#ifdef LOG_DEPTH
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varying float v_depthFromNearPlusOne;
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#ifdef POLYGON_OFFSET
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uniform vec2 u_polygonOffset;
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#endif
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#endif
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/**
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* Writes the fragment depth to the logarithmic depth buffer.
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* <p>
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* Use this when the vertex shader does not call {@link czm_vertexlogDepth}, for example, when
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* ray-casting geometry using a full screen quad.
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* </p>
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* @name czm_writeLogDepth
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* @glslFunction
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*
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* @param {float} depth The depth coordinate, where 1.0 is on the near plane and
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* depth increases in eye-space units from there
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*
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* @example
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* czm_writeLogDepth((czm_projection * v_positionEyeCoordinates).w + 1.0);
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*/
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void czm_writeLogDepth(float depth)
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{
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#if defined(GL_EXT_frag_depth) && defined(LOG_DEPTH)
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// Discard the vertex if it's not between the near and far planes.
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// We allow a bit of epsilon on the near plane comparison because a 1.0
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// from the vertex shader (indicating the vertex should be _on_ the near
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// plane) will not necessarily come here as exactly 1.0.
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if (depth <= 0.9999999 || depth > czm_farDepthFromNearPlusOne) {
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discard;
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}
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#ifdef POLYGON_OFFSET
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// Polygon offset: m * factor + r * units
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float factor = u_polygonOffset[0];
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float units = u_polygonOffset[1];
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// If we can't compute derivatives, just leave out the factor I guess?
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#ifdef GL_OES_standard_derivatives
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// m = sqrt(dZdX^2 + dZdY^2);
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float x = dFdx(depth);
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float y = dFdy(depth);
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float m = sqrt(x * x + y * y);
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// Apply the factor before computing the log depth.
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depth += m * factor;
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#endif
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#endif
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gl_FragDepthEXT = log2(depth) * czm_oneOverLog2FarDepthFromNearPlusOne;
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#ifdef POLYGON_OFFSET
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// Apply the units after the log depth.
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gl_FragDepthEXT += czm_epsilon7 * units;
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#endif
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#endif
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}
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/**
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* Writes the fragment depth to the logarithmic depth buffer.
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* <p>
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* Use this when the vertex shader calls {@link czm_vertexlogDepth}.
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* </p>
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*
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* @name czm_writeLogDepth
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* @glslFunction
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*/
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void czm_writeLogDepth() {
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#ifdef LOG_DEPTH
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czm_writeLogDepth(v_depthFromNearPlusOne);
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#endif
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}
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