push bottom vertices of volumes at far view distances

Source/Core/GroundPolylineGeometry.js

@@ -927,8 +927,10 @@ define([
                 var vec2Index = vec2sWriteIndex + j * 2;
                 var wIndex = vec4Index + 3;
 
-                // Encode sidedness of vertex in texture coordinate normalization X
-                var sidedness = j < 4 ? 1.0 : -1.0;
+                // Encode sidedness of vertex relative to right plane in texture coordinate normalization X,
+                // whether vertex is top or bottom of volume in sign/magnitude of normalization Y.
+                var rightPlaneSide = j < 4 ? 1.0 : -1.0;
+                var topBottomSide = (j === 2 || j === 3 || j === 6 || j === 7) ? 1.0 : -1.0;
 
                 // 3D
                 Cartesian3.pack(encodedStart.high, startHiAndForwardOffsetX, vec4Index);
@@ -941,10 +943,15 @@ define([
                 startNormalAndForwardOffsetZ[wIndex] = forwardOffset.z;
 
                 Cartesian3.pack(endPlaneNormal, endNormalAndTextureCoordinateNormalizationX, vec4Index);
-                endNormalAndTextureCoordinateNormalizationX[wIndex] = texcoordNormalization3DX * sidedness;
+                endNormalAndTextureCoordinateNormalizationX[wIndex] = texcoordNormalization3DX * rightPlaneSide;
 
                 Cartesian3.pack(rightNormal, rightNormalAndTextureCoordinateNormalizationY, vec4Index);
-                rightNormalAndTextureCoordinateNormalizationY[wIndex] = texcoordNormalization3DY;
+
+                var texcoordNormalization = texcoordNormalization3DY * topBottomSide;
+                if (texcoordNormalization === 0.0 && topBottomSide < 0.0) {
+                    texcoordNormalization = Number.POSITIVE_INFINITY;
+                }
+                rightNormalAndTextureCoordinateNormalizationY[wIndex] = texcoordNormalization;
 
                 // 2D
                 if (compute2dAttributes) {
@@ -963,8 +970,13 @@ define([
                     offsetAndRight2D[vec4Index + 2] = right2D.x;
                     offsetAndRight2D[vec4Index + 3] = right2D.y;
 
-                    texcoordNormalization2D[vec2Index] = texcoordNormalization2DX * sidedness;
-                    texcoordNormalization2D[vec2Index + 1] = texcoordNormalization2DY;
+                    texcoordNormalization2D[vec2Index] = texcoordNormalization2DX * rightPlaneSide;
+
+                    texcoordNormalization = texcoordNormalization2DY * topBottomSide;
+                    if (texcoordNormalization === 0.0 && topBottomSide < 0.0) {
+                        texcoordNormalization = Number.POSITIVE_INFINITY;
+                    }
+                    texcoordNormalization2D[vec2Index + 1] = texcoordNormalization;
                 }
             }
 

Source/Scene/GroundPolylinePrimitive.js

@@ -397,7 +397,7 @@ define([
         // which causes problems when interpolating log depth from vertices.
         // So force computing and writing log depth in the fragment shader.
         // Re-enable at far distances to avoid z-fighting.
-        var vsDefines =  ['ENABLE_GL_POSITION_LOG_DEPTH_AT_HEIGHT'];
+        var vsDefines =  ['ENABLE_GL_POSITION_LOG_DEPTH_AT_HEIGHT', 'GLOBE_MINIMUM_ALTITUDE ' + frameState.mapProjection.ellipsoid.minimumRadius.toFixed(1)];
         var colorDefine = '';
         var materialShaderSource = '';
         if (defined(appearance.material)) {

Source/Shaders/PolylineShadowVolumeVS.glsl

@@ -1,6 +1,9 @@
 attribute vec3 position3DHigh;
 attribute vec3 position3DLow;
 
+// In 2D and in 3D, texture coordinate normalization component signs encodes:
+// * X sign - sidedness relative to right plane
+// * Y sign - is negative OR magnitude is greater than 1.0 if vertex is on bottom of volume
 #ifndef COLUMBUS_VIEW_2D
 attribute vec4 startHiAndForwardOffsetX;
 attribute vec4 startLoAndForwardOffsetY;
@@ -57,7 +60,8 @@ void main()
     endPlaneEC.xyz =  czm_normal * vec3(0.0, startEndNormals2D.zw);
     endPlaneEC.w = -dot(endPlaneEC.xyz, ecEnd);
 
-    v_texcoordNormalizationAndStartEcYZ.xy = vec2(abs(texcoordNormalization2D.x), texcoordNormalization2D.y);
+    v_texcoordNormalizationAndStartEcYZ.x = abs(texcoordNormalization2D.x);
+    v_texcoordNormalizationAndStartEcYZ.y = texcoordNormalization2D.y;
 
 #else // COLUMBUS_VIEW_2D
     vec3 ecStart = (czm_modelViewRelativeToEye * czm_translateRelativeToEye(startHiAndForwardOffsetX.xyz, startLoAndForwardOffsetY.xyz)).xyz;
@@ -80,7 +84,8 @@ void main()
     v_rightPlaneEC.xyz = czm_normal * rightNormalAndTextureCoordinateNormalizationY.xyz;
     v_rightPlaneEC.w = -dot(v_rightPlaneEC.xyz, ecStart);
 
