[core] Use separate attribute component for line normals

Selective cherry pick of 822df3dd514ec3d05f876e6746cb8ba6348ac89d

1 files changed, 9 insertions, 10 deletions

diff --git a/src/mbgl/shaders/line_sdf.cpp b/src/mbgl/shaders/line_sdf.cpp
index b37bf688d4..24b7153c7f 100644
--- a/src/mbgl/shaders/line_sdf.cpp
+++ b/src/mbgl/shaders/line_sdf.cpp
@@ -23,7 +23,7 @@ const char* line_sdf::vertexSource = R"MBGL_SHADER(
 // Retina devices need a smaller distance to avoid aliasing.
 #define ANTIALIASING 1.0 / DEVICE_PIXEL_RATIO / 2.0
 
-attribute vec2 a_pos;
+attribute vec3 a_pos_normal;
 attribute vec4 a_data;
 
 uniform mat4 u_matrix;
@@ -116,20 +116,22 @@ void main() {
     float a_direction = mod(a_data.z, 4.0) - 1.0;
     float a_linesofar = (floor(a_data.z / 4.0) + a_data.w * 64.0) * LINE_DISTANCE_SCALE;
 
-    // We store the texture normals in the most insignificant bit
-    // transform y so that 0 => -1 and 1 => 1
+    vec2 pos = a_pos_normal.xy;
+
+    // transform y normal so that 0 => -1 and 1 => 1
     // In the texture normal, x is 0 if the normal points straight up/down and 1 if it's a round cap
     // y is 1 if the normal points up, and -1 if it points down
-    mediump vec2 normal = mod(a_pos, 2.0);
+    mediump vec2 normal = unpack_float(a_pos_normal.z);
     normal.y = sign(normal.y - 0.5);
+
     v_normal = normal;
 
-    // these transformations used to be applied in the JS and native code bases. 
-    // moved them into the shader for clarity and simplicity. 
+    // these transformations used to be applied in the JS and native code bases.
+    // moved them into the shader for clarity and simplicity.
     gapwidth = gapwidth / 2.0;
     float width = u_width / 2.0;
     offset = -1.0 * offset;
- 
+
     float inset = gapwidth + (gapwidth > 0.0 ? ANTIALIASING : 0.0);
     float outset = gapwidth + width * (gapwidth > 0.0 ? 2.0 : 1.0) + ANTIALIASING;
 
@@ -145,9 +147,6 @@ void main() {
     mediump float t = 1.0 - abs(u);
     mediump vec2 offset2 = offset * a_extrude * scale * normal.y * mat2(t, -u, u, t);
 
-    // Remove the texture normal bit to get the position
-    vec2 pos = floor(a_pos * 0.5);
-
     vec4 projected_extrude = u_matrix * vec4(dist / u_ratio, 0.0, 0.0);
     gl_Position = u_matrix * vec4(pos + offset2 / u_ratio, 0.0, 1.0) + projected_extrude;