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# Doodle3D Slicer

This document explains how the slice process works.

In this slicer Z is the "up" vector.

Requisites

• 2D Vector math
• 3D Vector math
• 2D Boolean operations (union, difference)
• 2D Path offsetting

### Step 0: Preparation

The first step is to prepare the data for slicing. Most of the model data is mapped into `typed arrays`. This way they can be send to the worker very efficiently (due to the transferable nature of typed arrays).

``````Vertices: Float32Array
Faces: Uint32Array
ObjectIndexes: UInt8Array
OpenObjectIndexes: [...Int]
Settings:
startCode: String
endcode: String
dimensions:
x: Number
y: Number
z: Number
heatedBed: Bool
nozzleDiameter: Number
filamentThickness: Number
temperature: Number
bedTemperature: Number
layerHeight: Number
combing: Bool
thickness:
top: Number
bottom: Number
shell: Number
retraction:
enabled: Bool
amount: Number
speed: Number
minDistance: Number
travel:
speed: Number
support:
enabled: Bool
minArea: Number
distanceY: Number
density: Number
margin: Number
flowRate: Number
speed: Number
innerShell:
flowRate: Number
speed: Number
outerShell:
flowRate: Number
speed: Number
innerInfill:
flowRate: Number
speed: Number
density: Number
outerInfill:
flowRate: Number
speed: Number
brim:
size: Number
flowRate: Number
speed: Number
firstLayer:
flowRate: Number
speed: Number
``````
• Vertices: List of points in 3d
• Faces: Indexes refering to points in the vertices list that make a triangular surface
• ObjectIndexes: Describes of what object each face is part of (important for the generating of 2d shapes)
• OpenObjectIndexes: Determines weather a object is open or closed (important for the generating of 2d shapes)
• Settings: object containing all the settings for slicing. We go in depth in this object when it's needed

### Step 1: Creating lines

In this we take the 3d model and look at each surface to extract all individual lines. Note some lines are part of multiple surfaces. In addition we also add some additional data to each line, like the surfaces it is part of we'll also store the 2d normal.

``````function calculateNormal(vertices, a, b, c) {
a = getVertex(vertices, a);
b = getVertex(vertices, b);
c = getVertex(vertices, c);

const cb = vector3.subtract(c, b);
const ab = vector3.subtract(a, b);
const normal = vector3.normalize(vector3.cross(cb, ab));

return normal;
}
``````

In order to extract all unique lines from the model we'll loop through each face of the model.

### Step 2: Calculate Layers Intersections

This is a fairly straight forward step. We take the lines and calculate on what layers that line will be intersecting. Additinally we calculate the coordinates where the line intersects each layer.

### Step 8: Generate Support

``````let {
brim: { size: brimSize },
nozzleDiameter
} = settings;

nozzleDiameter /= PRECISION;
brimSize /= PRECISION;
const nozzleRadius = nozzleDiameter / 2;

const [firstLayer] = slices;

const brim = firstLayer.parts.reduce((brim, { shape }) => (
endType: shape.closed ? 'etClosedPolygon' : 'etOpenRound'
}))
), new Shape([], true)).simplify('pftNonZero');

firstLayer.brim = new Shape([], true);

for (let offset = 0; offset < brimSize; offset += nozzleDiameter) {
const brimPart = brim.offset(offset, OFFSET_OPTIONS);
firstLayer.brim = firstLayer.brim.join(brimPart);
}
``````