This adds a new demo that leverages ImGui. It looks very similar to the
existing material_sandbox demo we have for desktop, with a few
differences:
1. Does not use FilamentApp.
2. Does not draw a shadow plane.
3. Does not use a TrueType font in ImGui. (improves load time)
4. Does not allow the user to spin the model. (will fix soon)
We now have a triumvirate of web demos with a progression in complexity:
1. triangle
2. suzanne
3. sandbox
This is a sufficient set of WebGL samples for now, at least until we
finish creating a proper JavaScript API.
This CL factors out some of the common code with the native sandbox
demo, but keeps the UI definition separate since the web demo has some
minor differences (e.g., there is no shadow plane yet).
Note that using viewport units for height was wrong; it caused a bad
aspect ratio on Android while the URL bar was visible. This is explained
in an article:
https://developers.google.com/web/updates/2016/12/url-bar-resizing
These two functions expect a vector of the same size as the
matrix's storage vectors (float4 for a mat4f for instance) which
has two major issues:
- The vector must end with 1 for homogeneous coordinates to work
- Passing a single scalar (mat4f::scale(0.5)) creates a matrix
whose diagonal is set to that scalar, thus breaking homogeneous
coordinates
With this change scale and translate expect a vector who dimensionality
is 1 less that of the matrix's underlying storage vectors. i.e. a float3
for mat4f.
