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Fix bounding volume for tiny ground primitives #4485

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Fix bounding volume for tiny ground primitives #4485

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bb58480
subtract 15
Oct 20, 2016
a5a0018
spec
Oct 21, 2016
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2 changes: 1 addition & 1 deletion Source/Scene/GroundPrimitive.js
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Original file line number Diff line number Diff line change
Expand Up @@ -425,7 +425,7 @@ define([

function getComputeMinimumHeightFunction(primitive) {
return function(granularity, ellipsoid) {
return primitive._minHeight;
return primitive._minHeight - 15;
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15.0 and please add a comment here.

This could also have a significant performance impact for horizon views. How did you come up with 15? I would much rather this depend on the view parameters since 15 meters, for example, could be millions of pixels when zoomed in close.

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What view parameters? This function takes a granularity and an ellipsoid.

There's no specific reason I chose 15. For the code example I pasted above even subtracting 1.0 fixed the problem. From my understanding problem happens when the shadow volume ends exactly at the height the terrain does, so maybe 1.0 would work for all cases? I honestly don't know. @bagnell @tfili what do you think?

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View parameter - where is the camera and what is the FOV. This extrusion should happen in the vertex shader on a frame by frame basis so we don't create huge volumes when zoomed that create a high fillrate load.

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Ah okay. Well that kind of goes beyond my realm of knowledge, so someone else will have to take over here.

};
}

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17 changes: 17 additions & 0 deletions Specs/Scene/GroundPrimitiveSpec.js
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Expand Up @@ -874,6 +874,23 @@ defineSuite([
expect(primitive.getGeometryInstanceAttributes('unknown')).not.toBeDefined();
});

it('has a smaller minimum height to avoid z fighting', function() {
primitive = new GroundPrimitive({
geometryInstances : rectangleInstance
});

spyOn(RectangleGeometry, 'createShadowVolume').and.callThrough();

var frameState = scene.frameState;
primitive.update(frameState);

expect(RectangleGeometry.createShadowVolume).toHaveBeenCalled();
var args = RectangleGeometry.createShadowVolume.calls.allArgs();
var minFunction = args[0][1];
var value = minFunction(rectangle._granularity, rectangle._ellipsoid);
expect(value).toEqual(primitive._minHeight - 15);
});

it('isDestroyed', function() {
primitive = new GroundPrimitive();
expect(primitive.isDestroyed()).toEqual(false);
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