Ortho shading fixes (#6453)

shaders/src/getters.fs

@@ -54,6 +54,10 @@ vec3 getWorldViewVector() {
     return shading_view;
 }
 
+bool isPerspectiveProjection() {
+    return frameUniforms.clipFromViewMatrix[2].w != 0.0;
+}
+
 /** @public-api */
 vec3 getWorldNormalVector() {
     return shading_normal;

shaders/src/shading_parameters.fs

@@ -33,7 +33,13 @@ void computeShadingParams() {
 #endif
 
     shading_position = vertex_worldPosition.xyz;
-    shading_view = normalize(frameUniforms.cameraPosition - shading_position);
+
+    // With perspective camera, the view vector is cast from the fragment pos to the eye position,
+    // With ortho camera, however, the view vector is the same for all fragments:
+    shading_view = isPerspectiveProjection() ?
+        (frameUniforms.cameraPosition - shading_position) :
+        frameUniforms.worldFromViewMatrix[2].xyz; // ortho camera backward dir
+    shading_view = normalize(shading_view);
 
     // we do this so we avoid doing (matrix multiply), but we burn 4 varyings:
     //    p = clipFromWorldMatrix * shading_position;