Slope Blur
Smears a picture or a whole texture set along the slope of a map, for chipped edges, wear, leaks, drips, erosion, and flowing lava.
Every pixel follows a short path that bends with the map: down its slopes, up them, around its contours, or along a flow map. The node then averages what it met on the way, keeps the darkest value, or keeps the brightest. Wire the picture into Image. A second map on Slope steers the smear; with nothing there, the picture steers itself by its own brightness, or a texture set by its own Height. An optional Mask says where the result shows.
For drops that run down glass, each leaving a trail of its own, use Drips instead. Search the node palette for “slope”, “erode”, “smear”, “drip”, or “gravity” to find Slope Blur.
Blur, Min, and Max
Section titled “Blur, Min, and Max”Mode decides what the node does with the values it meets along each path.
- Blur (the default) averages them, so the picture smears along the slope. Use it for running water, streaky wear, flow, and soft erosion.
- Min keeps the darkest value met, so bright areas are eaten from the slope side. Run a bright mask through Min with a noisy Slope map and its edges break up into chips.
- Max keeps the brightest value met, so bright areas grow along the slope. Run a few spots through Max with Gravity and they grow into drips and streaks.
Transparent areas carry no color into the smear: Blur weighs each sample by its alpha, and Min and Max skip fully transparent ones.
Which way the picture moves
Section titled “Which way the picture moves”Direction says which way the content travels.
- Downhill (the default): content runs down the slope, from bright toward dark on the Slope map.
- Uphill: content climbs the slope, from dark toward bright.
- Along Contours: content moves across the slope, counterclockwise on screen around high ground. A noise smeared this way turns into grain, brushed metal, or wood rings.
- Flow Map: the Slope input is a flow map or a normal map, and its red and green say which way and how far each pixel flows. See Flow maps below.
The node never needs a Slope map. With Slope unwired it reads the picture’s own height: a texture set’s Height, or the brightness of a plain picture. That is the “same map into both inputs” trick, done with one wire. A line under Direction always names the source in use:
| Line | When |
|---|---|
| ”Slope from the connected map.” | A map is wired into Slope. |
| ”Slope from the set’s Height.” | Slope is unwired and the set has a Height. |
| ”Slope from the picture’s brightness.” | Slope is unwired on a plain picture, or on a set without a Height. |
| ”Direction from the connected flow map.” | Flow Map, with a map wired. |
| ”Direction from the set’s Normal.” | Flow Map, nothing wired, on a set with a Normal. |
| ”No flow map connected, so the picture moves downhill.” | Flow Map, nothing wired, and no Normal to read. |
The Slope map is read as data: the brightness of its stored values, with no color conversion, the same way Displace reads its map. A Slope map of another size is stretched to the picture. A texture set wired into Slope gives its Height (its Normal under Flow Map); it steers the smear and is never mixed into the result.
Flow maps
Section titled “Flow maps”Under Flow Map, Slope Blur smears the picture along the currents the flow map draws, like a motion blur that bends to follow them. Every pixel stays where it is and gathers color from along its current, so streaks and swirls appear in place.
- Red and green set the direction. More red flows right, less red flows left; more green flows up, less green flows down with Normal Format on OpenGL. DirectX flips green, so set Normal Format to match how your map was saved.
- Distance from gray sets the speed. Mid-gray stays still. A strongly colored pixel flows the full Distance, halfway to gray flows about half as far, and a pixel barely off gray barely moves.
- Blue is ignored. A one-channel map wired under Flow Map says “A flow map needs red and green. This map is gray, so the picture moves downhill.” and the picture does.
Getting a flow map. Paint one: the brush color is the direction and its strength is the speed. Or turn a height map so it follows its contour lines: Noise into Normal Map with Y Direction set to DirectX, then Channel Shuffle with Red taking Green and Green taking Red. The currents then circle the noise’s hills and hollows instead of running into its pits.
