I have a view where I can display the Earth, and satellites in a 3d view, or 2d view (Mercator). I can send the XYZ data to the shader, and the shader will do the appropriate display for 3d or 2d. In 2d, it does an XYZ to Lat/Lon/Alt conversion in the shader. The problem is as follows: In the 3d view, everything is great:
The 2d view looks good, except for lines that in 3d cross the +/- 180 longitude boundary. The line is of course across the entire earth. What would be better, is if I could break the line into 2 segments (the proposed yellow lines below)
I can't really fix this in the vertex shader, because I only have a single vertex to work with. All options I have come up with are ugly:
- Move LLA conversion to CPU instead of GPU, and split lines there. (Waste of CPU, and doubling of data)
- Multiply all vertices to have "phantom segments" to add segments, and turn segments on/off by changing transparency (up to 4x times the data to the vertex shader, and lots of extra transparent lines to the fragment shader).
Final limitation: This is webgl, so I can't have a geometry shader.
Does anyone have some shader magic or cleverness so that I can keep this on the GPU?