fix DVR with orthographic projection

src/mol-gl/shader/direct-volume.frag.ts

@@ -1,5 +1,5 @@
 /**
- * Copyright (c) 2017-2020 mol* contributors, licensed under MIT, See LICENSE file for more info.
+ * Copyright (c) 2017-2021 mol* contributors, licensed under MIT, See LICENSE file for more info.
  *
  * @author Alexander Rose <alexander.rose@weirdbyte.de>
  * @author Michael Krone <michael.krone@uni-tuebingen.de>
@@ -258,7 +258,7 @@ vec4 raymarch(vec3 startLoc, vec3 step, vec3 rayDir) {
                     #ifdef enabledFragDepth
                         return packDepthToRGBA(gl_FragDepthEXT);
                     #else
-                        return packDepthToRGBA(gl_FragCoord.z);
+                        return packDepthToRGBA(depth);
                     #endif
                 #elif defined(dRenderVariant_color)
                     #ifdef dPackedGroup
@@ -442,8 +442,9 @@ void main () {
     vec3 step = rayDir * uStepScale;
 
     float boundingSphereNear = distance(vBoundingSphere.xyz, uCameraPosition) - vBoundingSphere.w;
-    float d = max(uNear, boundingSphereNear);
-    gl_FragColor = raymarch(uCameraPosition + (d * rayDir), step, rayDir);
+    float d = max(uNear, boundingSphereNear) - mix(0.0, distance(vOrigPos, uCameraPosition), uIsOrtho);
+    vec3 start = mix(uCameraPosition, vOrigPos, uIsOrtho) + (d * rayDir);
+    gl_FragColor = raymarch(start, step, rayDir);
 
     #if defined(dRenderVariant_pick) || defined(dRenderVariant_depth)
         // discard when nothing was hit
@@ -455,7 +456,7 @@ void main () {
         #if defined(dRenderMode_isosurface) && defined(enabledFragDepth)
             float fragmentDepth = gl_FragDepthEXT;
         #else
-            float fragmentDepth = calcDepth((uView * vec4(uCameraPosition + (d * rayDir), 1.0)).xyz);
+            float fragmentDepth = calcDepth((uModelView * vec4(start, 1.0)).xyz);
         #endif
         float preFogAlpha = clamp(preFogAlphaBlended, 0.0, 1.0);
         interior = false;

src/mol-gl/shader/direct-volume.vert.ts

@@ -1,5 +1,5 @@
 /**
- * Copyright (c) 2017-2020 mol* contributors, licensed under MIT, See LICENSE file for more info.
+ * Copyright (c) 2017-2021 mol* contributors, licensed under MIT, See LICENSE file for more info.
  *
  * @author Alexander Rose <alexander.rose@weirdbyte.de>
  * @author Michael Krone <michael.krone@uni-tuebingen.de>
@@ -43,7 +43,7 @@ void main() {
 
     gl_Position = uProjection * mvPosition;
 
-    // move z position to near clip plane
-    gl_Position.z = gl_Position.w - 0.0001;
+    // move z position to near clip plane (but not too close to get precision issues)
+    gl_Position.z = gl_Position.w - 0.01;
 }
 `;