According to my proposed timeline, I was supposed to work on quadtree LOD implementation in this week. As I already implemented procedural terrain generator noise functions, I just needed to work on Landscape class to implement the LOD functionality. This would have increased the rendering performance for larger terrains. But as I started into the fourth week, I realized that I might have to make changes in the terrain shaders. This shifted my focus on understanding the shaders, as I am new to GLSL. So finally I decided to implement the Triplanar Texture mapping instead of quadtree.
Problem with Planar texture mapping
Normally, textures are mapped to a surface using UV coordinates which are 2D in nature. So while mapping textures to a particular surface, we don't take height difference between two neighbouring UV coordinates under consideration and just map the textures. This is the gist of Planar texture mapping. So the problem arises is that the neglected hight difference might cause texture to stretch between two points. Unlike simple objects where we can try unwrapping the UV coordinates, in procedurally generated objects it is hard to know the nature of surface and so the corresponding UV unwrapping.
Solution? Triplanar Texture mapping
The Triplanar texture mapping is rendering the same texture three times along the X, Y and Z axis. The fragments that are facing the corresponding directions gets that texture applied to it according to the ratio of the normalized and absolute world space normal. So essentially we are using actual world coordinates instead of UV to apply texture three times in the fragment shader of the material.
Above is a comparison of Planar vs Triplanar texture mapping using the same texture. Notice how textures are stretched in the upper picture while in the lower picture, the original dimensions are somewhat maintained. Although the results are somewhat less desirable due to blending anomalies.
Steps to Triplanar Textures
Here is an another example with a grassy rock texture to the same terrain that we used earlier. Normal texture mapping stretches the whole texture to the surface which gives it an unrealistic look. Here Triplanar texture comes to the rescue.
Problem with Planar texture mapping
Normally, textures are mapped to a surface using UV coordinates which are 2D in nature. So while mapping textures to a particular surface, we don't take height difference between two neighbouring UV coordinates under consideration and just map the textures. This is the gist of Planar texture mapping. So the problem arises is that the neglected hight difference might cause texture to stretch between two points. Unlike simple objects where we can try unwrapping the UV coordinates, in procedurally generated objects it is hard to know the nature of surface and so the corresponding UV unwrapping.
Solution? Triplanar Texture mapping
The Triplanar texture mapping is rendering the same texture three times along the X, Y and Z axis. The fragments that are facing the corresponding directions gets that texture applied to it according to the ratio of the normalized and absolute world space normal. So essentially we are using actual world coordinates instead of UV to apply texture three times in the fragment shader of the material.
Above is a comparison of Planar vs Triplanar texture mapping using the same texture. Notice how textures are stretched in the upper picture while in the lower picture, the original dimensions are somewhat maintained. Although the results are somewhat less desirable due to blending anomalies.
Steps to Triplanar Textures
- Calculate blend factor for each fragment for all the three directions using the world space normal.
- Now sample the texture along the three directions using the world texture coordinates.
- Mix the blend values with the textures to get a final value of textures for that fragment.
- Similar steps can be applied for normal/bump maps.
Here is an another example with a grassy rock texture to the same terrain that we used earlier. Normal texture mapping stretches the whole texture to the surface which gives it an unrealistic look. Here Triplanar texture comes to the rescue.
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| Using Planar Textures with UV mapping |
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| Triplanar Texture mapping |
Problems Faced
I am still having trouble with properly blending the textures from different directions. Some textures like the black and white tiles look really bad as the terrain gets rough. I am still trying to formulate a blending method that will result in better blend factors.
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