Simple shader fixes. (#8991)

1. Pass current camera offset to shader, so shader have access to the global coordinates
2. Pass animation timer to fragment shader. C++ code is already there, just wasn't declared in the shader
3. Delay animation timer wrap-around (from 100s to about 16 minutes)

client/shaders/nodes_shader/opengl_vertex.glsl

@@ -4,9 +4,17 @@ uniform mat4 mWorld;
 // Color of the light emitted by the sun.
 uniform vec3 dayLight;
 uniform vec3 eyePosition;
+
+// The cameraOffset is the current center of the visible world.
+uniform vec3 cameraOffset;
 uniform float animationTimer;
 
 varying vec3 vPosition;
+// World position in the visible world (i.e. relative to the cameraOffset.)
+// This can be used for many shader effects without loss of precision.
+// If the absolute position is required it can be calculated with
+// cameraOffset + worldPosition (for large coordinates the limits of float
+// precision must be considered).
 varying vec3 worldPosition;
 
 varying vec3 eyeVec;