42 lines
1.2 KiB
GLSL
42 lines
1.2 KiB
GLSL
/**
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* Computes the size of a pixel in meters at a distance from the eye.
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* @name czm_metersPerPixel
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* @glslFunction
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*
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* @param {vec3} positionEC The position to get the meters per pixel in eye coordinates.
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*
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* @returns {float} The meters per pixel at positionEC.
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*/
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float czm_metersPerPixel(vec4 positionEC)
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{
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float width = czm_viewport.z;
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float height = czm_viewport.w;
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float pixelWidth;
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float pixelHeight;
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float top = czm_frustumPlanes.x;
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float bottom = czm_frustumPlanes.y;
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float left = czm_frustumPlanes.z;
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float right = czm_frustumPlanes.w;
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if (czm_sceneMode == czm_sceneMode2D || czm_orthographicIn3D == 1.0)
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{
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float frustumWidth = right - left;
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float frustumHeight = top - bottom;
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pixelWidth = frustumWidth / width;
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pixelHeight = frustumHeight / height;
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}
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else
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{
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float distanceToPixel = -positionEC.z;
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float inverseNear = 1.0 / czm_currentFrustum.x;
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float tanTheta = top * inverseNear;
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pixelHeight = 2.0 * distanceToPixel * tanTheta / height;
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tanTheta = right * inverseNear;
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pixelWidth = 2.0 * distanceToPixel * tanTheta / width;
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}
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return max(pixelWidth, pixelHeight);
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}
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