fix background occlusion handling

CHANGELOG.md

@@ -7,6 +7,7 @@ Note that since we don't clearly distinguish between a public and private interf
 ## [Unreleased]
 
 - Optimize inter unit bond compute
+- Improve SSAO for thin geometry (e.g. lines)
 
 ## [v3.35.0] - 2023-05-14
 

src/mol-gl/shader/ssao.frag.ts

@@ -114,7 +114,7 @@ void main(void) {
     vec2 selfPackedDepth = packUnitIntervalToRG(selfDepth);
 
     if (isBackground(selfDepth)) {
-        gl_FragColor = vec4(packUnitIntervalToRG(0.0), selfPackedDepth);
+        gl_FragColor = vec4(packUnitIntervalToRG(1.0), selfPackedDepth);
         return;
     }