Fix edge and polyline z

common/changes/@bentley/imodeljs-frontend/fix-edge-and-polyline-z_2021-03-29-16-18.json

@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "@bentley/imodeljs-frontend",
+      "comment": "fixed z for edges and polylines when extended behind the eye",
+      "type": "none"
+    }
+  ],
+  "packageName": "@bentley/imodeljs-frontend",
+  "email": "36053767+MarcNeely@users.noreply.github.com"
+}

core/frontend/src/render/webgl/glsl/Edge.ts

@@ -16,7 +16,7 @@ import { addShaderFlags } from "./Common";
 import { addWhiteOnWhiteReversal } from "./Fragment";
 import { addAdjustWidth, addLineCode } from "./Polyline";
 import { octDecodeNormal } from "./Surface";
-import { addLineWeight, addModelViewMatrix, addNormalMatrix, addProjectionMatrix } from "./Vertex";
+import { addLineWeight, addModelViewMatrix, addModelViewProjectionMatrix, addNormalMatrix, addProjectionMatrix } from "./Vertex";
 import { addModelToWindowCoordinates, addViewport } from "./Viewport";
 
 const decodeEndPointAndQuadIndices = `
@@ -62,16 +62,15 @@ const computePosition = `
   vec4  other = g_otherPos;
   float miterAdjust = 0.0;
   float weight = computeLineWeight();
-  float clipDist;
 
-  g_windowPos = modelToWindowCoordinates(rawPos, other, clipDist);
+  vec4 pos;
+  g_windowPos = modelToWindowCoordinates(rawPos, other, pos, v_eyeSpace);
   if (g_windowPos.w == 0.0) // Clipped out.
     return g_windowPos;
 
-  vec4 clipPos = rawPos + clipDist * (other - rawPos);
-  vec4 pos = MAT_MVP * clipPos;
-
-  vec4 projOther = modelToWindowCoordinates(other, rawPos, clipDist);
+  vec4 otherPos;
+  vec3 otherMvPos;
+  vec4 projOther = modelToWindowCoordinates(other, rawPos, otherPos, otherMvPos);
 
   g_windowDir = projOther.xy - g_windowPos.xy;
 
@@ -117,9 +116,10 @@ function createBase(isSilhouette: boolean, instanced: IsInstanced, isAnimated: I
   vert.addGlobal("lineCodeEyePos", VariableType.Vec4);
   vert.addGlobal("lineCodeDist", VariableType.Float, "0.0");
 
-  addModelToWindowCoordinates(vert); // adds u_mvp, u_viewportTransformation
+  addModelToWindowCoordinates(vert); // adds u_mvp, u_viewportTransformation, and sets g_eyeSpace
   addProjectionMatrix(vert);
   addLineCode(builder, lineCodeArgs);
+  builder.addVarying("v_eyeSpace", VariableType.Vec3);
   vert.set(VertexShaderComponent.ComputePosition, computePosition);
   builder.addVarying("v_lnInfo", VariableType.Vec4);
   addAdjustWidth(vert);
@@ -131,6 +131,7 @@ function createBase(isSilhouette: boolean, instanced: IsInstanced, isAnimated: I
 
   if (isSilhouette) {
     addNormalMatrix(vert);
+    addModelViewProjectionMatrix(vert);
     vert.set(VertexShaderComponent.CheckForEarlyDiscard, checkForSilhouetteDiscard);
     vert.addFunction(octDecodeNormal);
   }

core/frontend/src/render/webgl/glsl/Polyline.ts

@@ -196,6 +196,7 @@ function addCommon(prog: ProgramBuilder) {
   addLineWeight(vert);
 
   vert.addGlobal("miterAdjust", VariableType.Float, "0.0");
+  prog.addVarying("v_eyeSpace", VariableType.Vec3);
   vert.set(VertexShaderComponent.ComputePosition, computePosition);
   prog.addVarying("v_lnInfo", VariableType.Vec4);
   addAdjustWidth(vert);
@@ -232,14 +233,11 @@ const computePosition = `
   v_lnInfo = vec4(0.0, 0.0, 0.0, 0.0);  // init and set flag to false
 
   vec4 next = g_nextPos;
-  float clipDist;
-  g_windowPos = modelToWindowCoordinates(rawPos, next, clipDist);
+  vec4 pos;
+  g_windowPos = modelToWindowCoordinates(rawPos, next, pos, v_eyeSpace);
   if (g_windowPos.w == 0.0)
     return g_windowPos;
 
-  vec4 clipPos = rawPos + clipDist * (next - rawPos);
-  vec4 pos = MAT_MVP * clipPos;
-
   float param = a_param;
   float weight = computeLineWeight();
   float scale = 1.0, directionScale = 1.0;
@@ -257,7 +255,9 @@ const computePosition = `
     param -= kNegatePerp;
   }
 
