Revamp map page layout and compass while removing GPS demo

miniprogram/engine/layer/gpsLayer.ts

@@ -16,7 +16,11 @@ function buildVectorCamera(scene: MapScene): CameraState {
 }
 
 export class GpsLayer implements MapLayer {
-  projectPoint(scene: MapScene): ScreenPoint {
+  projectPoint(scene: MapScene): ScreenPoint | null {
+    if (!scene.gpsPoint) {
+      return null
+    }
+
     const camera = buildVectorCamera(scene)
     const worldPoint = calibratedLonLatToWorldTile(scene.gpsPoint, scene.zoom, scene.gpsCalibration, scene.gpsCalibrationOrigin)
     return worldToScreen(camera, worldPoint, false)
@@ -29,6 +33,10 @@ export class GpsLayer implements MapLayer {
   draw(context: LayerRenderContext): void {
     const { ctx, scene, pulseFrame } = context
     const gpsScreenPoint = this.projectPoint(scene)
+    if (!gpsScreenPoint) {
+      return
+    }
+
     const pulse = this.getPulseRadius(pulseFrame)
 
     ctx.save()