Projectors and outputs

To your laptop, a projector is just a second screen. prism draws each projector's picture in a window of its own, which you open on that screen and make fullscreen. This page covers opening that window, checking it with Identify, reading the status light, and what changes with a wireless projector.

1Connect the projector

1. Connect the projector to the laptop, with HDMI if you can (USB-C and DisplayPort adapters work the same way).
2. Make it an extended display, not a mirror of the laptop: on Windows press Win + P ▸ Extend; on a Mac, turn off mirroring in Displays settings.
3. In the projector's own menu, switch off auto-keystone, auto-focus and eco / dynamic dimming. Each of these changes the picture by itself, which would move or dim your mapping.
4. Aim it at your scene and focus the lens by hand.

The Projector checklist at the bottom of the Outputs step lists the same four things; tick them as you go.

2Open the projector window

1. On the card, click Open window. A new browser window opens: this is what the projector will show.
2. Drag the window onto the projector's screen. (Or let prism put it there: see Find screens.)

3Fullscreen on the right screen

1. With the window on the projector, click inside it (or press F in it). It fills the projector's screen and hides the mouse pointer.
2. The card changes from Open, not fullscreen (amber) to Live · fullscreen (green).
3. The card's Resolution is now the projector's own: the window's size in real pixels.

4Identify

Identify shows a test pattern on that projector: its name, its resolution, a grid, a crosshair with a circle, colour bars and a grey ramp.

5The status light

The light in the top bar sums up everything in one dot and a few words, the worst thing first. Click it for the details.

6The card's More…

In Simple the card shows only what you need to get going. More… at the bottom shows the rest (Advanced always shows it):

7Wireless projectors

Some projectors take their picture over Wi-Fi, for example through Epson iProjection. To Windows the projector then looks like an extra screen, and every picture is compressed and sent over the network. prism works with this, but each picture arrives late: typically 0.2 to 1.5 seconds, with the odd pause of several seconds.

• prism notices. A window on a screen whose name says wireless (such as Epson's “EPSON IDD”) makes the card say “Wireless display: scans wait for its delay. HDMI is faster and more accurate.” The phone also measures the delay while it frames.
• The scan waits for every picture, so it takes about 2 minutes instead of half a minute. The phone and the laptop both show “Wireless projector detected — ~0.9 s delay. This scan will take about 2 minutes. HDMI is faster and more accurate.”
• If the link stalls for good, the scan stops with a message that says so, and suggests HDMI.

8The picture delay and the beat

The picture delay is how long after the laptop draws a picture this projector shows it. A scan measures it and keeps it with the projector (“≈ 0.9 s (measured by the last scan)”); for a projector that was never scanned you can type it in milliseconds (“set by hand”). Clear the field to forget it.

Why it matters for music: on a slow link, a flash on the beat would land late. So prism draws beat effects on that projector early, by its delay less the tenth of a second a cable already has, and they land on the beat. The ? beside Picture delay tells you by how much. Levels and drum hits follow the sound as it happens, so they can't be drawn early and still arrive late.

Hints and tips

• Use the projector's native resolution in the computer's display settings: the window then draws every projector pixel one to one.
• Name your projectors when there are several; the names appear in Identify and everywhere else.
• Keep the laptop awake. The projector window keeps its screen on, but check the laptop's own sleep settings before a long show.
• Blackout in the top bar (or B in the projector window) darkens every projector at once.
• Stuttering? Press P in the projector window for a small performance display (frame times). Smooth numbers with a stuttering picture point at the display link rather than prism.

When something looks wrong

Mouse and keyboard

Related