Click, hum, flash, prompt. For anyone who grew up with a television tube for a screen, a CRT boot sequence was a small daily ceremony. This demo rebuilds that ceremony on hardware that could never plug into an antenna. Everything you see, from the bulging glass to the scanlines and the burning-in cursor, is math in a shader. Nothing here is a recording.
The Warm-Up Every Eighties Owner Remembers
First came the clunk of the relay and a rising whine from the flyback transformer. Then the bright line snapped across the middle of the glass, and the picture swelled out of that line. Static crackled, the image settled, and the terminal text started typing itself before you had touched anything. If that scene needs no explanation, read my piece on what the Tandy TRS-80 actually was. It was one of the machines that burned this routine into a generation.
Inside the CRT Boot Sequence: What the Shaders Rebuild
The effect is a stack of small physical lies, each one grounded in how the real tubes behaved:
- Barrel distortion. Flat text bows outward near the edges, because electron beams swept a curved face.
- Scanlines. The picture is drawn on an invisible raster, and every dark line between them is visible at this zoom.
- Phosphor glow. Bright characters bleed light into their neighbors, and old frames linger for a fraction of a second.
- Shadow-mask stripes. Red, green and blue phosphor stripes sit under the beam, so sharp edges fracture into color.
- Static, hum flicker and roll. Mains-frequency instability, because analog power supplies were never perfectly steady.
On top of all that, the terminal text is typed one keystroke at a time onto a canvas texture, exactly the way a real BASIC prompt appeared. The CRT shader then distorts that canvas like a lens over a photograph.
Sound Is Half the Memory
Modern browsers refuse to play audio until you interact, so this CRT boot sequence waits for one click. After that, you get the whole soundscape: key clicks, the terminal beep, the 60 Hz hum and the flyback whine that dogs every scan line. Hearing it while typing changes the experience completely. Honestly, the whine is the part that time forgot to let go of.
Why Rebuild It in Shaders at All
Because assets rot and mathematics does not. A video file of a real monitor needs hosting, codecs and bandwidth. This scene needs one HTML file. The same reasoning pushed the story of the Intel 8086 from my own machine to this blog: keep the machinery legible, keep it portable. Every pixel here recomputes at sixty frames per second If you want the physics behind the tube itself, the cathode ray tube article goes deeper than any blog post should.
Try It Yourself
Click once to arm the sound, then watch the boot run. The full power-on animation plays on load, and the prompt keeps a live cursor afterward. Move the mouse slightly and the image breathes with a touch of jitter, the way an aging deflection circuit would.
Where to Go Next
The machine on this screen sits at station one of the interactive computer timeline, which runs the same travel mechanic across five decades of hardware. You can also see how the crystal shader behind all three demos was built at Reverse Engineering igloo.inc — A Deep Dive. Start there if you want the long version of this story.