dpoit, fix transparent background

src/mol-gl/shader/chunks/apply-fog.glsl.ts

@@ -12,8 +12,19 @@ if (!uTransparentBackground) {
         gl_FragColor.rgb = mix(gl_FragColor.rgb, uFogColor, fogFactor);
     }
 } else {
+    #if defined(dRenderVariant_colorDpoit)
+        if (gl_FragColor.a < 1.0) {
+            // transparent objects are blended with background color
+            gl_FragColor.a = fogAlpha;
+        } else {
+            // opaque objects need to be pre-multiplied alpha
+            gl_FragColor.rgb *= fogAlpha;
+            gl_FragColor.a = fogAlpha;
+        }
+    #else
         // pre-multiplied alpha expected for transparent background
         gl_FragColor.rgb *= fogAlpha;
         gl_FragColor.a = fogAlpha;
+    #endif
 }
 `;
\ No newline at end of file

src/mol-gl/shader/chunks/dpoit-write.glsl.ts

@@ -59,9 +59,9 @@ export const dpoit_write = `
 
             if (fragmentDepth == nearestDepth) {
                 gl_FragColor.rgb += fragColor.rgb * fragColor.a * alphaMultiplier;
-                gl_FragColor.a = (1.0 - alphaMultiplier * (1.0 - fragColor.a)) * (uTransparentBackground ? fragColor.a : 1.0);
+                gl_FragColor.a = 1.0 - alphaMultiplier * (1.0 - fragColor.a);
             } else {
-                gl_FragData[1] += vec4(fragColor.rgb, fragColor.a * (uTransparentBackground ? fragColor.a : 1.0));
+                gl_FragData[1] += fragColor;
             }
 
         } else {