shader fixes for normals and instance transforms

Author: lukemckinstry

packages/engine/Source/Scene/Model/RuntimeModelInstancingPipelineStage.js

@@ -49,6 +49,7 @@ RuntimeModelInstancingPipelineStage.process = function (
 ) {
   const shaderBuilder = renderResources.shaderBuilder;
   shaderBuilder.addDefine("HAS_INSTANCING");
+  shaderBuilder.addDefine("HAS_INSTANCE_MATRICES");
   shaderBuilder.addDefine(
     "USE_API_INSTANCING",
     undefined,

packages/engine/Source/Shaders/Model/ModelVS.glsl

@@ -85,7 +85,7 @@ void main()
         RuntimeModelInstancingStage(attributes, instanceModelView, instanceModelViewInverseTranspose);
 
         modelView = instanceModelView;
-        //normal = instanceModelViewInverseTranspose;
+        normal = instanceModelViewInverseTranspose;
         #else
         instancingStage(attributes);
         #endif

packages/engine/Source/Shaders/Model/RuntimeModelInstancingPipelineStageVS.glsl

@@ -14,6 +14,5 @@ void RuntimeModelInstancingStage(
     attributes.positionMC = (relativePositionMC + translateRelativeToEye).xyz;
 
     instanceModelView = czm_modelViewRelativeToEye;
-    // TODO: Normals
-    //instanceModelViewInverseTranspose = mat3(u_instance_modifiedModelView * instanceModel);
+    instanceModelViewInverseTranspose = mat3(czm_modelViewRelativeToEye * instanceModel);
 }