rasterization - students.cs.ubc.cacs-314/vsep2020/... · rasterization © 2020 enrique rosales the...

Rasterization

Computer Graphics

© 2020 Enrique Rosales

Rasterization


The Rasterization stage generates the fragments of each triangle and assigns their interpolated values.

Continuous Discrete

Rasterization


The first step is to define which pixels are inside the triangle.

Rasterization


One option could be to check all pixels to see if they are inside the triangle.

?

Rasterization


One option could be to check all pixels to see if there are inside the triangle.

That would be a bad idea in the case

of having a small triangle inside a huge screen space.

Rasterization


Another option could be to compute a

bounding box first to test only the pixels inside the box.

Rasterization


Another option could be to compute a

bounding box first to test only the pixels inside the box.

Also a bad idea in a case like this.

Rasterization


The solution is an algorithm called “Scan-Line Fill” or “Scan Conversion”

Scan-Line algorithm


We first split the triangle with a horizontal lines.

1

Scan-Line algorithm


We get four edges, that are called “edge trackers.”

𝑒𝑑𝑔𝑒 𝑡𝑟𝑎𝑐𝑘𝑒𝑟𝑠

Scan-Line algorithm


For each edge tracker, we compute its intersection with each row of pixels.

2𝑒𝑑𝑔𝑒 1

Scan-Line algorithm



2

𝑒𝑑𝑔𝑒 2

Scan-Line algorithm



2

𝑒𝑑𝑔𝑒 3

Scan-Line algorithm



2𝑒𝑑𝑔𝑒 4

Scan-Line algorithm


We get a set of pixels ordered by the edge trackers.

2

Scan-Line algorithm


We sort the pixels by scan line (row) and increasing x-coordinate.

3

Scan-Line algorithm


Fill the span between pairs of intersections.

4

Scan-Line algorithm


Final result

Scan-Line algorithm


We can do the same to an entire set of triangles.

Scan-Line algorithm


This is also called “Trapezoid splitting”

Scan-Line algorithm


This is also called “Trapezoid splitting”

https://patents.google.com/patent/US20040257607

Sadhana Gupta et al.

Scan-Line algorithm


However, this is good for large triangles but not so fast for high-density meshes.

https://patents.google.com/patent/US20040257607

Sadhana Gupta et al.

Scan-Line algorithm


However, this is good for large triangles but not so fast for high-density meshes.

https://tinyurl.com/y4gne4teMust see:

This method is not as relevant anymore, its an old school method.

The “edge walking” is still interesting

Modern Solution


?

Modern Solution


Modern GPUs (2020) use edge equations.

Modern Solution


The problem is parallelized by rasterizing a coarse resolution first.

Modern Solution


Then, incrementing the resolution from the sections that survive.

Modern Solution


Until we have the final result.

Computer Graphics


Algorithms evolve depending on hardware, trends, and other factors.

There is no such thing as a dead algorithm.

They can always come back.

Thanks


Composite Transformations

rasterization - students.cs.ubc.cacs-314/vsep2020/... · rasterization © 2020 enrique rosales the...

Documents