[core] Update sdf shader code

Ported the following patch:
- [convert mat4 exMatrix to a vec2 extrudeScale](https://github.com/mapbox/mapbox-gl-shaders/commit/a8d549b7a41540d3a99767975ff1b7b18a6010e9)

5 files changed, 28 insertions, 37 deletions

diff --git a/package.json b/package.json
index 8f2a6ec852..7620e1d9d5 100644
--- a/package.json
+++ b/package.json
@@ -19,7 +19,7 @@
   "devDependencies": {
     "aws-sdk": "^2.3.5",
     "express": "^4.11.1",
-    "mapbox-gl-shaders": "mapbox/mapbox-gl-shaders#49022d5b92c067b8659f5700a04f376d75f2950e",
+    "mapbox-gl-shaders": "mapbox/mapbox-gl-shaders#36278b864e60e1dba937a6863064c03d69526854",
     "mapbox-gl-test-suite": "mapbox/mapbox-gl-test-suite#b3441d9a285ffbe9b876677acb13d7df07e5b975",
     "node-gyp": "^3.3.1",
     "request": "^2.72.0",
diff --git a/src/mbgl/renderer/painter.cpp b/src/mbgl/renderer/painter.cpp
index d8636a9f11..1e1b37ef44 100644
--- a/src/mbgl/renderer/painter.cpp
+++ b/src/mbgl/renderer/painter.cpp
@@ -97,9 +97,7 @@ void Painter::render(const Style& style, const FrameData& frame_, SpriteAtlas& a
     // Update the default matrices to the current viewport dimensions.
     state.getProjMatrix(projMatrix);
 
-    // The extrusion matrix.
-    matrix::ortho(extrudeMatrix, 0, state.getWidth(), state.getHeight(), 0, 0, -1);
-
+    // The extrusion scale.
     const float flippedY = state.getViewportMode() == ViewportMode::FlippedY;
     extrudeScale = {{ 2.0f / state.getWidth() * state.getAltitude(),
                       (flippedY ? 2.0f : -2.0f) / state.getHeight() * state.getAltitude() }};
diff --git a/src/mbgl/renderer/painter.hpp b/src/mbgl/renderer/painter.hpp
index 6b86dfa69d..4401a95d6e 100644
--- a/src/mbgl/renderer/painter.hpp
+++ b/src/mbgl/renderer/painter.hpp
@@ -156,7 +156,6 @@ private:
 
     mat4 projMatrix;
     mat4 nativeMatrix;
-    mat4 extrudeMatrix;
 
     std::array<float, 2> extrudeScale;
 
diff --git a/src/mbgl/renderer/painter_symbol.cpp b/src/mbgl/renderer/painter_symbol.cpp
index 6f628b9d16..d19d7bc498 100644
--- a/src/mbgl/renderer/painter_symbol.cpp
+++ b/src/mbgl/renderer/painter_symbol.cpp
@@ -36,34 +36,28 @@ void Painter::renderSDF(SymbolBucket &bucket,
 {
     mat4 vtxMatrix = translatedMatrix(matrix, translate, tileID, translateAnchor);
 
-    bool skewed = rotationAlignment == RotationAlignmentType::Map;
-    mat4 exMatrix;
-    float s;
-    float gammaScale;
-
-    if (skewed) {
-        matrix::identity(exMatrix);
-        s = tileID.pixelsToTileUnits(1, state.getZoom());
-        gammaScale = 1.0f / std::cos(state.getPitch());
-    } else {
-        exMatrix = extrudeMatrix;
-        s = state.getAltitude();
-        gammaScale = 1.0f;
-        matrix::rotate_z(exMatrix, exMatrix, state.getNorthOrientationAngle());
-    }
-    const bool flippedY = !skewed && state.getViewportMode() == ViewportMode::FlippedY;
-    matrix::scale(exMatrix, exMatrix, s, flippedY ? -s : s, 1);
-
     // If layerStyle.size > bucket.info.fontSize then labels may collide
     float fontSize = paintSize;
     float fontScale = fontSize / sdfFontSize;
-    matrix::scale(exMatrix, exMatrix, fontScale, fontScale, 1.0f);
+
+    float scale = fontScale;
+    std::array<float, 2> exScale = extrudeScale;
+    bool alignedWithMap = rotationAlignment == RotationAlignmentType::Map;
+    float gammaScale = 1.0f;
+
+    if (alignedWithMap) {
+        scale *= tileID.pixelsToTileUnits(1, state.getZoom());
+        exScale.fill(scale);
+        gammaScale /= std::cos(state.getPitch());
+    } else {
+        exScale = {{ exScale[0] * scale, exScale[1] * scale }};
+    }
 
     config.program = sdfShader.getID();
     sdfShader.u_matrix = vtxMatrix;
-    sdfShader.u_exmatrix = exMatrix;
+    sdfShader.u_extrude_scale = exScale;
     sdfShader.u_texsize = texsize;
-    sdfShader.u_skewed = skewed;
+    sdfShader.u_skewed = alignedWithMap;
     sdfShader.u_texture = 0;
 
     // adjust min/max zooms for variable font sies
diff --git a/src/mbgl/shader/sdf_shader.hpp b/src/mbgl/shader/sdf_shader.hpp
index acef4d5755..c98734c0a4 100644
--- a/src/mbgl/shader/sdf_shader.hpp
+++ b/src/mbgl/shader/sdf_shader.hpp
@@ -9,17 +9,17 @@ class SDFShader : public Shader {
 public:
     SDFShader(gl::GLObjectStore&);
 
-    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<std::array<GLfloat, 2>> u_texsize     = {"u_texsize",     *this};
-    Uniform<GLfloat>                u_buffer      = {"u_buffer",      *this};
-    Uniform<GLfloat>                u_gamma       = {"u_gamma",       *this};
-    Uniform<GLfloat>                u_zoom        = {"u_zoom",        *this};
-    Uniform<GLint>                  u_skewed      = {"u_skewed",      *this};
-    Uniform<GLint>                  u_texture     = {"u_texture",     *this};
-    Uniform<GLint>                  u_fadetexture = {"u_fadetexture", *this};
+    UniformMatrix<4>                u_matrix        = {"u_matrix",        *this};
+    Uniform<std::array<GLfloat, 2>> u_extrude_scale = {"u_extrude_scale", *this};
+    Uniform<std::array<GLfloat, 4>> u_color         = {"u_color",         *this};
+    Uniform<GLfloat>                u_opacity       = {"u_opacity",       *this};
+    Uniform<std::array<GLfloat, 2>> u_texsize       = {"u_texsize",       *this};
+    Uniform<GLfloat>                u_buffer        = {"u_buffer",        *this};
+    Uniform<GLfloat>                u_gamma         = {"u_gamma",         *this};
+    Uniform<GLfloat>                u_zoom          = {"u_zoom",          *this};
+    Uniform<GLint>                  u_skewed        = {"u_skewed",        *this};
+    Uniform<GLint>                  u_texture       = {"u_texture",       *this};
+    Uniform<GLint>                  u_fadetexture   = {"u_fadetexture",   *this};
 
 protected:
     GLint a_offset = -1;