Possible improvements

The first of them, i.e. coastal foam, can be obtained by making an assumption that foam begins at the edge (that is, at the depth equal to 0), and to a certain depth H₁ remains constant, and in the range extincts completely.

Whereas the latter can be achieved by using the following formula:

where:

• H – current height,
• H₀ - height at which foam appears
• H_max - height at which foam dies out.

Another possible extension is to add the interaction between world objects and water. The basic form of interaction will be provided if you use foam as described above. Since it is closely related to the depth at the point of the water area, it will appear wherever the depth is small. As a result it will appear whenever an object falls into the water.

However, the possibilities of interaction between water and the rest of the scene are literally unlimited. By modifying height-map either on CPU or in pixel shader you can easily introduce local disturbance for instance.

Disadvantages of the presented technique

• It increases fill-rate as it is done in post-process and at the same time based on deferred shading. Fortunately, in most cases the water should not occupy more than half of the screen. On the other hand, often there is no need for LOD, since most of the screen pixels will be near the observer.
• Water looks not that good at oblique angles. In order to get rid of this problem, it is possible to apply a different bump mapping technique. The alternative is to move the normal vector towards the observer for distant waves, which will improve their quality, as their back faces will be invisible.
• In the presented approach local lights do not affect the colour of water. You can try to move water rendering before the lighting phase (we can then modify the normal data). This, however, will require modification to the existing rendering chain.

Final results and summary

Image 4 You can achieve many different kinds of water using the presented technique, from tropical warm seas to cold lakes.

The algorithm presented in this paper is a good alternative to the popular techniques used for rendering water effects. By using calculations based on the observation of the phenomenon, rather than on existing mathematical models, I have managed to achieve a realistic effect, which in the case of properly selected parameters’ values makes it possible to achieve results comparable with much more expensive models. It is also a flexible solution - the appearance of water can be controlled through a number of attributes. This makes it suitable for a wide range of effects no matter it be lakes or oceans. You can even have several areas of radically different waters at the very same time.

Besides, as it does not rely on geometry it eliminates the most common flaws of the popular techniques discussed in more detail in the section “Traditional approaches to water rendering” of this article.

A word on implementation

Several textures are used in the code:

• heightMap – height-map used for waves generation as described in the section “Modifying existing geometry”
• backBufferMap – current contents of the back buffer
• positionMap – texture storing scene position vectors
• normalMap – texture storing normal vectors for normal mapping as described in the section “The computation of normal vectors”
• foamMap – texture containing foam – in my case it is a photo of foam converted to greyscale
• reflectionMap – texture containing reflections rendered as described in the section “Reflection and refraction of light”

As water is rendered as a post-process effect, a full-screen quad has to be rendered on the screen with the water shader applied.

Further reading