A plain normal map of a height field makes color pool rather than flow, because its red and green point downhill: every current runs into the low spots and stops there. That is what Downhill does with the height map wired directly, so use Downhill when pooling is what you want, and a turned or painted flow map when you want currents.
Gravity: drips that run one way
Section titled “Gravity: drips that run one way”Gravity (0 to 1, default 0) and Gravity Angle (default 90, straight down) appear under Downhill and Flow Map. Gravity blends each path from following the slope toward running straight to the angle.
- 0 follows the slope alone.
- 1 runs every pixel straight toward the angle at the full Distance and ignores the slope. This is the clean drip: a few spots, Mode set to Max, Gravity 1, and every spot streaks straight down.
- In between, the flow still runs toward the angle, and the slope’s bumps bend it around them, more the lower Gravity is. From 0.25 up every path runs the full Distance, except where the slope pushes back against the pull, where it slows; below 0.25 the reach eases in from the slope’s own. How much a bump bends a path is measured against the map’s own steepest ground, so it is the same at any Distance and on a gentle map or a sharp one. Around 0.3 to 0.5 with a height map on Slope, drips run the full Distance and wander around rivets, cracks, and lumps instead of running through them.
Gravity Angle uses the screen axis: 0 points right and 90 points down. While Gravity is above 0, an arrow from the center of the Preview points the way it pulls. Drag the arrow’s tip around the center to set Gravity Angle; hold Shift to snap it to steps of 15 degrees, and double-click the tip to set it back to 90. See Canvas handles.
Distance, Fade, and the edges
Section titled “Distance, Fade, and the edges”Distance (default 32 px) is how far the smear reaches, in pixels or in percent of the image’s shorter side with the px / % toggle, so a percent value looks the same at every resolution. 0 returns the input.
The length follows the map: the smear reaches the full Distance wherever the Slope map climbs its whole range within that Distance, and proportionally less on gentler ground. A gentle gradient smears a little, a steep edge smears the full length, and a flat area does not move. To make the smear stronger without changing Distance, steepen the Slope map with Levels. With Gravity at 0.25 or more, every pixel travels the full Distance wherever the slope does not push back against the pull. Very long smears soften slightly across the path, so they never break into separate copies.
- Fade (0 to 1, default 0) tapers the trail. At 0 every step along the path counts equally; at 1 the far end counts for nothing, so leaks and drips end softly instead of in flat bars. Around 0.6 is a good start for drips.
- Slope Softness (default 0 px, hidden under Flow Map) smooths the Slope map before its direction is read. At 0 a fine noise on Slope gives crisp, broken chips. A noisy or hard-edged map can tear a long smear into ragged threads, and a few pixels of softness let those paths run smoothly.
- Edge Mode says what lies past the border. Repeat (the default) wraps both the picture and the Slope map, so a tiling texture stays tiling. Clamp repeats the edge pixel. Open stops a path at the border, so nothing is pulled in from outside.
- Blur Alpha (off by default) keeps the picture’s alpha as it is. Turn it on to smear the alpha with the color, for example to let a cutout run.
Texture sets
Section titled “Texture sets”Wire a texture set into Image and Slope Blur moves every map along the same paths, so the Base Color, Roughness, Normal, and Height stay in register. In Blur mode the Normal is renormalized after averaging, so it stays a direction.
Min and Max pick by Height. On a set with a Height, the step with the lowest (Min) or highest (Max) Height along each path supplies every map’s value, so the color, normal, and roughness follow the eroded or grown surface together instead of each map choosing its own extremes. A set without a Height uses each map’s own extremes, and a line under Mode says “This set has no Height, so Min and Max pick each map’s channels on their own.”
To change several maps at once inside one effect, such as a chip that is bare metal, rough, and dented together, build the mask with Slope Blur and apply it as described in Change several maps under one mask.
Recipes
Section titled “Recipes”- Chipped and worn edges. Curvature’s Convexity (or Bevel’s Height) through Levels into Slope Blur set to Min, with a Voronoi or stone Noise through Levels on Slope. The chips break into the paint from the slope side.
