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Fix cracking between quantized terrain tiles in 2D. #3486

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merged 3 commits into from
Jan 28, 2016
Merged

Fix cracking between quantized terrain tiles in 2D. #3486

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628f673
Fix cracking between quantized terrain tiles in 2D.
bagnell Jan 28, 2016
cf33df7
Update CHANGEs.md.
bagnell Jan 28, 2016
03c21d9
Merge master to 2d-cracking
pjcozzi Jan 28, 2016
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1 change: 1 addition & 0 deletions CHANGES.md
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@ Change Log
* Added a Sandcastle example to "star burst" overlapping billboards and labels.
* Added `Rectangle.union` and `Rectangle.expand`.
* Added `Math.logBase` function.
* Fixed a cracking between tiles in 2D. [#3486](https://github.com/AnalyticalGraphicsInc/cesium/pull/3486)

### 1.17 - 2016-01-04

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18 changes: 17 additions & 1 deletion Source/Scene/GlobeSurfaceTileProvider.js
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Expand Up @@ -24,6 +24,7 @@ define([
'../Core/PrimitiveType',
'../Core/Rectangle',
'../Core/SphereOutlineGeometry',
'../Core/TerrainQuantization',
'../Core/Visibility',
'../Core/WebMercatorProjection',
'../Renderer/Buffer',
Expand Down Expand Up @@ -68,6 +69,7 @@ define([
PrimitiveType,
Rectangle,
SphereOutlineGeometry,
TerrainQuantization,
Visibility,
WebMercatorProjection,
Buffer,
Expand Down Expand Up @@ -890,6 +892,7 @@ define([
}

var rtc = surfaceTile.center;
var encoding = surfaceTile.pickTerrain.mesh.encoding;

// Not used in 3D.
var tileRectangle = tileRectangleScratch;
Expand Down Expand Up @@ -924,6 +927,20 @@ define([
tileRectangle.w -= rtc.z;
}

if (frameState.mode === SceneMode.SCENE2D && encoding.quantization === TerrainQuantization.BITS12) {
// In 2D, the texture coordinates of the tile are interpolated over the rectangle to get the position in the vertex shader.
// When the texture coordinates are quantized, error is introduced. This can be seen through the 1px wide cracking
// between the quantized tiles in 2D. To compensate for the error, move the expand the rectangle in each direction by
// half the error amount.
var epsilon = (1.0 / (Math.pow(2.0, 12.0) - 1.0)) * 0.5;
var widthEpsilon = (tileRectangle.z - tileRectangle.x) * epsilon;
var heightEpsilon = (tileRectangle.w - tileRectangle.y) * epsilon;
tileRectangle.x -= widthEpsilon;
tileRectangle.y -= heightEpsilon;
tileRectangle.z += widthEpsilon;
tileRectangle.w += heightEpsilon;
}

if (projection instanceof WebMercatorProjection) {
southLatitude = tile.rectangle.south;
northLatitude = tile.rectangle.north;
Expand Down Expand Up @@ -1071,7 +1088,6 @@ define([
uniformMap.waterMask = waterMaskTexture;
Cartesian4.clone(surfaceTile.waterMaskTranslationAndScale, uniformMap.waterMaskTranslationAndScale);

var encoding = surfaceTile.pickTerrain.mesh.encoding;
uniformMap.minMaxHeight.x = encoding.minimumHeight;
uniformMap.minMaxHeight.y = encoding.maximumHeight;
Matrix4.clone(encoding.matrix, uniformMap.scaleAndBias);
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