Enabled data-driven styling for circle-radius

circle.fragment.glsl

@@ -4,8 +4,9 @@ uniform lowp float u_blur;
 
 varying lowp vec4 v_color;
 varying vec2 v_extrude;
+varying lowp float v_antialiasblur;
 
 void main() {
-    float t = smoothstep(1.0 - u_blur, 1.0, length(v_extrude));
+    float t = smoothstep(1.0 - max(u_blur, v_antialiasblur), 1.0, length(v_extrude));
     gl_FragColor = v_color * (1.0 - t);
 }

circle.vertex.glsl

@@ -2,7 +2,7 @@ precision highp float;
 
 uniform mat4 u_matrix;
 uniform mat4 u_exmatrix;
-uniform mediump float u_size;
+uniform float u_devicepixelratio;
 
 attribute vec2 a_pos;
 
@@ -12,14 +12,21 @@ attribute lowp vec4 a_color;
 uniform lowp vec4 a_color;
 #endif
 
+#ifdef ATTRIBUTE_RADIUS
+attribute mediump float a_radius;
+#else
+uniform mediump float a_radius;
+#endif
+
 varying vec2 v_extrude;
 varying lowp vec4 v_color;
+varying lowp float v_antialiasblur;
 
 void main(void) {
     // unencode the extrusion vector that we snuck into the a_pos vector
     v_extrude = vec2(mod(a_pos, 2.0) * 2.0 - 1.0);
 
-    vec4 extrude = u_exmatrix * vec4(v_extrude * u_size, 0, 0);
+    vec4 extrude = u_exmatrix * vec4(v_extrude * a_radius / 10.0, 0, 0);
     // multiply a_pos by 0.5, since we had it * 2 in order to sneak
     // in extrusion data
     gl_Position = u_matrix * vec4(floor(a_pos * 0.5), 0, 1);
@@ -29,4 +36,9 @@ void main(void) {
     gl_Position += extrude * gl_Position.w;
 
     v_color = a_color / 255.0;
+
+    // This is a minimum blur distance that serves as a faux-antialiasing for
+    // the circle. since blur is a ratio of the circle's size and the intent is
+    // to keep the blur at roughly 1px, the two are inversely related.
+    v_antialiasblur = 1.0 / u_devicepixelratio / (a_radius / 10.0);
 }