- Leaks and drips. A spot mask into Slope Blur set to Max, Direction Downhill, Gravity 1 at 90, Fade about 0.6, then a Composite set to Lighten over the source. Lower Gravity to about 0.4 with a height map on Slope and the drips wander around its bumps.
- Flowing lava or water. A soft Perlin Noise through Normal Map (Y Direction DirectX) and Channel Shuffle (Red from Green, Green from Red) on Slope with Direction set to Flow Map, over a cracked Voronoi Noise, then a hot Gradient Map. Every map of a set follows the flow the same way.
- Erosion and inflated blobs. Slope Blur set to Min with Direction Uphill and Slope unwired, chained two or three times, wears the peaks down; Blur softens them instead. For inflated blobs, use Max on a thresholded Noise.
- Brushed metal or grain. A fine Noise smeared Along Contours around a Gradient on Slope.
- Rain on a window. Use Drips: every trail keeps its width and runs its own length. Slope Blur set to Max with Gravity 1 and Fade about 0.5 on scattered dots still gives a quick streaked look, with every streak the same length.
Move a picture along a slope without smearing it
Section titled “Move a picture along a slope without smearing it”Slope Blur smears. To move a picture along a slope, a warp, wire the map through Normal Map and into Displace’s map input, with Displace’s Channel set to Red-Green. The normal’s red and green push each pixel along the slope, and Amount X and Amount Y set how far.
- All arithmetic is in float. An 8-bit document is rounded once at the end.
- With GPU Acceleration on, the walk runs on the graphics card for pictures up to 8192 x 8192, in 8-bit and 32-bit documents alike. Larger pictures run on the processor.
- A long cook fills the bar on the node with how far along it is; see Long cooks show their progress.
- Dragging Distance, Fade, or Slope Softness on a large texture set redraws a quick reduced preview while you drag and the full result when you let go.
Parameters
Section titled “Parameters”Pins
Slope Blur
- Blur: averages along the path, smearing the picture along the slope.
- Min: keeps the darkest value met, so bright areas are eaten from the slope side.
- Max: keeps the brightest value met, so bright areas grow along the slope.
Which way the picture moves.
- Downhill: runs down the slope.
- Uphill: climbs the slope.
- Along Contours: moves across the slope, counterclockwise around high ground.
- Flow Map: the Slope input is a normal or flow map. Its red and green set the direction, and how far they are from gray sets how far it flows; gray stays still.
How the flow map was saved. OpenGL has green pointing up, DirectX down
Pulls every path toward Gravity Angle. 0 follows the slope alone. From 0.25 up every path runs the full Distance, and bumps bend it less as Gravity rises; 1 runs straight toward the angle, for clean drips
Which way Gravity pulls, in degrees. 0 = right, 90 = down
How far the smear reaches. It reaches the full Distance where the slope map climbs its full range within that distance, and less on gentler ground; with Gravity, everywhere the slope does not push back. 0 returns the input. Long distances soften slightly across the path
Tapers the trail. At 1 the far end of the path counts for nothing, so leaks and drips end softly
Smooths the slope map before its direction is read, so the smear does not tear
What lies past the border.
- Repeat: wraps the picture and the slope, so a tiling texture stays tiling.
- Clamp: repeats the edge pixel.
- Open: a path stops at the border.
Also smear the alpha. Off keeps the picture's alpha
Mask
How the connected color image is read as a mask
How the mask is sized when it doesn't match the image
Usage Tips
Section titled “Usage Tips”- Leave Slope unwired first: a picture steered by its own brightness, or a set by its own Height, is often all a weathering pass needs.
- Raise Slope Softness a few pixels when a long smear tears into threads; keep it at 0 for crisp chips.
- Keep Edge Mode on Repeat for tiling textures, so the smear wraps across the seam.
- Chain two or three gentle passes rather than one long one for erosion: each pass wears the surface the last one left.