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How do computers do it?

A 17-minute video by 9rock about computing mechanisms and algorithms and data structures, on the From scratch shelf. It was posted to r/GraphicsProgramming as “Ray tracing video project”. It is pitched at intermediate level.

9rock, Video, 17 min, 2025, on the From scratch shelf

These aren't photographs. They're numbers calculated by a clever mathematical algorithm called ray tracing.

Study notes

Intermediate, Built from scratch. Step 10 of 10 in How a computer works

Helpful first

• Basic programming
• Vectors and coordinates

What it builds

• Model a camera image by firing rays into a scene.
• Compute where rays intersect simple shapes.
• Build up shading from light, reflection and bounce limits.

Useful moments

• 0:54Defining a ray
• 1:15Bouncing rays with the law of reflection
• 2:05Shading a single sphere

Check yourself: What information does each traced ray need to return to colour one pixel?

Notes are based on metadata, Reddit context and selected English caption passages. They are not a review of every claim in the video.