Improve model-viewer support for lights (#626)

* Improve model-viewer support for lights

The main visible change here is that the model-viewer example supports
multiple light sources, with a basic UI for adding new light sources to
the scene, and for manipulating the ones that are there.

Along the way I also refactored the `IMaterial` decomposition to be a
bit less naive, while still only including a completely naive
Blinn-Phong implementation.

I also went ahead and spruced up the `cube.obj` file so that it has
multiple materials, although it is still a completely uninteresting
asset.

* Fixup: Windows SDK version

1 files changed, 3 insertions, 0 deletions

diff --git a/tools/gfx/model.h b/tools/gfx/model.h
index 046b9764b..b92dfda76 100644
--- a/tools/gfx/model.h
+++ b/tools/gfx/model.h
@@ -13,6 +13,9 @@ struct ModelLoader
     struct MaterialData
     {
         glm::vec3                   diffuseColor;
+        glm::vec3                   specularColor;
+        float                       specularity;
+
         RefPtr<TextureResource>     diffuseMap;
     };