Reflection rendering into texture

Posted on April 9, 2008. Filed under: Lake water shader, Technical background | Tags: , , , , |

In the chapter describing water mathematics I discussed a method to determine the reflected color for every point of the water surface. One of the most precise solutions for that is creating a virtual view on the other side of the water plane, and rendering the same scene into a texture, which can be used as a reflection map later. This means, that before rendering the final image, a pre-rendering phase should be added. The place of the camera and the view-vector is mirrored onto the water plane during this phase, and every object of the virtual world which can be reflected by the water on the final image is rendered from this virtual view into a texture. Let me show the figure again:

Reflection map

To get the expected result, the place of point B must be calculated. For this, we have to determine how far is the original place of the camera from the water plane, so we have to determine the distance k. If the water is horizontal, this disctance has to be subtracted from the height of the water plane to find the height coordinat, the other coordinates of the points A and B are the same. To avoid artifacts, the underwater objects can be removed from the world before the rendering into texture. When the final image is created, this texture can be used as a reflection-map. The reflective color can be sampled by the help of the vector between the camera and the points of the water surface, and the shape of the waves can be taken into accout as well. Smaller adjustments can be needed to have better results, for instance, smaller modifications of height of the clipping plane or ponit B can improve the reality by producing less artifacts.

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