fix(point-layer): adjust shift bits in vertex compression

src/geom/buffer/point/circleBuffer.js

@@ -1,10 +1,7 @@
 import { packUint8ToFloat } from '../../../util/vertex-compress';
 
-// const LEFT_SHIFT2 = 4.0;
-// const LEFT_SHIFT4 = 16.0;
-const LEFT_SHIFT8 = 256.0;
-const LEFT_SHIFT10 = 1024.0;
-// const LEFT_SHIFT12 = 4096.0;
+const LEFT_SHIFT18 = 262144.0;
+const LEFT_SHIFT20 = 1048576.0;
 
 export default function circleBuffer(layerData) {
   const index = [];
@@ -29,14 +26,15 @@ export default function circleBuffer(layerData) {
       [ 1, 1 ],
       [ -1, 1 ]
     ].forEach(extrude => {
-      // vec4(color, color, (8-bit size, 4-bit extrude), id)
+      // vec4(color, color, (4-bit extrude, 16-bit size), id)
       aPackedData.push(
         ...packedColor,
-        size + (extrude[0] + 1) * LEFT_SHIFT8 + (extrude[1] + 1) * LEFT_SHIFT10,
+        (extrude[0] + 1) * LEFT_SHIFT20 + (extrude[1] + 1) * LEFT_SHIFT18 + size,
         id
       );
     });
 
+    // TODO：如果使用相对瓦片坐标，还可以进一步压缩
     aPosition.push(...coordinates, ...coordinates, ...coordinates, ...coordinates);
     index.push(...[ 0, 1, 2, 0, 2, 3 ].map(n => n + i * 4));
   });

src/geom/shader/circle_vert.glsl

@@ -17,20 +17,20 @@ void main() {
   // unpack picking_id
   float picking_id = a_packed_data.w;
 
-  // unpack data(radius(8-bit), extrude(4-bit))
+  // unpack data(extrude(4-bit), radius(16-bit))
   float compressed = a_packed_data.z;
 
   // extrude(4-bit)
   vec2 extrude;
-  extrude.y = floor(compressed * SHIFT_RIGHT10);
-  compressed -= extrude.y * SHIFT_LEFT10;
-  extrude.y = extrude.y - 1.;
-
-  extrude.x = floor(compressed * SHIFT_RIGHT8);
-  compressed -= extrude.x * SHIFT_LEFT8;
+  extrude.x = floor(compressed * SHIFT_RIGHT20);
+  compressed -= extrude.x * SHIFT_LEFT20;
   extrude.x = extrude.x - 1.;
 
-  // radius(8-bit)
+  extrude.y = floor(compressed * SHIFT_RIGHT18);
+  compressed -= extrude.y * SHIFT_LEFT18;
+  extrude.y = extrude.y - 1.;
+
+  // radius(16-bit)
   float radius = compressed;
   v_radius = radius;
 

src/geom/shader/shaderChunks/decode.glsl

@@ -1,11 +1,7 @@
-#define SHIFT_RIGHT2 0.25
-#define SHIFT_RIGHT4 0.0625
-#define SHIFT_RIGHT8 1.0 / 256.0
-#define SHIFT_RIGHT10 1.0 / 1024.0
-#define SHIFT_LEFT2 4.0
-#define SHIFT_LEFT4 16.0
-#define SHIFT_LEFT8 256.0
-#define SHIFT_LEFT10 1024.0
+#define SHIFT_RIGHT18 1.0 / 262144.0
+#define SHIFT_RIGHT20 1.0 / 1048576.0
+#define SHIFT_LEFT18 262144.0
+#define SHIFT_LEFT20 1048576.0
 
 vec2 unpack_float(const float packedValue) {
   int packedIntValue = int(packedValue);