// emulated noperspective
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#if defined(GL_EXT_frag_depth) && !defined(LOG_DEPTH)
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varying float v_WindowZ;
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#endif
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/**
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* Emulates GL_DEPTH_CLAMP, which is not available in WebGL 1 or 2.
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* GL_DEPTH_CLAMP clamps geometry that is outside the near and far planes,
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* capping the shadow volume. More information here:
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* https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_depth_clamp.txt.
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*
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* When GL_EXT_frag_depth is available we emulate GL_DEPTH_CLAMP by ensuring
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* no geometry gets clipped by setting the clip space z value to 0.0 and then
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* sending the unaltered screen space z value (using emulated noperspective
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* interpolation) to the frag shader where it is clamped to [0,1] and then
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* written with gl_FragDepth (see czm_writeDepthClamp). This technique is based on:
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* https://stackoverflow.com/questions/5960757/how-to-emulate-gl-depth-clamp-nv.
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*
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* When GL_EXT_frag_depth is not available, which is the case on some mobile
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* devices, we must attempt to fix this only in the vertex shader.
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* The approach is to clamp the z value to the far plane, which closes the
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* shadow volume but also distorts the geometry, so there can still be artifacts
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* on frustum seams.
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*
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* @name czm_depthClamp
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* @glslFunction
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*
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* @param {vec4} coords The vertex in clip coordinates.
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* @returns {vec4} The modified vertex.
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*
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* @example
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* gl_Position = czm_depthClamp(czm_modelViewProjection * vec4(position, 1.0));
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*
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* @see czm_writeDepthClamp
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*/
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vec4 czm_depthClamp(vec4 coords)
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{
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#ifndef LOG_DEPTH
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#ifdef GL_EXT_frag_depth
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v_WindowZ = (0.5 * (coords.z / coords.w) + 0.5) * coords.w;
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coords.z = 0.0;
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#else
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coords.z = min(coords.z, coords.w);
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#endif
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#endif
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return coords;
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}
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