ViewshedKernelShaderProgram

GPU kernel shader for earth.worldwind.shape.ViewshedSightline. Renders a fullscreen triangle over an N×N off-screen FBO; each fragment performs an Amanatides–Woo grid traversal from the observer to its own target cell, sampling elevations from an R32F texture and writing RGBA8 visible / occluded / transparent. The result is read back to CPU and projected via earth.worldwind.shape.SurfaceImage.

Requires GLES 3 / WebGL 2 / GL 3.3 core: the kernel uses texelFetch, sized float-format texture sampling, and the out vec4 fragment output. glslVersion is overridden to emit #version 300 es / #version 330 core rather than the legacy 1.20 directive.