-  vec4 projNext = modelToWindowCoordinates(next, rawPos, clipDist);
+  vec4 otherPos;
+  vec3 otherMvPos;
+  vec4 projNext = modelToWindowCoordinates(next, rawPos, otherPos, otherMvPos);
   g_windowDir = projNext.xy - g_windowPos.xy;
 
   if (param < kJointBase) {
@@ -269,7 +269,7 @@ const computePosition = `
   if (kNone != param) {
     vec2 delta = vec2(0.0);
     vec4 prev   = g_prevPos;
-    vec4 projPrev = modelToWindowCoordinates(prev, rawPos, clipDist);
+    vec4 projPrev = modelToWindowCoordinates(prev, rawPos, otherPos, otherMvPos);
     vec2 prevDir   = g_windowPos.xy - projPrev.xy;
     float thisLength = sqrt(g_windowDir.x * g_windowDir.x + g_windowDir.y * g_windowDir.y);
     const float s_minNormalizeLength = 1.0E-5;  // avoid normalizing zero length vectors.

core/frontend/src/render/webgl/glsl/Viewport.ts

@@ -8,7 +8,7 @@
 
 import { ShaderBuilder, VariableType, VertexShaderBuilder } from "../ShaderBuilder";
 import { addRenderPass } from "./RenderPass";
-import { addModelViewProjectionMatrix } from "./Vertex";
+import { addModelViewMatrix, addProjectionMatrix } from "./Vertex";
 
 /** @internal */
 export function addViewport(shader: ShaderBuilder) {
@@ -29,32 +29,36 @@ export function addViewportTransformation(shader: ShaderBuilder) {
 }
 
 const modelToWindowCoordinates = `
-vec4 modelToWindowCoordinates(vec4 position, vec4 next, out float clipDist) {
-  clipDist = 0.0;
+vec4 modelToWindowCoordinates(vec4 position, vec4 next, out vec4 clippedMvpPos, out vec3 clippedMvPos) {
   if (kRenderPass_ViewOverlay == u_renderPass || kRenderPass_Background == u_renderPass) {
-    vec4 q = MAT_MVP * position;
+    vec4 q = MAT_MV * position;
+    clippedMvPos = q.xyz;
+    q = u_proj * q;
+    clippedMvpPos = q;
     q.xyz /= q.w;
     q.xyz = (u_viewportTransformation * vec4(q.xyz, 1.0)).xyz;
     return q;
   }
 
   // Negative values are in front of the camera (visible).
   float s_maxZ = -u_frustum.x;            // use -near (front) plane for segment drop test since u_frustum's near & far are pos.
-  vec4  q = MAT_MV * position;              // eye coordinates.
+  vec4  q = MAT_MV * position;            // eye coordinates.
   vec4  n = MAT_MV * next;
 
   if (q.z > s_maxZ) {
     if (n.z > s_maxZ)
-      return vec4(0.0, 0.0,  1.0, 0.0);   // Entire segment behind eye.
+      return vec4(0.0, 0.0, 1.0, 0.0);    // Entire segment behind front clip plane.
 
-    clipDist = (s_maxZ - q.z) / (n.z - q.z);
+    float t = (s_maxZ - q.z) / (n.z - q.z);
 
-    q.x += clipDist * (n.x - q.x);
-    q.y += clipDist * (n.y - q.y);
-    q.z = s_maxZ;                       // q.z + (s_maxZ - q.z) * (s_maxZ - q.z) / n.z - q.z
+    q.x += t * (n.x - q.x);
+    q.y += t * (n.y - q.y);
+    q.z = s_maxZ;                         // q.z + (s_maxZ - q.z) / (n.z - q.z) * (n.z - q.z) = s_maxZ
   }
 
+  clippedMvPos = q.xyz;
   q = u_proj * q;
+  clippedMvpPos = q;
   q.xyz /= q.w;                           // normalized device coords
   q.xyz = (u_viewportTransformation * vec4(q.xyz, 1.0)).xyz; // window coords
   return q;
@@ -63,7 +67,8 @@ vec4 modelToWindowCoordinates(vec4 position, vec4 next, out float clipDist) {
 
 /** @internal */
 export function addModelToWindowCoordinates(vert: VertexShaderBuilder) {
-  addModelViewProjectionMatrix(vert);
+  addModelViewMatrix(vert);
+  addProjectionMatrix(vert);
   addViewportTransformation(vert);
   addRenderPass(vert);
   vert.addFunction(modelToWindowCoordinates);