fix transparent SSAO for image rendering

CHANGELOG.md

@@ -14,6 +14,7 @@ Note that since we don't clearly distinguish between a public and private interf
 - Add more structure-based visuals to avoid too many (small) render-objects
     - `structure-intra-bond`, `structure-ellipsoid-mesh`, `structure-element-point`, `structure-element-cross`
 - Fix occupancy check using wrong index for inter-unit bond computation (@rxht, #1321)
+- Fix transparent SSAO for image rendering, e.g., volumne slices (#1332)
 
 ## [v4.8.0] - 2024-10-27
 

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

@@ -121,7 +121,7 @@ void main() {
             gl_FragColor = vec4(packIntToRGB(float(uObjectId)), 1.0);
             gl_FragData[1] = vec4(packIntToRGB(vInstance), 1.0);
             gl_FragData[2] = vec4(texture2D(tGroupTex, vUv).rgb, 1.0);
-            gl_FragData[3] = packDepthToRGBA(gl_FragCoord.z);
+            gl_FragData[3] = packDepthToRGBA(fragmentDepth);
         #else
             gl_FragColor = vColor;
             if (uPickType == 1) {
@@ -135,7 +135,11 @@ void main() {
     #elif defined(dRenderVariant_depth)
         if (imageData.a < 0.05)
             discard;
-        gl_FragColor = packDepthToRGBA(gl_FragCoord.z);
+        if (uRenderMask == MaskOpaque) {
+            gl_FragColor = packDepthToRGBA(fragmentDepth);
+        } else if (uRenderMask == MaskTransparent) {
+            gl_FragColor = packDepthWithAlphaToRGBA(fragmentDepth, imageData.a);
+        }
     #elif defined(dRenderVariant_marking)
         float marker = uMarker;
         if (uMarker == -1.0) {
@@ -146,7 +150,7 @@ void main() {
         if (uMarkingType == 1) {
             if (marker > 0.0 || imageData.a < 0.05)
                 discard;
-            gl_FragColor = packDepthToRGBA(gl_FragCoord.z);
+            gl_FragColor = packDepthToRGBA(fragmentDepth);
         } else {
             if (marker == 0.0 || imageData.a < 0.05)
                 discard;