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Computing underwater caustics accurately is a complex process: millions of individual photons are involved.
Here we simplify the computation process by making some assumptions:
Sun is directly above
floor is lit by rays emanating vertically above the point of interest: caustics will be maximal for vertical rays and will not be as visible for rays entering water sideways
for each point we calculate two refract rays, one is using vertical normal and the other is using the real normal. And we get the caustic value by compare the two refract rays, Then write the caustic value to the caustic map.
- Obj Interaction Use bounding sphere to interaction with water, without triangle test, so that performance is maintained fast and realtime.
- God Ray
Volumetric light scattering due to shadows
Use Perlin noise as a noise texture to change water height based on noise.
Pseudo random mouse click.
To complete water simulation, a gl.RGBA float texture is used to store the simulation data. It is in the format of
[height.y, normal.x, normal.z, speed.y].
In the Height Map shader, or the sphere move simulation,
height.y is updated by mouse click/sphere movement.
In the Normal Map shader,
normal.z is updated with new height information.
normal.ycan be recovered when used.
In the step simulation,
speed.y is calculated based on new height and normal information. the speed is also attenuated to eventually stop the wave pattern.
Ad the end, the texture
[height.y, normal.x, normal.z, speed.y] is passed into water mesh shaders as useful information to render out the water simualtion.
- Height Map
As you can see, the height of vertex is changed after this shader.
height.y += drag(drag is based on dist to click center)
- Normal Map
The normal is calculated and shaded correctly after this shader.
normal = cross (dHeight/dx, dHeight/dy)
- Step Simulation
The wave propagates and attenuates due to this shader.
speed.y += (averageHeight - Height)
averageHeight = (sum of 4 neighbouring Heights)/4
- Sphere Move Simulation
This shader calculates wave pattern based on sphere movement.
height.y += volume in water (oldCenter)
height -= volume in water(newCenter)
- Obj Shading
Load the obj by Threejs obj loader, then shade it by diffuse BRDF.
- Obj Shadow
As triangle test is very expensive in the shader, we use Shadow Map technique instead of raytraced shadow.
This is done by rendering a depth texture a from the point of view of light. Then in the shader, transform vertex into the light view space, determine shadow by the following rule
if(position.z > depth) ---> part of shadow
- Obj Reflection & Refraction
This can be turn on under GUI
draw_obj_reflect. The idea is similar to shadow map, to render a reflection texture from the point of view of reflection point, and use this texture for shading the water.
Now the reflection and refraction positions are not right, to be fixed in the future.
- God Rays
God rays is a Volumetric light scattering effect due to shadows. To implement this effect we take depth information as input and blurs a mask generated from the depth map along radial lines emanating from the light source.
As you can see, as more simulation shader added into the pipeline, the performance evetually drops. But all the fps is above 60, which means our WebGL Water is truly fast and real-time.
Obj mesh interaction: not much influence -bounding sphere, not ray traced
God rays: Drop down FPS by 30 -3 passes, write to texture -6 samples each pass
- Right Mouse Button – rotate
- Left Mouse Button – interact
- Middle Mouse Wheel – zoom
- GUI – change skybox, change object, add wind/rain effect