Topographic flow guide

Help

Short answers to what goes wrong most often.

The frame says the effect needs WebGL

Topographic flow draws with WebGL, and this browser has it turned off, or lacks the part of it that draws smooth lines. Turn on the browser's graphics acceleration, update it, or try another current browser.

Tapping the picture does nothing

A tap during a run is ignored, so a run is never cut in half. Wait for it to finish, or press Replay, which always starts again at once. A run also only starts from a tap with the main mouse button or a finger.

The lines move but picture B never shows

Check that A → B terrain under Sliders is on. It starts on, and presets and Reset keep it on.

Nothing moves when I tap

With Flow at 0 and A → B terrain off, a run changes nothing. Raise Flow, or turn on A → B terrain.

The map goes the wrong way, or shows picture B

After each run with A → B terrain on, the direction flips: A into B, then B into A. To go back to picture A at once, turn A → B terrain off or press Reset.

The lines look busy or jagged

Fine detail in the picture makes many tiny rings. Raise Smoothing to blur it away, or lower Levels to space the lines out.

My picture looks stretched

The frame takes the shape of picture A, and picture B is stretched to that shape. Crop both pictures to the same shape first. Replacing A changes the frame's shape; replacing B does not.

My picture did not change

A file the browser cannot open as an image is skipped without a message. Try a JPEG, PNG or WebP copy of it. See JPEG, PNG and WebP.

It is slow, or the page struggles with a big photo

The pictures go to the graphics card at their full size, with no resizing, so a very large photo takes more memory. Use a smaller copy on a phone or an older computer. The height is read from a small copy, 256 pixels on its long side, so Smoothing and Levels cost little; the size of the frame does.

Record video did nothing

The line under the buttons says why: some browsers cannot record a canvas, or offer no video format the page can use. Try a current Chrome, Edge or Firefox.

Where do my pictures go?

Nowhere. They are opened in your browser and drawn on your graphics card. Nothing is uploaded. The pictures you add stay on this device, in this browser, so the other lab tools can open them too; × on a picture removes it.

Are there keyboard shortcuts?

The tool has none of its own. Anywhere in the lab, Ctrl K, or Cmd K on a Mac, opens the list of all tools.

On a phone

It works with a finger: tap the picture to start a run. The controls sit in a bar at the bottom of the screen; tap the bar to open them.