Merge pull request #1690 from secondlife/v-1475

secondlife/viewer#1475: Update PBR Terrain test plans

1 files changed, 19 insertions, 4 deletions

diff --git a/doc/testplans/pbr_terrain_appearance.md b/doc/testplans/pbr_terrain_appearance.md
index f6d54029b5..11b501be3a 100644
--- a/doc/testplans/pbr_terrain_appearance.md
+++ b/doc/testplans/pbr_terrain_appearance.md
@@ -1,13 +1,14 @@
 # PBR Terrain Appearance
 
-## Tiling
+## Tiling Without Texture Transforms
+
+This section assumes the PBR terrain of the current region and adjacent regions have the default texture transforms.
 
 The southwest corner of a region with PBR materials should exactly match up with the bottom left corner of the material texture(s).
 
-If two adjacent regions have the same PBR terrain settings, then:
+If two adjacent regions have the same PBR terrain settings, then there should not be seams between the two regions at their shared border.
 
-- There should not be seams between the two regions at their shared border
-- The ground should not suddenly slide beneath the avatar when moving between regions (except due to movement of the avatar, which is not covered by this test plan)
+The ground should not suddenly slide beneath the avatar when moving between two PBR terrain regions (except due to movement of the avatar, which is not covered by this test plan)
 
 ## Feature Gating
 
@@ -35,3 +36,17 @@ Availability of PBR textures varies by machine and graphics setting:
 ### PBR Alpha
 
 PBR terrain does not support materials with alpha blend or double-sided. In addition, the viewer does not make any guarantees about what will render behind the terrain if alpha is used.
+
+## PBR Terrain Texture Transforms
+
+Like PBR materials on prims, PBR terrain repeats are based on the [KHR\_texture\_transform](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_texture_transform) spec, and thus should be expected to behave the same way.
+
+The southwest corner of a region, at z=0, is the UV origin for all texture coordinates of the whole region. Unless an offset is also applied, scale and rotation of the terrain texture transforms are relative to that point.
+
+When an avatar faces north and looks down at flat ground, the textures of the materials should appear to face upright, unless a rotation is applied.
+
+If triplanar mapping is enabled, and an avatar faces an axially-aligned wall, the textures of the materials should appear to face upright, unless a rotation is applied.
+
+Textures of materials should not appear mirrored.
+
+When triplanar mapping is enabled, rotations on the axially aligned walls should apply in the same direction as they would on flat ground.