express": "^4.11.1",
-    "mapbox-gl-shaders": "mapbox/mapbox-gl-shaders#4a567b438be303fbbf13e5ddf49d72d8debd811d",
+    "mapbox-gl-shaders": "mapbox/mapbox-gl-shaders#13aad76282c1b6c4d38fd46f373325dfec69ab01",
     "mapbox-gl-test-suite": "mapbox/mapbox-gl-test-suite#b3441d9a285ffbe9b876677acb13d7df07e5b975",
     "node-gyp": "^3.3.1",
     "request": "^2.72.0",

src/mbgl/renderer/painter.cpp

@@ -100,6 +100,8 @@ void Painter::render(const Style& style, const FrameData& frame_, SpriteAtlas& a
     // The extrusion matrix.
     matrix::ortho(extrudeMatrix, 0, state.getWidth(), state.getHeight(), 0, 0, -1);
 
+    extrudeScale = {{ (2.0f / state.getWidth()) * state.getAltitude(), -2.0f / state.getHeight() * state.getAltitude() }};
+
     // The native matrix is a 1:1 matrix that paints the coordinates at the
     // same screen position as the vertex specifies.
     matrix::identity(nativeMatrix);

src/mbgl/renderer/painter.hpp

@@ -158,6 +158,8 @@ class Painter : private util::noncopyable {
     mat4 nativeMatrix;
     mat4 extrudeMatrix;
 
+    std::array<float, 2> extrudeScale;
+
     // used to composite images and flips the geometry upside down
     const mat4 flipMatrix = []{
         mat4 flip;

src/mbgl/renderer/painter_circle.cpp

@@ -33,11 +33,12 @@ void Painter::renderCircle(CircleBucket& bucket,
     config.program = circleShader->getID();
 
     circleShader->u_matrix = vtxMatrix;
-    circleShader->u_exmatrix = extrudeMatrix;
+    circleShader->u_extrude_scale = extrudeScale;
+    circleShader->u_devicepixelratio = frame.pixelRatio;
     circleShader->u_color = properties.circleColor;
-    circleShader->u_opacity = properties.circleOpacity;
+    circleShader->u_radius = properties.circleRadius;
     circleShader->u_blur = std::max<float>(properties.circleBlur, antialiasing);
-    circleShader->u_size = properties.circleRadius;
+    circleShader->u_opacity = properties.circleOpacity;
 
     bucket.drawCircles(*circleShader, glObjectStore);
 }

src/mbgl/shader/circle_shader.hpp

@@ -11,12 +11,13 @@ class CircleShader : public Shader {
 
     void bind(GLbyte *offset) final;
 
-    UniformMatrix<4>                 u_matrix   = {"u_matrix",   *this};
-    UniformMatrix<4>                 u_exmatrix = {"u_exmatrix", *this};
-    Uniform<std::array<GLfloat, 4>>  u_color    = {"u_color",    *this};
-    Uniform<GLfloat>                 u_opacity  = {"u_opacity",  *this};
-    Uniform<GLfloat>                 u_size     = {"u_size",     *this};
-    Uniform<GLfloat>                 u_blur     = {"u_blur",     *this};
+    UniformMatrix<4>                 u_matrix           = {"u_matrix",           *this};
+    Uniform<std::array<GLfloat, 2>>  u_extrude_scale    = {"u_extrude_scale",    *this};
+    Uniform<GLfloat>                 u_devicepixelratio = {"u_devicepixelratio", *this};
+    Uniform<std::array<GLfloat, 4>>  u_color            = {"u_color",            *this};
+    Uniform<GLfloat>                 u_radius           = {"u_radius",           *this};
+    Uniform<GLfloat>                 u_blur             = {"u_blur",             *this};
+    Uniform<GLfloat>                 u_opacity          = {"u_opacity",          *this};
 };
 
 } // namespace mbgl