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Webgl Texture atlas


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#1 peti634   Members   -  Reputation: 101

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Posted 02 August 2014 - 05:31 AM

Hello!

I would like to ask for help concerning the making of the WEBGL Engine. I am stuck at the Texture Atlases. There is a texture, containing 2-2 pictures, and I draw its upper left corner to a vertex (texture coordinates are the following : 0-0.5 0-0.5).

 

This works properly, although when I look the vertex from afar, all of these blur together, and give strange looing colours. I think it is caused, because I use automatically generated Mipmap, and when I look it from afar, the texture unit uses the 1x1 Mipmap texture, where the 4 textures are blurred together to one pixel.

I was suggested the Mipmap’s own generator, with maximum level setting, (GL_TEXTURE_MAX_LEVEL),, although it is not supported by the Webgl. I was also suggested to use the „textureLod” function in the Fragment Shader, but the Webgl only lets me to use it in the vertex shader.

 

The only solution seems to be the Bias, the value that can be given at the 3rd parameter of the Fragment Shader „texture2D” function, but with this, I can only set the offset of the Mipmap LOD, not the actual value.

 

My idea is to use the Depth value (the distance from the camera) to move the Bias (increase it , so it will go more and more negative) so this insures, that it won’t use the last Mipmap level at greater distances, but to always take sample from a higher resolution Mipmap level. The issue with this, that I must calculate the angle of the given vertex to the camera, because the LOD value depends on this.

 

So the Bias=Depth + some combination of the Angle. I would like to ask help calculating this. If someone has any ideas concerning the Webgl Texture Atlases, I would gladly use them. I am looking forward of the answers!

Yours sincerely Peter



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