-    v_texcoordNormalizationAndStartEcYZ.xy = vec2(abs(endNormalAndTextureCoordinateNormalizationX.w), rightNormalAndTextureCoordinateNormalizationY.w);
+    v_texcoordNormalizationAndStartEcYZ.x = abs(endNormalAndTextureCoordinateNormalizationX.w);
+    v_texcoordNormalizationAndStartEcYZ.y = rightNormalAndTextureCoordinateNormalizationY.w;
 
 #endif // COLUMBUS_VIEW_2D
 
@@ -105,6 +110,15 @@ void main()
     vec3 upOrDown = normalize(cross(v_rightPlaneEC.xyz, planeDirection)); // Points "up" for start plane, "down" at end plane.
     vec3 normalEC = normalize(cross(planeDirection, upOrDown));           // In practice, the opposite seems to work too.
 
+    // Extrude bottom vertices downward for far view distances, like for GroundPrimitives
+    upOrDown = cross(forwardDirectionEC, normalEC);
+    upOrDown = float(czm_sceneMode == czm_sceneMode3D) * upOrDown;
+    upOrDown = float(v_texcoordNormalizationAndStartEcYZ.y > 1.0 || v_texcoordNormalizationAndStartEcYZ.y < 0.0) * upOrDown;
+    upOrDown = min(GLOBE_MINIMUM_ALTITUDE, czm_geometricToleranceOverMeter * length(positionRelativeToEye.xyz)) * upOrDown;
+    positionEC.xyz += upOrDown;
+
+    v_texcoordNormalizationAndStartEcYZ.y = czm_branchFreeTernary(v_texcoordNormalizationAndStartEcYZ.y > 1.0, 0.0, abs(v_texcoordNormalizationAndStartEcYZ.y));
+
     // Determine distance along normalEC to push for a volume of appropriate width.
     // Make volumes about double pixel width for a conservative fit - in practice the
     // extra cost here is minimal compared to the loose volume heights.

Specs/Core/GroundPolylineGeometrySpec.js

@@ -77,7 +77,6 @@ defineSuite([
         verifyAttributeValuesIdentical(startHiAndForwardOffsetX);
         verifyAttributeValuesIdentical(startLoAndForwardOffsetY);
         verifyAttributeValuesIdentical(startNormalAndForwardOffsetZ);
-        verifyAttributeValuesIdentical(rightNormalAndTextureCoordinateNormalizationY);
         verifyAttributeValuesIdentical(startHiLo2D);
         verifyAttributeValuesIdentical(offsetAndRight2D);
         verifyAttributeValuesIdentical(startEndNormals2D);
@@ -105,6 +104,19 @@ defineSuite([
             expect(Math.sign(values[index])).toEqual(-1.0);
         }
 
+        // Expect rightNormalAndTextureCoordinateNormalizationY and texcoordNormalization2D.y to encode if the vertex is on the bottom
+        values = rightNormalAndTextureCoordinateNormalizationY.values;
+        expect(values[3] > 1.0).toBe(true);
+        expect(values[1 * 4 + 3] > 1.0).toBe(true);
+        expect(values[4 * 4 + 3] > 1.0).toBe(true);
+        expect(values[5 * 4 + 3] > 1.0).toBe(true);
+
+        values = texcoordNormalization2D.values;
+        expect(values[1] > 1.0).toBe(true);
+        expect(values[1 * 2 + 1] > 1.0).toBe(true);
+        expect(values[4 * 2 + 1] > 1.0).toBe(true);
+        expect(values[5 * 2 + 1] > 1.0).toBe(true);
+
         // Line segment geometry is encoded as:
         // - start position
         // - offset to the end position
@@ -137,9 +149,7 @@ defineSuite([
         expect(Cartesian3.equalsEpsilon(rightNormal3D, new Cartesian3(0.0, 0.0, -1.0), CesiumMath.EPSILON2)).toBe(true);
 
         var texcoordNormalizationX = endNormalAndTextureCoordinateNormalizationX.values[3];
-        var texcoordNormalizationY = rightNormalAndTextureCoordinateNormalizationY.values[3];
         expect(texcoordNormalizationX).toEqualEpsilon(1.0, CesiumMath.EPSILON3);
-        expect(texcoordNormalizationY).toEqualEpsilon(0.0, CesiumMath.EPSILON3);
 
         // 2D
         var projection = new GeographicProjection();
@@ -174,9 +184,7 @@ defineSuite([
         expect(Cartesian3.equalsEpsilon(rightNormal2D, new Cartesian3(0.0, -1.0, 0.0), CesiumMath.EPSILON2)).toBe(true);
 
         texcoordNormalizationX = texcoordNormalization2D.values[0];
-        texcoordNormalizationY = texcoordNormalization2D.values[1];
         expect(texcoordNormalizationX).toEqualEpsilon(1.0, CesiumMath.EPSILON3);
-        expect(texcoordNormalizationY).toEqualEpsilon(0.0, CesiumMath.EPSILON3);
     });
 
     it('does not generate 2D attributes when scene3DOnly is true', function() {