diff --git a/src/Aesthetic.ts b/src/Aesthetic.ts
index f1c383d5b..98c0e4e31 100644
--- a/src/Aesthetic.ts
+++ b/src/Aesthetic.ts
@@ -609,6 +609,24 @@ abstract class OneDAesthetic extends Aesthetic {
 
 abstract class BooleanAesthetic extends Aesthetic {}
 
+
+class Opacity extends OneDAesthetic {
+  static get default_constant() {
+    return 1;
+  }
+  static get_default_domain() {
+    return [0, 10];
+  }
+  get default_domain() {
+    return [0, 10];
+  }
+  default_constant = 1;
+  get default_range(): [number, number] {
+    return [0, 1];
+  }
+  default_transform: Transform = 'linear';
+}
+
 class Size extends OneDAesthetic {
   static get default_constant() {
     return 1.5;
@@ -1035,6 +1053,11 @@ class StatefulY0 extends StatefulAesthetic<Y0> {
     return Y0;
   }
 }
+class Opacity extends StatefulAesthetic<Opacity> {
+  get Factory() {
+    return Opacity;
+  }
+}
 class StatefulSize extends StatefulAesthetic<Size> {
   get Factory() {
     return Size;
@@ -1075,6 +1098,7 @@ export const stateful_aesthetics: Record<
   y: StatefulY,
   y0: StatefulY0,
   size: StatefulSize,
+  opacity: StatefulOpacity,
   jitter_speed: StatefulJitter_speed,
   jitter_radius: StatefulJitter_radius,
   color: StatefulColor,
diff --git a/src/glsl/general.vert b/src/glsl/general.vert
index abd12cf1a..a8f292661 100644
--- a/src/glsl/general.vert
+++ b/src/glsl/general.vert
@@ -72,7 +72,7 @@ bool a_last_color_is_constant;
 /*
 python code to generate what follows.
 def autogenerate_code():
-  ks = ["x", "y", "jitter_radius", "jitter_speed", "size", "filter1", "filter2", "x0", "y0"]
+  ks = ["x", "y", "jitter_radius", "jitter_speed", "size", "opacity", "filter1", "filter2", "x0", "y0"]
   times = ["", "last_"]
   print("""
   //  BEGIN AUTOGENERATED. DO NOT EDIT. 
@@ -196,14 +196,14 @@ autogenerate_code()
   bool a_last_jitter_speed_is_constant;
       
 
-  uniform float u_size_buffer_num;
-  uniform float u_size_constant;
-  uniform float u_size_transform;
-  uniform vec2 u_size_domain;
-  uniform vec2 u_size_range;
-  uniform float u_size_map_position;
+  uniform float u_size_buffer_num; // ie where to find the vlaue of size within the buffer
+  uniform float u_size_constant; // default
+  uniform float u_size_transform; // eg "log"
+  uniform vec2 u_size_domain; // eg [1, 100]
+  uniform vec2 u_size_range; 
+  uniform float u_size_map_position; // maps the pixel buffer of categorical variables to their value/encoding(?)
   float a_size;
-  bool a_size_is_constant;
+  bool a_size_is_constant; // use constant?
       
 
   uniform float u_last_size_buffer_num;
@@ -310,6 +310,7 @@ highp float ix_to_random(in float ix, in float seed) {
 
 
 // The fill color.
+// NOTE: these varying's get passed to through fragment shader
 varying vec4 fill;
 varying float point_size;
 
@@ -915,6 +916,7 @@ void main() {
     }
 
     if (u_size_buffer_num > -0.5) {
+      // look:
       a_size = get_buffer(u_size_buffer_num);
       a_size_is_constant = false;
     } else {
@@ -995,6 +997,7 @@ void main() {
     }
 //  END AUTOGENERATED. DO NOT EDIT ABOVE. 
 // ------------------------------------------------    
+// NOTE: things with gl_ prefix are magic variables that persist
   gl_PointSize = 1.;
 
   if (u_color_buffer_num > -0.5) {
@@ -1146,6 +1149,7 @@ void main() {
     return;
   }
 
+// note:
   float size_multiplier = texture_float_lookup(
     u_size_domain,
     u_size_range,
@@ -1156,6 +1160,22 @@ void main() {
     u_last_size_domain, u_last_size_range, u_last_size_transform, a_last_size,
     u_last_size_map_position);
 
+ // we're transitioning between previos & new value via ease
+  size_multiplier = u_base_size * 
+     mix(last_size_multiplier, size_multiplier, ease);
+
+// CONVERT TO OPACITY
+  float size_multiplier = texture_float_lookup(
+    u_size_domain,
+    u_size_range,
+    u_size_transform, a_size,
+    u_size_map_position);
+
+  float last_size_multiplier = texture_float_lookup(
+    u_last_size_domain, u_last_size_range, u_last_size_transform, a_last_size,
+    u_last_size_map_position);
+
+ // we're transitioning between previos & new value via ease
   size_multiplier = u_base_size * 
      mix(last_size_multiplier, size_multiplier, ease);
   
@@ -1232,6 +1252,8 @@ void main() {
     run_color_fill(ease);
   }
 //  gl_PointSize = 2.1;
+// toward the end we need to update this somethign like this:
+  fill.a = fill.a * opacityMultiplier
   point_size = gl_PointSize;
 /*  if (u_use_glyphset > 0. && point_size > 5.0) {
     float random_letter = floor(64. * ix_to_random(ix, 1.3));
diff --git a/src/regl_rendering.ts b/src/regl_rendering.ts
index 3644c1abf..e78b23009 100644
--- a/src/regl_rendering.ts
+++ b/src/regl_rendering.ts
@@ -835,6 +835,7 @@ export class ReglRenderer<T extends Tile> extends Renderer {
           viewportWidth / viewportHeight,
         //@ts-ignore
         u_zoom_balance: regl.prop('zoom_balance'),
+        // global vs computed size (I think Ben said)
         u_base_size: (_, { point_size }) => point_size,
         u_maxix: (_, { max_ix }) => max_ix,
         u_alpha: (_, { alpha }) => alpha,
@@ -887,6 +888,7 @@ export class ReglRenderer<T extends Tile> extends Renderer {
       'x0',
       'y0',
       'jitter_speed',
+      'opacity',
       'size',
       'filter',
       'filter2',
@@ -956,6 +958,7 @@ export class ReglRenderer<T extends Tile> extends Renderer {
       'x0',
       'y0',
       'size',
+      'opacity',
       'jitter_radius',
       'jitter_speed',
       'filter',