Add getUserTimeModulo() to materials

This calculates the modulo of the user time by a given value, using
the high precision user time. This is useful for animations without
having to worry about resetting the time.

docs/Materials.md.html

@@ -1331,6 +1331,7 @@ type aliases:
 **getWorldCameraPosition()**        | float3   |  Position of the camera/eye in world space
 **getTime()**                       | float    |  Current time in seconds, may be reset regularly to avoid precision loss
 **getUserTime()**                   | float4   |  Current time in seconds: `time`, `(double)time - time`, `0`, `0`
+**getUserTimeMode(float m)**        | float    |  Current time modulo m in seconds
 **getExposure()**                   | float    |  Photometric exposure of the camera
 **getEV100()**                      | float    |  [Exposure value at ISO 100](https://en.wikipedia.org/wiki/Exposure_value) of the camera
 

shaders/src/common_getters.fs

@@ -47,6 +47,10 @@ HIGHP vec4 getUserTime() {
     return frameUniforms.userTime;
 }
 
+HIGHP float getUserTimeMod(float m) {
+    return mod(mod(frameUniforms.userTime.x, m) + mod(frameUniforms.userTime.y, m), m);
+}
+
 /** @public-api */
 float getExposure() {
     return frameUniforms.exposure;